Journal Logo

The Surviving Sepsis Campaign

The Surviving Sepsis Campaign: Research Priorities for Coronavirus Disease 2019 in Critical Illness

Coopersmith, Craig M. MD, MCCM1; Antonelli, Massimo MD2; Bauer, Seth R. PharmD, FCCM3; Deutschman, Clifford S. MS, MD, MCCM4,5; Evans, Laura E. MD, MSc, FCCM6; Ferrer, Ricard MD, PhD7; Hellman, Judith MD8; Jog, Sameer MD9; Kesecioglu, Jozef MD, PhD10; Kissoon, Niranjan MB BS, MCCM11; Martin-Loeches, Ignacio MD, PhD12,13; Nunnally, Mark E. MD, FCCM14; Prescott, Hallie C. MD, MSc15; Rhodes, Andrew MB BS, MD(Res)16; Talmor, Daniel MD, MPH17; Tissieres, Pierre MD, DSc18; De Backer, Daniel MD, PhD19

Author Information
doi: 10.1097/CCM.0000000000004895


Since the first reported cases of coronavirus disease 2019 (COVID-19) in December 2019, millions of people worldwide have been infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus (1). The majority of patients infected are either asymptomatic or mildly symptomatic. However, a minority of infected patients will go on to be hospitalized, and, of these, a significant proportion will be admitted to the ICU. Mortality estimates vary widely in critically ill patients with COVID-19 with recent reports demonstrating improved outcomes during the course of the pandemic (2,3),

Due to the worldwide devastation caused by the COVID-19 pandemic, there has been an exponential increase in knowledge related to the disease. The quality of the available information related to COVID-19 varies wildly. High-quality rigorous clinical trials and scientific discoveries have gone through peer review and have fundamentally changed both bedside management and understanding of the disease. Simultaneously, immeasurable anecdotal information has been promulgated, both within the medical literature and the lay press. Much of this has not been subjected to peer review or has led to adoption of clinical strategies at the bedside in a manner that is unique to this global challenge. In addition, both prevention of and management of COVID-19 have become politicized in many countries in ways not seen with other diseases, contributing to challenges faced by both the lay public and the medical community. Balancing the needs for rapid knowledge advances and dissemination with fidelity to the scientific method has, at times, proved to be challenging during the pandemic where new discoveries are heralded nearly every week, and “gamechanger” therapies may turn out not to be beneficial or even harmful.

Within this context, numerous guidelines have been published related to the management of COVID-19 (4–7). These guidelines reflect the best available evidence toward understanding SARS-CoV-2 infection and the management of COVID-19. At the same time, they indirectly highlight numerous gaps related to current understanding of a disease which is still very new and is responsible for the worst global pandemic in over a century. In light of the numerous challenges that currently exist, the possibilities for research into COVID-19 are nearly limitless. The goal of this document is for the Surviving Sepsis Campaign to narrow these possibilities down to a small group of research priorities that, if addressed, would lead to improved understanding and outcomes for critical illness caused by COVID-19.



Funding for the research priorities was provided solely by Society of Critical Care Medicine (SCCM) and European Society of Intensive Care Medicine (ESICM). No outside funding was received.

Organization of the Committee

ESICM and SCCM appointed members (including one cochair D.D.B., C.M.C., respectively) from each society to the committee which included the cochairs of the Surviving Sepsis Campaign adult (L.E.E., A.R.) and pediatric (N.K., P.T.) guidelines. Committee members were chosen based upon expertise in a wide variety of topics ranging from clinical management to long-term outcomes to basic science. Since all committee members specialize in intensive care, the research priorities focus on critical illness caused by COVID-19. This is not meant to minimize other vital aspects of COVID-19 research such as vaccine development to prevent disease or potential outpatient therapies for mild disease but instead is based upon the expertise of the panel and a prespecified desire to further understand both pathology and therapy in the patients most likely to die of COVID-19. In keeping with a commitment to diversity from both SCCM and ESICM, diversity (broadly defined but including geographic, gender, profession, specialty, socioeconomic) was expressly considered when populating the committee. Notably, the committee had representatives from 10 countries, representing both high- and middle-income countries. Further, the committee had representation from a variety of specialties including intensive care (including pulmonary/critical care, surgical critical care, anesthesiology critical care, and pediatric critical care), emergency medicine, and pharmacy.

Determination of Research Questions and Priorities

Each task force member was asked to submit research questions on any subject related to COVID-19 that they felt was most important, explicitly not restricting this to any particular areas. The expectation was this open-ended approach would yield questions spanning the entire potential gamut of research related to COVID-19 in critically ill patients. Committee members submitted between five and nine questions each. After combining proposed questions that were nearly identical, a total of 58 potential questions was created (Supplemental Table 1, Supplemental Digital Content 1, The goal was to create questions that were as distinct as possible, with the understanding that there may be some overlap between questions.

The committee was next asked to rank their top seven research priorities in order from these 58 questions. Choices were weighted, so that each respondent’s first choice was worth seven points, second choice was worth six points, etc. This allowed for a weighted ranking based upon 1) the number of panel members who rated a question as a top priority and 2) the relative prioritization of each panel member. The number of points for each research priority is shown in Supplemental Table 2 (Supplemental Digital Content 2, There was no a priori decision about how many priorities would be listed. Instead, the final priority list is based upon a cutoff determined by the cochairs related to the number of votes and weighting of the votes for what constituted broad support for a question posed to the committee. The verbiage of each question presented here was simplified compared with the original (compare Supplemental Table 1, Supplemental Digital Content 1, with Table 1) for the ease of readability. Each question was originally written by a single panel member and then reviewed by the entire panel. All but one question used the format that the Surviving Sepsis Research Committee has used in previous publications of 1) What is known, 2) Gaps in knowledge, and 3) Future directions (8–11) The one exception was the question “how can quality research be performed and assessed during a pandemic?” Since this question directly relates to all 12 research priorities—and all research in general during COVID-19—we opted to address this in a broader manner that is not constrained by the format used for all other questions in a separate discussion that follows the remaining questions. In addition, the cochairs decided to limit the scope of the “What Is Known” section to studies that have undergone peer review as of manuscript submission date and not include studies that have been disseminated via press release or preprint servers. The single exception to this was the SOLIDARITY trial, a, 11,266 patient randomized controlled trial of repurposed antiviral drugs which we have included due to its size with the explicit caveat that the trial has not yet undergone peer review (12).

TABLE 1. - Top Ranked Research Questions Developed by the Surviving Sepsis Campaign Research Committee
Should the approach to ventilator management differ from the standard approach in patients with acute hypoxic respiratory failure?
Can the host response be modulated for therapeutic benefit?
What specific cells are directly targeted by SARS-CoV-2 and how do these cells respond?
Can early data be used to predict outcomes of COVID-19 and, by extension, to guide therapies?
What is the role of prone positioning and noninvasive ventilation in nonventilated patients with COVID-19?
Which interventions are best to use for viral load modulation and when should they be given?
Do endothelial cells play a central role in driving and/or potentiating COVID-19 disease?
What is the best approach to anticoagulation in patients with COVID-19?
What are mechanisms of vascular dysfunction and thrombosis in COVID-19 and why are thrombotic manifestations more common in SARS-CoV-2 infection compared with other infections or causes of critical illness?
How can quality research be performed and assessed during a pandemic?
Do the long-term sequelae of severe COVID-19 disease differ from sequelae of sepsis/acute respiratory distress syndrome?
How does SARS-CoV-2 impair immune function?
What are the predictors of ICU admission in COVID-19?
COVID-19 = coronavirus disease 2019, SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.

Conflict of Interest Policy

No industry input into the research priorities was obtained, and no members of the research committee received financial compensation or honoraria for their participation. The process relied on a pre-existing conflict of interest policy and personal disclosure for the Surviving Sepsis Campaign research priorities for sepsis that was updated for this article (8,9).


Questions are presented in order of committee prioritization. When a tie occurred, the question that was rated as a priority by more committee members is listed first compared with a question that was rated as a higher priority by fewer committee members.

1) Should the Approach to Ventilator Management Differ From the Standard Approach in Patients With Acute Hypoxic Respiratory Failure?

What Is Known.

Most patients with COVID-19 admitted to the ICU present with acute respiratory insufficiency. COVID-19–related respiratory insufficiency cases generally fulfill the Berlin description of acute respiratory distress syndrome (ARDS) (13). The Surviving Sepsis Campaign guidelines for managing COVID-19 recommend managing COVID patients with ARDS similarly to classical ARDS patients (6,7). Although patients with respiratory failure from COVID-19 fulfill most or all of the classical criteria of ARDS shortly after ICU admission, their lung mechanics have been observed to, at times, significantly differ from standard ARDS. In many patients, severe hypoxemia is associated with modestly altered lung compliance, a situation that is very uncommon in classical ARDS. The concept that there are different phenotypes in COVID-19–induced respiratory failure that require different ventilation strategies which may be distinct from that in classical ARDS has proven to be controversial. A study performed by Ferrando et al (14) on 742 patients concluded that COVID-19 ARDS patients have features similar to other causes of ARDS, with high compliance with lung-protective ventilation and risk of 28-day mortality increasing with degree of ARDS severity. However, they did not differentiate whether the patients had high or low lung compliance at inclusion. Further, Haudebourg et al (15) did not observe differences in respiratory mechanics between patients with COVID-19–induced ARDS and patients with classical ARDS from other causes of similar severity. Specifically, they described that lung compliance and driving pressure were identical although they also noted that airway closure phenomenon was more frequent in COVID-19 ARDS, potentially reflective of changes in airway inflammation. Additionally, recruitability was slightly higher in COVID-19 ARDS, and no relationship between time from symptom onset to lung compliance was identified. Ziehr et al (16) also reported that lung compliance was markedly altered in their patients with COVID-19 ARDS in a small study in which patients had a high response to prone positioning.

Gaps in Knowledge.

There is not global agreement as to whether or not ventilator management should differ in COVID-19 patients from other patients with hypoxic respiratory failure. Gattinoni et al (17) proposed the “L and H” phenotypes in patients with respiratory failure from COVID-19 based on retrospective data, CT scans, case observation, and communication with colleagues. Type L was proposed to represent the beginning of COVID-19 pneumonia, characterized with low elastance (high compliance), low ventilation to perfusion, low lung weight, and low lung recruitability (attributed to mainly open lung). Furthermore, they proposed that hypoxemia occurs in compliant lungs due to a loss of lung perfusion regulation and hypoxic vasoconstriction. In contrast, Type H was proposed as a phenotype seen at later stages, characterized by high elastance, high right-to-left shunt, high lung weight, and high recruitability, similar to severe classical ARDS criteria. Based upon these proposed phenotypes, they suggested rapid intubation of type L patients with large respiratory drive to avoid excessive intrathoracic negative pressures and self-inflicted lung injury, transforming to Type H (17). They also advised avoiding high positive end-expiratory pressure (PEEP) and recruitment attempts and maintain gentle ventilation to avoid further damage. However, some authors have stated that additional information is needed to understand respiratory failure from COVID-19 more comprehensively and that premature phenotyping might expose these patients to considerable and preventable risk (18). Whether or not the H and L types exist (and if so how common they are), whether there are fundamental differences in respiratory failure in patients with COVID-19, and whether this should direct clinical management remain gaps in current knowledge.

Future Directions.

A fundamental question is whether there are different phenotypes in patients with respiratory failure due to COVID-19 that require different management strategies. If so, research is needed to identify the determinants of which phenotype a patient has, if these occur in different patients or consecutively in the same patient and if the evolution from one phenotype to another can be prevented. A complementary question of profound importance is whether lung-protective ventilation with low tidal volume and high PEEP should be applied in all COVID-19 ARDS patients. Further, it has been demonstrated that large respiratory efforts are associated with relapse of respiratory failure in patients with COVID-19–induced ARDS during weaning from mechanical ventilation (19), but it is unknown whether large respiratory efforts at the early stages also contribute to lung deterioration. Research is also needed to determine if standard measurements used in non-COVID patients with respiratory insufficiency (arterial blood gas, respiratory rate, clinical assessment) are the appropriate metrics to determine when to intubate COVID-19 patients and whether this is altered in patients with excessive inspiratory drive. Further, it remains to be determined how best to identify patients who should be intubated early even though gas exchange may be still be acceptable and conversely how to identify patients in whom intubation may potentially be avoided despite hypoxemia. It is also unclear if prone position should be used more liberally in ARDS associated with COVID-19.

2) Can the Host Response Be Modulated for Therapeutic Benefit?

What is Known.

Patients with COVID-19 can have a dysregulated inflammatory and hemostatic response following infection with SARS-CoV-2. Although patients were initially described as having a “cytokine storm,” subsequent larger studies demonstrated that cytokine levels are either equivalent to or lower than seen in other forms of critical illness (20–23). Corticosteroids have been shown to improve 28-day survival in critically ill patients with COVID-19 (24–28), but it is unclear whether their benefit is due to manipulation of the cytokine response or other effects. The largest of multiple randomized controlled trials to support a benefit of corticosteroids in COVID-19 was the Randomized Evaluation of COVID-19 Therapy (RECOVERY) trial which found lower mortality in 2104 patients randomized to dexamethasone compared with usual care (age-adjusted rate ratio, 0.83; 95% CI, 0.75–0.93) (24). Notably, the mortality benefit was restricted to patients on mechanical ventilation (rate ratio, 0.64; 95% CI, 0.51–0.81) or receiving oxygen without invasive mechanical ventilation (rate ratio, 0.82; 95% CI, 0.72–0.94). A meta-analysis of seven randomized controlled trials of various corticosteroids including dexamethasone, hydrocortisone, and methylprednisolone in 1,703 critically ill patients (over 90% on mechanical ventilation) demonstrated improved short-term survival in patients randomized to receive corticosteroids (odds ratio, 0.66; 95% CI, 0.53–0.82) (28).

Gaps in Knowledge.

The host response to SARS-CoV-2 is heterogeneous. Immune profiling suggests distinct “immunotypes” in patients with COVID-19, each with differing T cell and B cell activation characteristics and clinical trajectories (29). Furthermore, a maladapted immunologic response may occur over time in severely ill patients (30). The best way to target the heterogeneous host response is unknown, and where a patient is on their longitudinal inflammatory response may have profound implications for clinical approaches used at the bedside. A large number of host-modulating agents have been examined in randomized controlled trials, propensity matched studies, smaller observational trials, and case series. An incomplete list of agents designed to alter the host response include SARS-CoV-2 immunoglobulins (specific and nonspecific), mesenchymal stem cells, interferon alpha, interferon beta, interleukin-1 inhibitors, interleukin-6 inhibitors, Bruton’s tyrosine kinase inhibitors, and janus kinase inhibitors. Data on each of these (as well as additional experimental agents) are inconclusive to determine whether they are beneficial toward improving survival—or other patient-centric outcome—in patients with COVID-19. There are many reasons behind these gaps in knowledge, but one example is the difficulty in performing well-done randomized trials in the time of a pandemic (see question 10 below). Several uncertainties remain regarding the use of corticosteroids. In particular, only short-term outcomes (21–30 d survival) were evaluated in RECOVERY and the meta-analysis (28). Previous trials of corticosteroids in ARDS demonstrated a negative impact on long-term outcome (evaluated at 60 and 180 d) despite favorable short-term outcomes (31). Also, identification of the patients who mostly benefit from steroids remains uncertain as the RECOVERY trial suggested that the subgroup of patients on mechanical ventilation benefitted most from steroids, whereas the meta-analysis reported the reverse although the number of nonvented patients in the meta-analysis was small and did not include patients from RECOVERY since this trial did not distinguish between critically ill and noncritically ill patients. Additionally, adverse events should be better reported, in particular, occurrence of secondary infections and neuromuscular weakness. Finally, it is unclear if there is efficacy in extracorporeal therapies such as plasmapheresis and cytokine removal with various membranes as has been suggested in nonrandomized cohorts (32,33).

Future Directions.

Fundamentally, modulating the host response requires an appropriate target and the appropriate patient population. A number of targets have been identified including specific cytokines, mediators that augment or suppress inflammation, endothelial activation, etc. Specific targets are outlined above and in other questions in this article; however, the committee explicitly chose not to prioritize which targets should be approached first, as a comprehensive assessment of which elements of the host response are best candidates for modification is beyond the scope of this question. Although conceptually targeting both viral replication and the host response has appeal, limited studies on combination therapy have been performed, and unexpected side effects need to be understood since modulation of the host response may potentially suppress the immune system, which could promote SARS-CoV-2 growth/replication or secondary bacterial infection. In choosing which patients to study, clinical studies to date have predominantly characterized ICU patients by presence/absence of mechanical ventilation and/or high-flow nasal cannula. More broadly, studies have used a seven-point ordinal scale in which ICU patients make up ordinal 7 (mechanical ventilation or ECMO), ordinal 6 (high-flow nasal cannula), and in rare circumstances ordinal 5 (supplemental oxygen alone). Although these studies have shown clear differences between patient populations responding to the same intervention based upon severity of illness, lumping all ICU patients into a single category almost certainly misses critical differences that could be exploited for therapeutic gain. Although the presence/absence of mechanical ventilation has inherent benefit in clinical trials since it is easily measurable, it is also does not account for individual genetic and epigenetic variability, or how patients with different subphenotypes are likely to respond differently to the identical agent. As such, biomarker or physiomarker enriched trials may lead to a more detailed understanding of which patients would benefit, be harmed, or have no effect from manipulating the host response. Further, specifically distinguishing time of disease from symptom onset, from hospital admission, and from ICU admission may help stratify which patients would benefit greatest from manipulating the host response.

3) What Specific Cells Are Directly Targeted by SARS-CoV-2 and How Do These Cells Respond?

What is Known.

Although the defining characteristic of COVID-19 is infection-induced hypoxemic respiratory failure, dysfunction has also been reported in multiple other organs. Designing appropriate therapeutic responses requires a knowledge of the mechanisms that the virus uses to enter cells, which may subsequently lead to cellular and then organ dysfunction. SARS-CoV-2 has been isolated in a variety of cells and locations in COVID-19 patients (34). Nucleocapsid antigen or viral RNA has been directly identified in respiratory epithelial cells and in bronchoalveolar lavage fluid, bronchoscopic brush biopsies, sputum samples, nasal and pharyngeal swabs, feces, blood and urine (35), and in the cytoplasm of gastric, duodenal, and rectal glandular epithelium of a COVID-19 patient (36) Coronavirus particles were detected on an endomyocardial biopsy in a patient who later died of Gram-negative pneumonia (37). Autopsy results revealed substantial deposition of SARS-CoV-2 in pneumocytes and renal tubular epithelial cells, with lesser amounts in heart, liver, brain, and blood (38,39). Microscopic examination of the kidney specimens revealed clusters of spiked particles in tubular epithelium and podocytes (40).

Primarily based on studies of other coronaviruses, it appears that SARS-CoV-2 enters cells after the viral spike protein attaches to a cell surface receptor (most commonly type 2 angiotensin-converting enzyme [ACE2] [41]), and the spike is cleaved by a protease, typically transmembrane serine protease 2 (TMPRSS2) (42). Use of single-cell RNA sequencing has demonstrated ACE2 and TMPRSS2 coexpression in nasal and bronchial epithelium, especially type II cells (43–46). Low level expression has also been noted in airways, cornea, esophagus, small intestine, colon, liver, gallbladder, heart, kidney, bladder, and testis (47,48). Within the lung and airway, ACE2 is expressed in multiple airway cell types and is most highly expressed in the nasal epithelium. One study using samples obtained via bronchoscopy noted that ACE2 is more highly expressed in the trachea and large airway epithelium than in small airway epithelia (49). TMPRSS2 is more broadly distributed—thus ACE2 is likely a limiting factor in infection (50). Coexpression has also been identified in skin and other “barrier” sites (51). Of note, it has been postulated that the proteolytic function of TMPRSS2 may also be served by cathepsin B or L, which are coexpressed with ACE2 in many different cell types, or by furin, because these proteases are involved in cellular entry of other coronaviruses (49,52,53). In contrast, despite the fact that both SARS-CoV and Middle East respiratory syndrome coronavirus (MERS)-CoV have been shown to infect them, ACE2 is rarely expressed in immune cells (54,55). Cleavage of a protein by a protease, such as TMPRSS2, uncovers a region that then fuses with the membrane of the target cell (42,56) which can result in either direct entry of viral RNA into host cells or the formation of vesicles containing viral replicative material. Although ACE2 also binds other coronaviruses, the affinity of this receptor for SARS-CoV-2 is much higher, explaining its high rate of infectivity (57,58) SARS-CoV-2 can also enter cells via other receptors, which is especially important given the absence of ACE2 on immune cells. CD147 is expressed on T cell catheters and is used for cell entry by the SARS-CoV, HIV-1 and measles viruses (59,60). CD147 interacts with numerous intracellular molecules expressed in immune cells and epithelium and suppresses T cell receptor-dependent activation.

Viral entry into and replication within cells can coopt cellular machinery, preventing cells from performing their normal functions. Alternatively, SARS-CoV-2 might stimulate intracellular pathways to excess, resulting in exhaustion of available cellular energy supplies. Additionally, COVID-19 is associated with damage to and loss of endothelial cells (see question 7 below), accompanied by intra- and extravascular thrombin deposition, occasional microthrombi, and trapped neutrophils (question 9 below). Cardiac abnormalities also include thrombosis, but the most prominently reported abnormality is acute multifocal cardiomyocyte injury. These findings provide potential explanations for COVID-induced myocardial dysfunction (61). Reports of arrhythmias suggest the presence of electrophysiology abnormalities (62) although these changes may reflect effects of SARS-CoV-2 infection on the extracellular milieu.

Acute kidney injury is the most common extrapulmonary manifestation of the disease and is associated with an increased risk of mortality (63,64). Proteinuria and/or hematuria are both common. The presence of SARS-CoV-2 viral particles in tubular cells and in the urine of patients with COVID-19 as well as leak of protein into the urine suggests that the virus causes direct damage to renal cells, but functional data have not been reported (65). Autopsy studies have demonstrated renal abnormalities consistent with ischemia-reperfusion injury. Despite speculation that it is involved in COVID-19 pathology (66), evidence implicating dysfunction of the renin-angiotensin-aldosterone system (RAAS) has not been noted.

Xiao et al (36) reported that 39 of 73 patients with COVID-19 had SARS-CoV-2 RNA in stool. A wide spectrum of GI abnormalities, particularly diarrhea, suggests that SARS-CoV-2 interferes with absorption (67–71), but definitive studies are lacking. Mild-to-moderate elevation of liver enzymes suggests some degree of hepatocellular injury, whereas the presence of congestion, cholestasis, and steatosis suggests either obstruction or defective fatty acid breakdown.

Gaps in Knowledge.

It remains unknown whether other cell types are susceptible to SARS-CoV-2 infection and what other tissues can harbor the virus. It is unclear whether entry of SARS-CoV-2 into cells not expressing ACE2 is dependent on CD147, CD25, or other cell surface proteins. It is unknown whether proteases other than TMPRSS2 contribute to virus uptake. Further, it is unclear if blocking the receptors or impairing the activity of proteases limit viral entry into cells. Although there are multiple drugs that directly affect the mechanisms that facilitate entry of SARS-CoV-2 into cells (72–74), it remains to be determined if these compounds limit SARS-CoV-2 uptake in vivo or are effective in treating COVID-19. Although CD26 has been reported to be a site of entry for MERS-CoV, it remains to be determined if it serves a similar function for SARS-CoV-2 entry into immune cells (75). Finally, little is known about how SARS-CoV-2–induced cellular dysfunction contributes to organ dysfunction and poor outcomes. Proposed mechanisms to explain SARS-CoV-2–induced organ dysfunction include (but are not limited to): 1) direct viral toxicity, 2) abnormalities secondary to ischemia caused by vasculitis/thrombosis/thrombo-inflammation, 3) immune dysregulation, and 4) RAAS dysregulation.

Future Directions.

Given the high expression of viral-uptake genes in the nasal epithelium, intranasal drug administration should be explored. Another line of investigation is to determine how interfering with ACE2 and/or TMPRSS2 (or other receptors or proteases) affect/s normal cellular function. Further exploration of SARS-CoV-2 effects on the pathways used to activate/deactivate immune cell function is worth exploring. The hypothesis that vascular abnormalities underlie pathology in other organ systems should also be examined.

4) Can Early Data Be Used to Predict Outcomes of COVID-19 and, by Extension, to Guide Therapies?

What is Known.

Respiratory symptoms of COVID-19 are extremely heterogeneous, ranging from none (asymptomatic) to minimal symptoms to significant hypoxia with ARDS (76). Although the SARS-CoV-2 virus primarily affects the respiratory system, multiple organ failure can also occur (77). Under the best of circumstances, it is valuable to be able to rapidly identify patients who are likely to require and benefit from hospitalization, ICU admission, and specific therapies. In times of pandemic when resources may be limited, this becomes absolutely vital. This may not only help to determine prognosis and guide the selection of best management strategies for a given individual, but it will also ultimately benefit the largest number of individuals in a resource-limited setting (78).

Clinical data that are useful to the bedside practitioner for prognostication should be simple, objective, easy to collect, and correlated with physiologic variables in acute illness. Multiple risk factors have been identified that are associated with poor prognosis in COVID-19. Although viral load is not a good marker for early categorization (79), patient characteristics such as older age, male gender, higher body mass index, and comorbidities (34,80) have been correlated with worse prognosis. Additionally, racial and ethnic disparities have also been identified (81,82) as being associated with higher risk of poor outcomes in certain countries. Preliminary studies suggest that lymphocyte count may be useful in predicting moderate, severe, and critical illness 1 day after disease onset with an area under the curve (AUC) at 0.81 (79), although this needs to be validated in larger trials. Imaging techniques such as high resolution CT scan (83) or lung ultrasound (84) have also been proposed as tools to evaluate the severity of illness at hospital admission and to predict clinical course and outcome. However, the utility of these modalities may be limited by availability, infection control concerns, operator skillset, and interobserver variability. Genetic factors (85) and ex vivo responses of cells may be informative in evaluating potential disease evolution (86), but these are generally more applicable for research and are less easily measurable at the bedside for broad clinical use.

Gaps in Knowledge.

Beyond obvious respiratory distress and shock, the clinical factors indicating the need for hospitalization and ICU admission vary between hospitals and geographic locations. When a patient is admitted, many variables can be incorporated in a minimal dataset to help identify severe disease earlier and subsequently improve prognosis (87). However, the specific elements to be collected—and their prognostic power—remain to be determined. Multiple biomarkers have been proposed to carry prognostic significance and information about patient trajectory in COVID-19, including (but not limited to) C-reactive protein, serum amyloid A, interleukin-6, lactate dehydrogenase, lymphocyte count, neutrophil-to-lymphocyte ratio, d-dimer, cardiac troponin, renal biomarkers, and platelet count (88). However, the relative importance of each of these has yet to be fully delineated. Further, the majority of these indices have been described in isolation without a concerted effort to compare the respective value of these variables/markers or to construct scores combining the different variables (see question 13 below). Notably, although a COVID-19 Scoring System based on age, presence of chronic heart disease, lymphocyte count, procalcitonin, and d-dimer has been proposed (89), it has not been validated in different settings. Finally, there is significant variability in case fatality across hospitals between geographic regions, according to the prevalence of COVID-19 and need for surge capacity (90–92), whereas the overall mortality for COVID-19 in the ICU has decreased significantly worldwide over time (2). Variability between locations at a point in time and then further longitudinal variability may limit the generalizability of the capacity to predict outcome.

Future Directions.

There is a need for a defined dataset that could potentially include biomarkers, imaging techniques and physiologic variables that phenotype patients with COVID-19. Beyond basic demographic information, identifying clinical factors that can be used to identify patients at risk of disease progression is an important research direction as are identification of biological factors that carry prognostic significance. A “big data” approach using datasets from multiple healthcare systems and multiple countries represents an attractive approach to identify these factors. Conceptually, large datasets could be examined for optimal sensitivity/specificity in a training set using advanced machine learning approaches. This should then be validated using different datasets. Balancing ease of reporting (likely seen with less data elements) with accuracy of prediction (likely seen with more data elements) would be critical in optimizing resulting algorithms. The relative importance—if any—of various imaging techniques requires further study as does prioritization of which imaging should be obtained. Finally, it is important to identify which outcome should be considered. Although the majority of attention to data has focused on survival in hospitalized patients, other patient-centric outcomes should be considered including longer term survival (beyond 28 d), need for sustained organ support (supplemental oxygen, renal replacement therapy), cognitive function, emotional well-being, and long-term physical outcome.

5) What Is the Role of Prone Positioning and Noninvasive Ventilation in Nonventilated Patients With COVID?

What is Known.

Treatment of ARDS in general requires endotracheal intubation and mechanical ventilation. Intubated patients with ARDS can benefit from prone positioning, which improves oxygenation and reduces mortality in non-COVID-19–related moderate-to-severe ARDS (93,94). Ventilated patients with COVID-19 have also shown an excellent response to prone positioning (16).

The COVID-19 pandemic has significantly impacted the capacity of hospitals worldwide, such that patients with moderate-to-severe ARDS are often being treated outside the ICU. The desire to prevent the need for intubation and mechanical ventilation (95,96) has produced significant interest in evaluating the efficacy of prone positioning in nonintubated patients, a strategy that was only rarely tried prior to COVID-19. Several small trials and case series have assessed the feasibility and effectiveness of prone positioning in awake, nonintubated patients with COVID-19 and found the strategy to be promising (97–104). In a prospective, cohort study, Coppo et al (97) proned 56 patients for at least 3 hours with a confirmed diagnosis of COVID-19–related pneumonia and receiving supplemental oxygen or noninvasive continuous positive airway pressure. Pao2/Fio2 ratio increased from 180.5 ± 76 mm Hg in supine position to 285.5 ± 113 mm Hg in prone position (p < 0·0001). These authors concluded that prone positioning was feasible and effective in rapidly ameliorating blood oxygenation in awake patients with COVID-19–related pneumonia requiring oxygen supplementation. In contrast, a multicenter, adjusted cohort study of 199 patients found that patients on high-flow nasal cannula had a 40% chance of being intubated regardless of whether they had awake prone positioning (105).

Gaps in Knowledge.

The efficacy of prone positioning in awake, nonintubated patients with COVID-19–related pneumonia remains unclear. Conceptually, prone positioning in spontaneously breathing patients treated with high-flow oxygen therapy or noninvasive ventilation may prevent the need for intubation, avoiding the risks connected with the ICU stay and ventilator-induced lung injury (106). A number of questions remain regarding both the safety and efficacy of prone ventilation in nonintubated patients. First, does prone positioning actually prevent intubation and reduce the risks associated with invasive mechanical ventilation? There is no way to know based upon the existing literature whether patients who are not intubated using this strategy represent a self-selected group who might otherwise not have progressed to intubation. Next, are there risks associated with delaying a necessary intubation in patients who are selected to prone first? Further, how will treatment failure be recognized on proned patients such that they are rapidly identified and intubated? Also, is there a length of time that spontaneously breathing patients should prone for (either maximal duration or time per session)? Next, it remains to be determined who the best (or at a minimum appropriate) candidates are to receive awake prone positioning.

Future Directions.

Although awake proning for nonintubated patients has rapidly been adopted at multiple centers worldwide, well-conducted trials using a stringent methodologic approach are required to determine whether this should be considered standard of care in a subset of patients with severe COVID-19. Trials should directly examine whether prone ventilation prevents intubation in patients with hypoxemic respiratory insufficiency from COVID-19. In addition to efficacy, trials need to determine whether proning awake patients lead to increased complications from delayed extubation. Finally, if self-proning is effective, trials are required to determine if there is an optimal length of time to prone for, balancing the physiologic benefits of proning with patient comfort.

6) Which Interventions Are Best to Use for Viral Load Modulation and When Should They Be Given?

What Is Known.

Many drugs have been proposed as candidates for potential viral modulation although only a small minority have gone through rigorous clinical trials. Remdesivir is an adenosine nucleotide analog that interferes with the function of the viral RNA-dependent RNA polymerase (107). A multinational National Institutes of Health–sponsored trial of 1,063 patients compared remdesivir with placebo in a double-blind randomized trial (108) with a median time of 9 days from symptom onset to randomization. Remdesivir significantly reduced the time to recovery compared with placebo from 15 days to 11 days in the primary outcome of the trial (recovery rate ratio, 1.32; 95% CI, 1.12–1.55). The benefit of remdesivir was most pronounced in the subgroup of hospitalized patients who required supplemental oxygenation (but not high-flow nasal cannula), and this patient population had a decreased mortality at day 14 in subgroup analysis. In contrast, there was no benefit to remdesivir in either time to recovery or 14-day mortality in patients who required high-flow oxygen, noninvasive ventilation, mechanical ventilation, or ECMO. A concurrent industry-sponsored trial randomized 402 nonintubated patients to receive either 5 days or 10 days of remdesivir (109). No difference in outcomes were noted between treatment lengths. Finally, a multicenter double-blind trial compared remdesivir with placebo in China. A total of 237 patients were enrolled (158 received remdesivir, 79 received placebo). No difference in time to clinical improvement or mortality was identified. However, the study was terminated early because it did not reach its target enrollment of 453 patients, making it difficult to interpret as it was underpowered to reach its primary endpoint (110).

Chloroquine and hydroxychloroquine with or without azithromycin have been studied extensively in COVID-19. Despite early enthusiasm for the drugs (alone or in combination), these drugs have not been shown to be beneficial in multiple randomized trials and large retrospective observational trials (111–113), and they are not recommended for use. Further, safety concerns have been raised with adverse effects of these agents being higher than seen in placebo arms.

Plasma from patients who have recovered from COVID-19 may contain antibodies that could both suppress the virus and modify the host inflammatory response (114). After early usage of convalescent plasma in China to treat hospitalized patients with COVID-19 (115), randomized trials began in multiple countries. In the United States, an expanded access program was developed in parallel with these trials in order to provide broader access to this agent, but without the intent to generate definitive data on safety or efficacy. Ultimately, over 70,000 patients in the United States received this therapy in an unblinded fashion, without a control arm to determine whether or not it was effective. Based upon a retrospective subset analysis from the expanded access program suggesting that high-titer convalescent plasma might be more effective compared with low-titer convalescent plasma in subsets of hospitalized patients, the Food and Drug Administration in the United States issued an Emergency Use Authorization—which is not drug approval but rather facilitates availability and unapproved use during a public health emergency (116).

Lopinavir is used as a retroviral therapy to exert an anti-HIV effect through HIV-1 viral protease inhibition, and ritonavir boosts the effects of lopinavir (117). In the context of coronaviruses, the 3CL protease is the target. The combination of lopinavir and ritonavir has been used for the treatment of MERS (118). A randomized trial of these two agents in 199 patients did not find a benefit in time to improvement or mortality compared with usual care, nor was a difference noted in detectable viral RNA (119). Notably, the treatment was stopped in 13.8% of patients because of adverse events. Additionally, a pharmacokinetic study showed that plasma concentration using typical doses of lopinavir and ritonavir is lower than levels that may be needed to inhibit SARS-Cov-2 replication (120).

Ivermectin is an antiparasitic drug that inhibits importin alpha/beta-1 nuclear transport proteins, which are part of an intracellular transport process that viruses interfere with (121). There is a theoretic rationale for using this agent (which has in vitro activity against multiple viruses) in COVID-19 as it inhibits a pathway that suppresses host-antiviral response. However, although ivermectin inhibits SARS-Co-V-2 in vitro, pharmacokinetic and pharmacodynamic studies suggest that achieving the plasma concentration necessary in patients would require doses 100 times higher than those approved for human use and that predicted plasma and lung tissue concentrations would be lower than the half-maximal inhibitory concentration against the virus (122–125).

Gaps in Knowledge.

The efficacy of remdesivir in patients with COVID-19 on noninvasive ventilation or mechanical ventilation is unclear. If there are benefits to remdesivir, the ideal timing of when to start the drug and how long after symptom onset it might be effective remain to be determined in addition to the optimal treatment length. It is also unclear if the combination of corticosteroids and remdesivir is superior to corticosteroids alone in critically ill patients. It is unknown whether any other antivirals (either those listed above or other experimental agents) improve any patient-centric outcome in COVID-19.

Of note, although this article was under peer review, the results of the World Health Organization-sponsored SOLIDARITY trial on repurposed antiviral drugs for COVID-19 was released in preprint form (12). This study included 11,266 adults in 30 countries. Patients were randomized to remdesivir, hydroxychloroquine, lopinavir, interferon plus lopinavir, interferon alone, or no study drug. None of the interventions impacted overall mortality, initiation of ventilation, or hospital stay. This trial had not yet been subjected to peer review when this article was resubmitted.

Future Directions.

Randomized controlled trials need to be performed on remdesivir specifically examining critically ill patients. Preliminary data need to be generated on other antiviral candidates which, if positive, should lead to randomized controlled trials.

7) Do Endothelial Cells Play a Central Role in Driving and/or Potentiating COVID-19 Disease?

What Is Known.

Observations implicate the endothelium as critical in COVID-19 illness. The ACE2 enzyme, important for SARS-CoV-2 binding and internalization (56), is present on endothelial cells and plays a role in angiotensin signaling balance, with effects on apoptosis, vasoconstriction, and inflammatory signaling (126,127). SARS-CoV-2 has been reported to invade and replicate in capillary-like organoids in vitro (128). Data from patients with COVID-19 demonstrate viral infection of endothelial cells (129), a pauci-immune vasculitis (130), thrombin microvascular clot (129–132), megakaryocytes (132,133), and a characteristic intussusceptive angiogenesis that is unique from other viral pneumonias (131). Von Willebrand factor, factor VIII, and thrombomodulin are products released from endothelium that have been demonstrated to be elevated in patients with severe COVID-19 (134). To determine the impact of SARS-CoV (the virus that caused the SARS outbreak) in complement, a preclinical model examined the role of the virus in mice deficient in C3, the central component of complement (135). Compared with infected wild type mice, C3 knockout mice had less weight loss and less respiratory dysfunction despite equivalent viral loads in the lung, with reduced cytokine and chemokine levels in both the lungs and the blood, suggesting the complement system plays an important role as a mediator of coronavirus disease by regulating a systemic preinflammatory response to SARS-CoV infection. The relevance of these preclinical findings is enhanced by observations of significant complement deposition in the interalveolar septa and cutaneous microvasculature in the lung and skin of two patients with COVID-19 (130).

Gaps in Knowledge.

These observations strongly suggest both direct and indirect viral involvement of the endothelium in COVID-19–related disorders such as ARDS, acute kidney injury, thrombosis, and cardiovascular events. At the same time, these data are all associative (except for preclinical mice data using a related virus) and thus cannot support a firm conclusion that the endothelium plays a crucial role in the pathogenesis of COVID-19. An important gap is in understanding the endothelial role in systemic viral dissemination. The role of complement-mediated vasculitis, described in other coronavirus infections, needs to be better characterized for SARS-CoV-2 beyond case reports. Whether the angiogenesis and thrombosis observed in autopsy findings represents a mechanistic step in the pathobiology of COVID-19 or a response to disease drivers is largely unexplored.

Future Directions.

Future investigations should specifically address whether endothelial abnormalities reflect primary steps in the pathogenesis of COVID-19 or secondary effects driven by other cell types/organ systems. Research should focus on imaging techniques (radiographic imaging, staining, markers), in vivo models (animal models, tests of endothelial function), and in vitro studies using primary human endothelial cells and should address different vascular types in studies using SARS-CoV-2. Ideally, such models would provide mechanistic approaches to therapies and offer a means to assess for risk of severe infection or a worsening trajectory. These approaches should address existing endothelial-targeted therapies, ACE2 viral binding and inactivation, manipulation of the coagulation and immune systems, apoptosis, and endothelial cell infection. Further work should also investigate whether endotheliopathies in COVID-19 predict future cardiovascular disease.

8) What Is the Best Approach to Anticoagulation in Patients With COVID-19?

What Is Known.

A high prevalence of venous and thromboembolic events has been reported in COVID-19 patients. Pulmonary embolism (PE) is the most important but increases in deep vein thrombosis (DVT), myocardial infarction, ischemic stroke, arterial thrombosis, and repeated clotting of continuous renal replacement therapy circuits have been identified (61, 136–142). Notably, the high prevalence of thromboembolic events has occurred despite patients being on prophylactic (often higher doses than used for other ICU patients) or even therapeutic anticoagulation. Some of these thrombotic events represent the initial presenting symptoms for hospital admission and may be central to the clinical presentation of COVID-19 (143,144). These diagnosed and sometimes undiagnosed events contribute to the high mortality of COVID-19 patients admitted to the ICU. Increased levels of procoagulant factors including fibrinogen, and d-dimer are associated with higher mortality in patients with COVID-19 (145). Clinical observations and autopsy findings seem to distinguish COVID-19–associated coagulopathy from thrombotic microangiopathy and disseminated intravascular coagulation (DIC) (145–149).

A retrospective study of 4,389 COVID-19 patients demonstrated that compared with no anticoagulation, therapeutic, and prophylactic anticoagulation were associated with lower in-hospital mortality. There was a trend toward improvement in patients started on therapeutic coagulation within 48 hours of admission (risk ratio, 0.86; 95% CI, 0.73–1.02; p = 0.08). In the entire cohort, 89 patients had major bleeding including 3.0% of patients on therapeutic anticoagulation. Of 26 autopsies, 11 (42%) had thromboembolic disease not clinically suspected (150).

Gaps in Knowledge

Despite the widely seen increase in thromboembolic disease, the optimal method for anticoagulation is not known. Multiple study protocols have been published for existing, on-going studies that should help to clarify this question (151–154). However, it is currently unknown whether there is a benefit to empiric therapeutic anticoagulation without clearly documented thromboembolic disease, and if so, in which patient population. Further, it is unclear whether there is a role for higher dose prophylaxis and, if so, in which patients. It is also unclear if specific anticoagulants are preferable in the setting of COVID-19. This lack of clarity has led to recommendations from professional societies regarding optimal anticoagulation that are not entirely harmonized and emphasize patient specific factors in decision-making until additional data are available (155–159).

Future Directions

Clinical trials are needed to determine how to identify patients who may benefit from therapeutic anticoagulation. Further, trials are needed to determine whether to use regular or augmented doses of prophylactic anticoagulation and if a specific patient population benefits from higher doses of prophylactic anticoagulation. The optimal agent(s) for anticoagulation need to be determined. Studies also need to be performed to determine who should be screened for DVT (all patients vs a subset based upon clinical or laboratory findings) and how often screening should be carried out.

9) What Are Mechanisms of Vascular Dysfunction and Thrombosis in COVID-19 and Why Are Thrombotic Manifestations More Common in SARS-CoV-2 Infection Compared With Other Infections or Causes of Critical Illness?

What Is Known.

Severe COVID-19 causes coagulopathy and vascular complications, including DVT, PE, ischemic strokes, myocardial infarction, peripheral arterial thrombosis, and limb ischemia (138,160–164). Thrombosis of extracorporeal circuits has been reported during renal replacement therapy and ECMO (160,161). These thromboembolic complications occur even in patients receiving prophylactic or therapeutic anticoagulation. Autopsy studies have revealed microvascular fibrin deposition and thrombi in organs, intravascular trapping of neutrophils, pulmonary infarcts, severe endothelial injury with intracellular virus, and microangiopathy, as well as higher levels of angiogenesis and new vessel growth than observed in patients infected with influenza virus (131,165).

Elevated d-dimers have been reported in patients with severe COVID-19 disease, and higher levels of d-dimers early in the course have been shown to predict worse outcomes in preliminary studies although this association has been disputed (137,160,161,166,167). Other early findings include normal to elevated fibrinogen, normal to minimally elevated prothrombin time (PT) and partial thromboplastin time (PTT), and normal platelet counts, although studies suggest that platelets are activated (137,148,161,166). One single-center study of 73 patients on mechanical ventilation due to COVID-19 demonstrated positive lupus circulating anticoagulant in 85% of patients, although this finding was not associated with thrombotic complications (168).

Thrombotic complications of COVID-19 occur in large vessels on the venous and arterial sides as well as in the microcirculation, which is distinct from other infectious causes of coagulopathy. Available data suggest that in the early stages, COVID-19–associated coagulopathy is not DIC (137,161,169). However, studies suggest that over the course of unremitting SARS-CoV-2 infection, the coagulopathy evolves to be consistent with DIC (elevated, PT, PTT, d-dimers, and fibrin degradation products) (137,157). COVID-19 also induces hyperviscosity, with plasma viscosity above 3.5 centipoise associated with thrombotic complications (170). Further, COVID-19 has been demonstrated to induce fibrinolysis shutdown as measured by rotational thromboelastometry in a study of 21 patients (171). Notably, 89% of patients with venous thromboembolism met criteria for fibrinolysis shutdown in this study.

Gaps in Knowledge.

The mechanisms of coagulopathy and vasculopathy in COVID-19 are poorly defined. There are gaps in the understanding of 1) host and microbial triggers of coagulopathy and vasculopathy, 2) the roles of inflammation, and of different cell populations (e.g., endothelial cells, platelets, leukocytes) in driving coagulopathy and vasculopathy, 3) the role of angiogenesis in ARDS and other organ injury and failure, and 4) why the thrombotic complications of COVID-19 are different from other infectious diseases. Although mechanisms remain to be determined, hypoxia-induced vasoconstriction with reduced blood flow, endothelial cell inflammation and dysfunction, and hypercoagulability with high concentrations of von Willebrand Factor and other prothrombotic constituents (Virchow’s Triad) could lead to higher risk of micro- and macrovascular thrombosis in severe COVID-19 patients (40,130,172–175). Additionally, identification of which plasma proteins cause COVID-19–induced hyperviscosity remains to be determined.

Future Directions.

Further preclinical, translational, and clinical studies are needed to better understand the mechanisms of COVID-19–induced coagulopathy and vasculopathy. Specific areas of investigation include understanding the role of different cell populations (leukocytes, endothelial cells, epithelial cells, platelets) and of inflammation in driving the vascular complications of COVID-19 and defining similarities and differences in the mechanisms and course between COVID-19–associated vasculopathy and coagulopathy versus other infectious diseases. Clinical trials to determine whether targeting hyperviscosity via plasma exchange improves outcomes are warranted. Further, additional studies are required to determine the physiologic importance of fibrinolysis shutdown and if this can be targeted clinically.

10) Do the Long-Term Sequelae of Severe and Critical COVID-19 Disease Differ From Sequelae of Sepsis/ARDS?

What Is Known.

Over the past 15 years, multiple studies have demonstrated that both acute respiratory failure and general critical illness are often followed by multifaceted and long-lasting sequelae (176,177). The term “postintensive care syndrome” was established in 2012 to raise awareness of new or worsened physical, cognitive, and emotional symptoms following critical illness (177). Critical illness survivors also have increased risk for recurrent infection, rehospitalization, and death (176). Many ICU survivors cannot return to work or regain functional independence, even 6–12 months after acute illness (178,179). A meta-analysis of 28 studies including 2,820 patients infected with SARS or MERS found high rates of posttraumatic stress disorder (38%), depression (33%), and anxiety (30%) at 6 months post illness, as well as pulmonary dysfunction, reduced exercise tolerance, and reduced health-related quality of life (180).

Due to the recency of the pandemic, the long-term outcomes from severe and critical COVID-19 are unknown. However, survivors are anticipated to experience similar issues (181), creating a large demand for rehabilitative services (182). Early reports from Italy indicate high rates of persistent symptoms at 60 days, particularly fatigue (183). Similarly, a study from the United States found that 40% of patients surviving hospitalization for COVID were unable to resume normal activities within 60 days of discharge (184). There are increasing articles in lay media about COVID-19 survivors with persistent symptoms—coined “long COVID”—and patients have spontaneously formed online support groups (185,186).

Gap in Knowledge.

Because of the newness of the pandemic, relatively limited information exists about long-term outcomes of patients who recover from COVID-19, the expended duration of sequelae, and how these vary by severity of initial COVID-19 disease. It is unclear if long-term sequelae of severe and critical COVID-19 are similar to postintensive care syndrome or if they are distinct (albeit potentially overlapping) entities with unique causes and manifestations. The International Sepsis Forum recently identified key gaps in sepsis survivorship research (187). Gaps include limited information for specific patient populations (e.g., in lower income countries and children), few studies of in-hospital or posthospital interventions to enhance recovery, and limited data on how to identify patients who are likely to benefit from recovery-focused interventions (187).

Future Directions.

Longitudinal cohort studies are needed to define the prevalence of individual sequelae after COVID-19, the average duration of sequelae, and the variation in prevalence across patient subgroups (e.g., subgroups defined by disease severity). Ideally, such studies would be embedded within existing longitudinal cohorts to capture patients’ baseline pre-COVID health status or use proxy-respondent questionnaires or interrogation of available health records to capture this. Second, interventional or comparative effectiveness studies are needed to determine the best practices during and after hospitalization to limit physical and cognitive sequelae. For example, the optimal timing, duration, intensity, and patient selection for mobility interventions remain unclear. Third, studies are needed to improve the implementation of practices already known to improve long-term outcomes (e.g., ABCDEF bundle) but which are more difficult to implement during the pandemic due to high census and infection control precautions. Finally, given the number of patients surviving severe COVID-19 disease, there is an urgent need to test scalable follow-up and recovery programs such as centralized telehealth clinics to screen for and address new cognitive impairments, functional disability, new and worsening symptoms, and chronic comorbidities.

11) How Does SARS-CoV-2 Impair Immune Function?

What Is Known.

Immunologic profiling reveals a significant heterogeneity associated with severity of COVID-19 and temporal changes during the course of the disease (29,188–191). Invariably, SARS-CoV-2 infection results in broad changes in circulating immune cell populations, humoral responses, and cellular functionality. Patients with COVID-19 often have severe persistent lymphopenia despite having an elevated WBC count. This finding is not associated with lymphocyte recruitment to the respiratory tract but may result from a peripheral depletion secondary to systemic inflammation or apoptosis (192). It is also associated with an oligoclonal plasmablast expansion and heterogeneous T cell activation affecting both memory CD4+ and CD8 + T cells (188,193). In a study of 44 patients, Qin et al (20) noted decreases in the total number of CD4+ and CD8+ T cells, B cells and Natural Killer cells at admission. Numbers of both helper and cytotoxic T cell subsets were also decreased, but the T helper/T suppressor ratio was normal as was theinterferon γ response of these cells to phorbol myristate acetate/ionomycin. In contrast, other researchers have found impaired cytokine production in CD8+ T cells (194). Studies have also found that surviving T cells isolated from COVID-19 patients appear functionally exhausted (195,196).

Neutrophilia is also an important hallmark of severe COVID-19. The loss of cell surface Fcγ receptor III CD16 on natural killer and neutrophils phenotypically signals an exaggerated immature neutrophilia (CD10LowCD101CXCR4±) and consequent emergency myelopoiesis and altered neutrophil response (189,197,198). Neutrophil recruitment, entrapment in organs, and neutrophil extracellular traps-osis development may explain vascular thrombosis, vasculitis, and postinfective complications (199–201). Monopenia is also systematically identified in the most severe cases. A decrease of nonclassical CD14LowCD16High, accumulation of human leukocyte antigen (HLA)–DRLow classical monocytes, and consecutive decrease in monocytes HLA – DR isotype expression are associated with acquired immunodepression and associated decrease in monocyte functionality. It has also been reported in a study of 987 patients with life-threatening COVID-19 pneumonia and 1,227 healthy individuals that 10% of patients have neutralizing autoantibodies against type I interferons (202). These neutralizing autoantibodies, like inborn errors of type I interferon production, may tip the balance in favor of the virus in the severe forms of the disease, with insufficient innate and adaptive immune responses. The authors show multiple lines of evidence to suggest that these autoantibodies preceded infection with SARS-CoV-2 and concluded that they accounted for the severity of the disease.

Gaps in Knowledge.

Although the early days of the pandemic have been accompanied by an explosion of knowledge on how the immune system is impacted by SARS-CoV-2 infection, significantly more remains to be discovered. A more comprehensive analysis of cells in both the innate and adaptive immune system in multiple immunologic components remains to be performed. How the immune system is impacted by (and/or helps propagate) the severity of the disease is mostly unknown. Although preliminary studies have longitudinally evaluated the immune system over time, the kinetics of how viral infection impacts the immune system are less well understood, and very little is known about long-term effects after patients are discharged from the hospital. Although the impact of medical comorbidities, age, and gender on the immune system have all been extensively analyzed outside the scope of COVID-19, how each of these interacts with the host immune response during SARS-CoV-2 infection remains to be determined. Whether immunophenotypes can be used for either prognostication or for targeted treatment via precision medicine is unknown. The importance of neutralizing autoantibodies remains to be more definitively determined.

Future Directions.

Variability of infection severity as well as occurrence of postinfective complications, as seen in children with acute myocarditis (203,204), suggests complex immune-pathophysiology involving at a minimum 1) age-specific immunity (e.g., early-age, senescent immunity); 2) immunization status (e.g., against coronavirus species, long-/short-lasting immunization, immunoglobulin specificity, and subclasses); 3) serologic response (e.g., immune complex, complement system); and 4) impact of acquired- or induced-immunosuppression (e.g., pregnancy, systemic diseases, cancer, immunotherapy). To unravel this complex response requires investigations in critically ill patients with appropriate clinical matching to characterize the immune system and leads to potential immunomodulatory therapy. This can be coupled with preclinical studies, autopsy studies, and larger scale biorepository studies to lead to a more comprehensive understanding of the immune response in COVID-19.

12) What Are the Predictors of ICU Admission in COVID-19?

What Is Known.

COVID-19–related disease has placed an enormous strain on ICU resources globally, and in some areas, the demand for ICU services has outstripped the supply. Being able to identify patients requiring ICU care is therefore critical to proper utilization of a scarce resource. There are now numerous reports on the epidemiology and characteristics of COVID-19 patients. Some patient characteristics associated with ICU admission, include male sex, obesity, and chronic kidney disease (205). Among the initial biological variables (as discussed in question 4), lymphocytes and neutrophil-to-lymphocyte ratio may be beneficial (79,206,207), whereas imaging modalities such as chest CT scan and lung ultrasound may also be helpful (84,208). In addition, detection of viral RNA may have prognostic implications since SARS-CoV-2 RNA was detected more frequently, and levels were higher in a recent study of 123 patients admitted to the ICU (209).

Initial attempts have also been made to derive and validate risk prediction scores. An example is the COVID-19–specific score (COVID-GRAM) which used characteristics of COVD-19 patients at time of admission to the hospital in a development cohort of 1,590 patients to predict critical illness (defined as admission to the ICU, mechanical ventilation or death) (210). Factors included in the score were chest radiographic abnormality, age, hemoptysis, dyspnea, unconsciousness, number of comorbidities, cancer history, neutrophil-to-lymphocyte ratio, lactate dehydrogenase, and direct bilirubin. The score performed well in a validation cohort of 710 patients with an AUC of 0.88. Liu et al (211) compared the performance of seven existing severity scores in predicting mortality in 673 COVID-19 patients admitted to the hospital floor. They found the National Early Warning Score had the highest performance with an AUC of 0.88 (211). In addition, a risk score generated from 641 patients with COVID-19 for predicting ICU admission or death (70% training, 30% testing) identified five significant variables predicting ICU admission and seven significant variables predicting death with an AUC of 0.74 for predicting ICU admission and 0.83 for predicting death (212).

Gaps in Knowledge.

It is unclear whether any single variable carries significant prognostic information related to disease progression and ICU admission. Further, the generalizability of all prediction models is uncertain. Not only do they need to be validated in different healthcare systems in different countries, scores may be influenced by rapidly changing protocols for the care of COVID-19 patients.

Future Directions.

As multicenter data bases become available, new severity scores will be developed that are more likely to reflect a broad population. Studies need to determine if a single score can be used universally to predict ICU admission. Further, studies need to determine if prediction scores perform better than clinical assessment, biomarkers or imaging techniques, and if they can be made simple enough for wide usage and accurate enough to have clinical applicability at the bedside. Since there are no a priori reasons to suggest that one approach will be superior to another, we advocate approaching the development of predictive tools using a wide range of approaches including (but not limited to) algorithmic development using multiple machine learning, regularized regression analyses, and logistic regression.


A final research priority was the question “How can quality research be performed and assessed during a pandemic?” This question directly relates to all 12 research priorities above and more globally, to all research being performed in the midst of the current pandemic. To address this question, we start with a quote from the first line of an editorial from Doug Altman (213) published over 25 years ago that has direct relevance to current times—“We need less research, better research, and research done for the right reasons.” Research in COVID-19 has mushroomed in the most challenging of times, when practitioners are faced with a new, highly contagious disease, often in the setting of limited resources with clinical demands outstripping staffing.

Yet, during this pandemic, it is important to conduct rigorous, timely, relevant, ethical research to improve care and outcomes (214). Indeed, the need for research focused on the optimal outcome for the individual patient should be balanced by the need for maximal societal benefit (214). With the large number of critically ill patients, significant mortality rates, and few therapeutic options of proven benefits, it is tempting to relax rigorous research standards and offers therapies of dubious benefits (215). Yet, studies conducted during COVID-19 should be held to the same high ethical, methodologic, and implementation standards as during nonpandemic periods (216,217). Funding priorities should be driven by the broader needs of the community based on the need for resilient health systems which are able to support research (218). Research priorities cannot be a “one size fits all” but rather take into account local factors as to what optimal utility of the proposed study might be. For instance, in high-income countries, research on the modes of ventilation may be prioritized, whereas in low- and middle-income countries, research on optimal delivery of supplemental oxygen may confer greater benefit (219,220). We hereby outline many of the important issues to consider in research conduct during COVID-19:

  • 1) “Optimizing randomized controlled trials in COVID-19 research”—In a rapidly evolving disease, clinical studies should include short-term efficacy evaluation along with long-term efficacy indicators. The randomized controlled trial is firmly entrenched as a key method for evaluation of therapies, whereas observational and nonrandomized trials are generally considered scientifically inferior (221). Randomized trials should be conducted with the same rigor as they are in non-COVID patients. It is important to minimize bias and to collect sufficient data (not just a minimal dataset) in order to ensure absence of imbalance between the treatment arms. For the randomization process, it is important to stratify patients according to key elements associated with outcome determined in a pre hoc manner. In this regard, it is particularly important to stratify patients across different centers, as large differences in outcome may be observed even in centers of the same region (90,91). Cohort studies and pragmatic trials may be alternatives, and newer methodologies such as adaptive design and platform trials offer exciting methods to study patients, even in the time of pandemic (24,25).
  • 2) “Research should be embedded and integrated in critical care when possible”—Embedding research in clinical care such that it becomes standard work, reduces the stress involved in research endeavors when clinicians are already overburdened (222). Implementation science is needed to ensure that the latest discoveries are quickly translated into clinical practice.
  • 3) “Ethical consideration in the conduct of research”—Even in this unprecedented global pandemic, the rights of subjects including voluntary participation, right to be informed, right to privacy and security, and the right to timely treatment should be ensured (223,224). Data safety monitoring committees need to be nimble and quickly adapt to protect subjects such as the re-evaluation of risk and benefit ratios as studies progress (225). In addition, ethics committees should pay attention such that care in the use of experimental drugs, inclusion and exclusion criteria, and informing participants of the risks of the trial are strictly adhered to (226).
  • 4) “Issues of equity, benefits and burdens”—COVID-19 has exposed inequities and disparities in health outcomes for minority groups in multiple countries. These disparities may be exacerbated if clinical trials are not designed with equity considerations in mind. Different racial and ethnic backgrounds may respond differently to medical interventions and are underrepresented in clinical trials (227). In addition, careful consideration should be given to the continuation of nonpandemic research using objective transparent criteria and revisited as the pandemic abates (228). Research should be performed in high- and low-and-middle-income countries. Finally, equity also implies that governments and pharmaceutical industry will make effective therapeutics available for all countries at reasonable prices.
  • 5) “Ensuring accurate communication of research findings”—Failure to adequately communicate research findings in the time of a pandemic has important consequences (229). This is especially important in light of heightened interest in the face of social media campaigns, increased lay press reporting and potential panic, and/or unrest in the general public in the setting of a pandemic (230). Infodemiology is now acknowledged by public health organizations and the World Health Organization as an important emergent field of critical practice during the pandemic. This helps to amplify messages that are beneficial to the public and is based on sound scientific principles while attempting to limit inappropriate content that favors political or commercial interests (231). Notably, communication of research findings has been fundamentally altered during the pandemic, with increasing information coming via press release and preprint services prior to manuscripts undergoing peer review. Although there is an inherent benefit in having results enter the public domain as rapidly as possible, this is balanced by a desire for data to be externally vetted and as comprehensive as possible. Ultimately, the core interest of data dissemination after peer review remains; however, there are circumstances in which care will be altered by a trial result (either showing efficacy or lack of efficacy of a treatment) in which there is utility in rapidly releasing study results prior to peer review.


Because of the severity of the worldwide pandemic, knowledge of COVID-19 is advancing with unprecedented speed, with over 75,000 publications in pubmed at the time of this submission. Considering the rapidity of changes in our understanding of the disease and the mandatory time lag between submission of a paper, peer review, and publication, we freely acknowledge that some of what is contained herein will be out of date by the time of publication or shortly thereafter. Nonetheless, there continue to be significant gaps in understanding of a new disease which has impacted the entire world in a way that is unique in generations. We hope this prioritization will serve as a catalyst for urgently needed research for critically ill patients with COVID-19.


1. COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU). 2020. Available at: Accessed November 25, 2020
2. Armstrong RA, Kane AD, Cook TM: Decreasing mortality rates in ICU during the COVID-19 pandemic. Anaesthesia 2020 Aug 10. [online ahead of print]
3. Auld SC, Caridi-Scheible M, Robichaux C, et al.: Declines in mortality over time for critically ill adults with coronavirus disease 2019. Crit Care Med 2020; 48:e1382–e1384
4. NIH COVID-19 Treatment Guidelines: 2020. Available at: Accessed November 25, 2020
5. World Health Organization: Therapeutics and COVID-19: living guideline. 2020. Available at: Accessed November 25, 2020
6. Alhazzani W, Møller MH, Arabi YM, et al.: Surviving sepsis campaign: Guidelines on the management of critically ill adults with coronavirus disease 2019 (COVID-19). Crit Care Med 2020; 48:e440–e469
7. Alhazzani W, Møller MH, Arabi YM, et al.: Surviving sepsis campaign: Guidelines on the management of critically ill adults with coronavirus disease 2019 (COVID-19). Intensive Care Med 2020; 46:854–887
8. Coopersmith CM, De Backer D, Deutschman CS, et al.: Surviving sepsis campaign: Research priorities for sepsis and septic shock. Intensive Care Med 2018; 44:1400–1426
9. Coopersmith CM, De Backer D, Deutschman CS, et al.: Surviving sepsis campaign: Research priorities for sepsis and septic shock. Crit Care Med 2018; 46:1334–1356
10. Deutschman CS, Hellman J, Ferrer Roca R, et al.; Research Committee of the Surviving Sepsis Campaign: The surviving sepsis campaign: Basic/translational science research priorities. Crit Care Med 2020; 48:1217–1232
11. Deutschman CS, Hellman J, Roca RF, et al.; Research Committee of the Surviving Sepsis Campaign: The surviving sepsis campaign: Basic/translational science research priorities. Intensive Care Med Exp 2020; 8:31
12. Peto R, Abdool Karim Q, Alejandria M, et al.; WHO Solidarity Trial Consortium HP: Repurposed Antiviral Drugs for COVID-19 –Interim WHO SOLIDARITY Trial Results. 2020. Available at: Accessed November 25, 2020
13. Ranieri VM, Rubenfeld GD, Thompson BT, et al.: Acute respiratory distress syndrome: The Berlin definition. JAMA 2012; 307:2526–2533
14. Ferrando C, Suarez-Sipmann F, Mellado-Artigas R, et al.: Clinical features, ventilatory management, and outcome of ARDS caused by COVID-19 are similar to other causes of ARDS. Intensive Care Med 2020; 46:1–12
15. Haudebourg AF, Perier F, Tuffet S, et al.: Respiratory mechanics of COVID-19- versus non-COVID-19-associated acute respiratory distress syndrome. Am J Respir Crit Care Med 2020; 202:287–290
16. Ziehr DR, Alladina J, Petri CR, et al.: Respiratory pathophysiology of mechanically ventilated patients with COVID-19: A cohort study. Am J Respir Crit Care Med 2020; 201:1560–1564
17. Gattinoni L, Coppola S, Cressoni M, et al.: COVID-19 does not lead to a “typical” acute respiratory distress syndrome. Am J Respir Crit Care Med 2020; 201:1299–1300
18. Bos LDJ, Sinha P, Dickson RP: The perils of premature phenotyping in COVID-19: A call for caution. Eur Respir J 2020; 56:2001768
19. Esnault P, Cardinale M, Hraiech S, et al.: High respiratory drive and excessive respiratory efforts predict relapse of respiratory failure in critically ill patients with COVID-19. Am J Respir Crit Care Med 2020; 202:1173–1178
20. Qin C, Zhou L, Hu Z, et al.: Dysregulation of immune response in patients with Coronavirus 2019 (COVID-19) in Wuhan, China. Clin Infect Dis 2020; 71:762–768
21. Sinha P, Matthay MA, Calfee CS: Is a “cytokine storm” relevant to COVID-19? JAMA Intern Med 2020; 180:1152–1154
22. Kox M, Waalders NJB, Kooistra EJ, et al.: Cytokine levels in critically ill patients with COVID-19 and other conditions. JAMA 2020; 324:1565–1567
23. Leisman DE, Ronner L, Pinotti R, et al.: Cytokine elevation in severe and critical COVID-19: A rapid systematic review, meta-analysis, and comparison with other inflammatory syndromes. Lancet Respir Med 2020; 8:1233–1244
24. Horby P, Lim WS, Emberson JR, et al.: Dexamethasone in hospitalized patients with COVID-19 - preliminary report. N Engl J Med 2020
25. Angus DC, Derde L, Al-Beidh F, et al.; Writing Committee for the REMAP-CAP Investigators: Effect of hydrocortisone on mortality and organ support in patients with severe COVID-19: The REMAP-CAP COVID-19 corticosteroid domain randomized clinical trial. JAMA 2020; 324:1317–1329
26. Tomazini BM, Maia IS, Cavalcanti AB, et al.; COALITION COVID-19 Brazil III Investigators: Effect of dexamethasone on days alive and ventilator-free in patients with moderate or severe acute respiratory distress syndrome and COVID-19: The CoDEX randomized clinical trial. JAMA 2020; 324:1307–1316
27. Dequin PF, Heming N, Meziani F, et al.; CAPE COVID Trial Group and the CRICS-TriGGERSep Network: Effect of hydrocortisone on 21-day mortality or respiratory support among critically ill patients with COVID-19: A randomized clinical trial. JAMA 2020; 324:1298–1306
28. Sterne JAC, Murthy S, Diaz JV, et al.: Association between administration of systemic corticosteroids and mortality among critically ill patients with COVID-19: A meta-analysis. JAMA 2020; 324:1330–1341
29. Mathew D, Giles JR, Baxter AE, et al.: Deep immune profiling of COVID-19 patients reveals distinct immunotypes with therapeutic implications. Science 2020; 369:eabc8511
30. Lucas M, Stuart LM, Savill J, et al.: Apoptotic cells and innate immune stimuli combine to regulate macrophage cytokine secretion. J Immunol 2003; 171:2610–2615
31. Steinberg KP, Hudson LD, Goodman RB, et al.; National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network: Efficacy and safety of corticosteroids for persistent acute respiratory distress syndrome. N Engl J Med 2006; 354:1671–1684
32. Keith P, Day M, Perkins L, et al.: A novel treatment approach to the novel coronavirus: An argument for the use of therapeutic plasma exchange for fulminant COVID-19. Crit Care 2020; 24:128
33. Yiğenoğlu TN, Ulas T, Dal MS, et al.: Extracorporeal blood purification treatment options for COVID-19: The role of immunoadsorption. Transfus Apher Sci 2020; 59:102855
34. Wang D, Hu B, Hu C, et al.: Clinical characteristics of 138 hospitalized patients with 2019 novel coronavirus-infected pneumonia in Wuhan, China. JAMA 2020; 323:1061–1069
35. Wang W, Xu Y, Gao R, et al.: Detection of SARS-CoV-2 in different types of clinical specimens. JAMA 2020; 323:1843–1844
36. Xiao F, Tang M, Zheng X, et al.: Evidence for gastrointestinal infection of SARS-CoV-2. Gastroenterology 2020; 158:1831–1833.e3
37. Tavazzi G, Pellegrini C, Maurelli M, et al.: Myocardial localization of coronavirus in COVID-19 cardiogenic shock. Eur J Heart Fail 2020; 22:911–915
38. Remmelink M, De Mendonça R, D’Haene N, et al.: Unspecific post-mortem findings despite multiorgan viral spread in COVID-19 patients. Crit Care 2020; 24:495
39. Puelles VG, Lütgehetmann M, Lindenmeyer MT, et al.: Multiorgan and renal tropism of SARS-CoV-2. N Engl J Med 2020; 383:590–592
40. Su H, Yang M, Wan C, et al.: Renal histopathological analysis of 26 postmortem findings of patients with COVID-19 in China. Kidney Int 2020; 98:219–227
41. Li W, Moore MJ, Vasilieva N, et al.: Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature 2003; 426:450–454
42. Matsuyama S, Nagata N, Shirato K, et al.: Efficient activation of the severe acute respiratory syndrome coronavirus spike protein by the transmembrane protease TMPRSS2. J Virol 2010; 84:12658–12664
43. Bertram S, Heurich A, Lavender H, et al.: Influenza and SARS-coronavirus activating proteases TMPRSS2 and HAT are expressed at multiple sites in human respiratory and gastrointestinal tracts. PLoS One 2012; 7:e35876
44. Zhao Y, Zhao Z, Wang Y, et al.: Single-cell RNA expression profiling of ACE2, the receptor of SARS-CoV-2. Am J Respir Crit Care Med 2020; 202:756–759
45. Zou X, Chen K, Zou J, et al.: Single-cell RNA-seq data analysis on the receptor ACE2 expression reveals the potential risk of different human organs vulnerable to 2019-nCoV infection. Front Med 2020; 14:185–192
46. Qi F, Qian S, Zhang S, et al.: Single cell RNA sequencing of 13 human tissues identify cell types and receptors of human coronaviruses. Biochem Biophys Res Commun 2020; 526:135–140
47. Zhang H, Li HB, Lyu JR, et al.: Specific ACE2 expression in small intestinal enterocytes may cause gastrointestinal symptoms and injury after 2019-nCoV infection. Int J Infect Dis 2020; 96:19–24
48. Hamming I, Timens W, Bulthuis ML, et al.: Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis. J Pathol 2004; 203:631–637
49. Zhang H, Rostami MR, Leopold PL, et al.: Expression of the SARS-CoV-2 ACE2 receptor in the human airway epithelium. Am J Respir Crit Care Med 2020; 202:219–229
50. Sungnak W, Huang N, Bécavin C, et al.; HCA Lung Biological Network: SARS-CoV-2 entry factors are highly expressed in nasal epithelial cells together with innate immune genes. Nat Med 2020; 26:681–687
51. Radzikowska U, Ding M, Tan G, et al.: Distribution of ACE2, CD147, CD26, and other SARS-CoV-2 associated molecules in tissues and immune cells in health and in asthma, COPD, obesity, hypertension, and COVID-19 risk factors. Allergy 2020; 75:2829–2845
52. Millet JK, Whittaker GR: Host cell proteases: Critical determinants of coronavirus tropism and pathogenesis. Virus Res 2015; 202:120–134
53. Simmons G, Gosalia DN, Rennekamp AJ, et al.: Inhibitors of cathepsin L prevent severe acute respiratory syndrome coronavirus entry. Proc Natl Acad Sci U S A 2005; 102:11876–11881
54. Chu H, Zhou J, Wong BH, et al.: Middle east respiratory syndrome coronavirus efficiently infects human primary T lymphocytes and activates the extrinsic and intrinsic apoptosis pathways. J Infect Dis 2016; 213:904–914
55. Ziegler CGK, Allon SJ, Nyquist SK, et al.; HCA Lung Biological Network. Electronic address: [email protected]; HCA Lung Biological Network: SARS-CoV-2 receptor ACE2 is an interferon-stimulated gene in human airway epithelial cells and is detected in specific cell subsets across tissues. Cell 2020; 181:1016–1035.e19
56. Hoffmann M, Kleine-Weber H, Schroeder S, et al.: SARS-CoV-2 cell entry depends on ACE2 and TMPRSS2 and is blocked by a clinically proven protease inhibitor. Cell 2020; 181:271–280.e8
57. Wrapp D, Wang N, Corbett KS, et al.: Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation. Science 2020; 367:1260–1263
58. Wang Q, Ding SL, Li Y, et al.: The allen mouse brain common coordinate framework: A 3D reference atlas. Cell 2020; 181:936–953.e20
59. Muramatsu T: Basigin (CD147), a multifunctional transmembrane glycoprotein with various binding partners. J Biochem 2016; 159:481–490
60. Chen Z, Mi L, Xu J, et al.: Function of HAb18G/CD147 in invasion of host cells by severe acute respiratory syndrome coronavirus. J Infect Dis 2005; 191:755–760
61. Klok FA, Kruip MJHA, van der Meer NJM, et al.: Confirmation of the high cumulative incidence of thrombotic complications in critically ill ICU patients with COVID-19: An updated analysis. Thromb Res 2020; 191:148–150
62. Manolis AS, Manolis AA, Manolis TA, et al.: COVID-19 infection and cardiac arrhythmias. Trends Cardiovasc Med 2020; 30:451–460
63. Cheng Y, Luo R, Wang K, et al.: Kidney disease is associated with in-hospital death of patients with COVID-19. Kidney Int 2020; 97:829–838
64. Yang X, Yu Y, Xu J, et al.: Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: A single-centered, retrospective, observational study. Lancet Respir Med 2020; 8:475–481
65. Martinez-Rojas MA, Vega-Vega O, Bobadilla NA: Is the kidney a target of SARS-CoV-2? Am J Physiol Renal Physiol 2020; 318:F1454–F1462
66. Diamond B: The renin-angiotensin system: An integrated view of lung disease and coagulopathy in COVID-19 and therapeutic implications. J Exp Med 2020; 217:e20201000
67. Garland V, Kumar AB, Borum ML: Gastrointestinal and hepatic manifestations of COVID-19: Evolving recognition and need for increased understanding in vulnerable populations. J Natl Med Assoc 2020
68. Han C, Duan C, Zhang S, et al.: Digestive symptoms in COVID-19 patients with mild disease severity: Clinical presentation, stool viral RNA testing, and outcomes. Am J Gastroenterol 2020; 115:916–923
69. Jin X, Lian JS, Hu JH, et al.: Epidemiological, clinical and virological characteristics of 74 cases of coronavirus-infected disease 2019 (COVID-19) with gastrointestinal symptoms. Gut 2020; 69:1002–1009
70. Parohan M, Yaghoubi S, Seraji A: Liver injury is associated with severe coronavirus disease 2019 (COVID-19) infection: A systematic review and meta-analysis of retrospective studies. Hepatol Res 2020; 50:924–935
71. El Moheb M, Naar L, Christensen MA, et al.: Gastrointestinal complications in critically ill patients with and without COVID-19. JAMA 2020; 324:1899–1901
72. Hoffmann M, Schroeder S, Kleine-Weber H, et al.: Nafamostat mesylate blocks activation of SARS-CoV-2: New treatment option for COVID-19. Antimicrob Agents Chemother 2020; 64:e00754–20
73. Doi K, Ikeda M, Hayase N, et al.; COVID-UTH Study Group: Nafamostat mesylate treatment in combination with favipiravir for patients critically ill with COVID-19: A case series. Crit Care 2020; 24:392
74. Tanaka Y, Sato Y, Sasaki T: Suppression of coronavirus replication by cyclophilin inhibitors. Viruses 2013; 5:1250–1260
75. van Doremalen N, Miazgowicz KL, Milne-Price S, et al.: Host species restriction of middle east respiratory syndrome coronavirus through its receptor, dipeptidyl peptidase 4. J Virol 2014; 88:9220–9232
76. Wu C, Chen X, Cai Y, et al.: Risk factors associated with acute respiratory distress syndrome and death in patients with coronavirus disease 2019 pneumonia in Wuhan, China. JAMA Intern Med 2020; 180:934–943
77. Yuki K, Fujiogi M, Koutsogiannaki S: COVID-19 pathophysiology: A review. Clin Immunol 2020; 215:108427
78. Fan E, Beitler JR, Brochard L, et al.: COVID-19-associated acute respiratory distress syndrome: Is a different approach to management warranted? Lancet Respir Med 2020; 8:816–821
79. Tan L, Kang X, Ji X, et al.: Validation of predictors of disease severity and outcomes in COVID-19 patients: A descriptive and retrospective study. Med (N Y) 2020; 1:128–138.e3
80. Grasselli G, Greco M, Zanella A, et al.: Risk factors associated with mortality among patients with COVID-19 in intensive care units in Lombardy, Italy. JAMA Intern Med 2020; 180:1345–1355
81. Wadhera RK, Wadhera P, Gaba P, et al.: Variation in COVID-19 hospitalizations and deaths across New York city boroughs. JAMA 2020; 323:2192–2195
82. Yehia BR, Winegar A, Fogel R, et al.: Association of race with mortality among patients hospitalized with coronavirus disease 2019 (COVID-19) at 92 US hospitals. JAMA Netw Open 2020; 3:e2018039
83. Lu X, Gong W, Peng Z, et al.: High resolution CT imaging dynamic follow-up study of novel coronavirus pneumonia. Front Med (Lausanne) 2020; 7:168
84. Lichter Y, Topilsky Y, Taieb P, et al.: Lung ultrasound predicts clinical course and outcomes in COVID-19 patients. Intensive Care Med 2020; 46:1–11
85. Ellinghaus D, Degenhardt F, Bujanda L, et al.: Genomewide association study of severe COVID-19 with respiratory failure. N Engl J Med 2020; 383:1522–1534
86. Laing AG, Lorenc A, Del Molino Del Barrio I, et al.: Author correction: A dynamic COVID-19 immune signature includes associations with poor prognosis. Nat Med 2020; 26:1951
87. WHO Working Group on the Clinical Characterisation and Management of COVID-19 infection: A minimal common outcome measure set for COVID-19 clinical research. Lancet Infect Dis 2020; 20:e192–e197
88. Kermali M, Khalsa RK, Pillai K, et al.: The role of biomarkers in diagnosis of COVID-19 - a systematic review. Life Sci 2020; 254:117788
89. Shang Y, Liu T, Wei Y, et al.: Scoring systems for predicting mortality for severe patients with COVID-19. EClinicalMedicine 2020; 24:100426
90. Immovilli P, Morelli N, Antonucci E, et al.: COVID-19 mortality and ICU admission: The Italian experience. Crit Care 2020; 24:228
91. Gupta S, Hayek SS, Wang W, et al.: Factors associated with death in critically ill patients with coronavirus disease 2019 in the US. JAMA Intern Med 2020; 180:1–12
92. Auld SC, Caridi-Scheible M, Blum JM, et al.; Emory COVID-19 Quality and Clinical Research Collaborative: ICU and ventilator mortality among critically ill adults with coronavirus disease 2019. Crit Care Med 2020; 48:e799–e804
93. Guérin C, Reignier J, Richard JC, et al.; PROSEVA Study Group: Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013; 368:2159–2168
94. Munshi L, Del Sorbo L, Adhikari NKJ, et al.: Prone position for acute respiratory distress syndrome. A systematic review and meta-analysis. Ann Am Thorac Soc 2017; 14:S280–S288
95. Fagiuoli S, Lorini FL, Remuzzi G; Covid-19 Bergamo Hospital Crisis Unit: Adaptations and lessons in the Province of Bergamo. N Engl J Med 2020; 382:e71
96. Grasselli G, Zangrillo A, Zanella A, et al.; COVID-19 Lombardy ICU Network: Baseline characteristics and outcomes of 1591 patients infected with SARS-CoV-2 admitted to ICUs of the Lombardy Region, Italy. JAMA 2020; 323:1574–1581
97. Coppo A, Bellani G, Winterton D, et al.: Feasibility and physiological effects of prone positioning in non-intubated patients with acute respiratory failure due to COVID-19 (PRON-COVID): A prospective cohort study. Lancet Respir Med 2020; 8:765–774
98. Elharrar X, Trigui Y, Dols AM, et al.: Use of prone positioning in nonintubated patients with COVID-19 and hypoxemic acute respiratory failure. JAMA 2020; 323:2336–2338
99. Sartini C, Tresoldi M, Scarpellini P, et al.: Respiratory parameters in patients with COVID-19 after using noninvasive ventilation in the prone position outside the intensive care unit. JAMA 2020; 323:2338–2340
100. Xu Q, Wang T, Qin X, et al.: Early awake prone position combined with high-flow nasal oxygen therapy in severe COVID-19: A case series. Crit Care 2020; 24:250
101. Taboada M, González M, Álvarez A, et al.: Effectiveness of prone positioning in nonintubated intensive care unit patients with moderate to severe acute respiratory distress syndrome by coronavirus disease 2019. Anesth Analg 2021; 132:25–30
102. Paul V, Patel S, Royse M, et al.: Proning in non-intubated (PINI) in times of COVID-19: Case series and a review. J Intensive Care Med 2020; 35:818–824
103. Ng Z, Tay WC, Ho CHB: Awake prone positioning for non-intubated oxygen dependent COVID-19 pneumonia patients. Eur Respir J 2020; 56:2001198
104. Thompson AE, Ranard BL, Wei Y, et al.: Prone positioning in awake, nonintubated patients with COVID-19 hypoxemic respiratory failure. JAMA Intern Med 2020; 180:1537–1539
105. Ferrando C, Mellado-Artigas R, Gea A, et al.; COVID-19 Spanish ICU Network: Awake prone positioning does not reduce the risk of intubation in COVID-19 treated with high-flow nasal oxygen therapy: A multicenter, adjusted cohort study. Crit Care 2020; 24:597
106. Ripoll-Gallardo A, Grillenzoni L, Bollon J, et al.: Prone positioning in non-intubated patients with COVID-19 outside of the intensive care unit: More evidence needed. Disaster Med Public Health Prep 2020; 14:1–3
107. Tchesnokov EP, Feng JY, Porter DP, et al.: Mechanism of inhibition of Ebola virus RNA-dependent RNA polymerase by remdesivir. Viruses 2019; 11;326
108. Beigel JH, Tomashek KM, Dodd LE, et al.: Remdesivir for the treatment of COVID-19 - preliminary report. N Engl J Med 2020
109. Goldman JD, Lye DCB, Hui DS, et al.: Remdesivir for 5 or 10 days in patients with severe COVID-19. N Engl J Med 2020
110. Wang Y, Zhang D, Du G, et al.: Remdesivir in adults with severe COVID-19: A randomised, double-blind, placebo-controlled, multicentre trial. Lancet 2020; 395:1569–1578
111. Cavalcanti AB, Zampieri FG, Rosa RG, et al.: Hydroxychloroquine with or without azithromycin in mild-to-moderate COVID-19. N Engl J Med 2020
112. Geleris J, Sun Y, Platt J, et al.: Observational study of hydroxychloroquine in hospitalized patients with COVID-19. N Engl J Med 2020; 382:2411–2418
113. Rosenberg ES, Dufort EM, Udo T, et al.: Association of treatment with hydroxychloroquine or azithromycin with in-hospital mortality in patients with COVID-19 in New York State. JAMA 2020; 323:2493–2502
114. Wang X, Guo X, Xin Q, et al.: Neutralizing antibodies responses to SARS-CoV-2 in COVID-19 inpatients and convalescent patients. Clin Infect Dis 2020: ciaa721
115. Li L, Zhang W, Hu Y, et al.: Effect of convalescent plasma therapy on time to clinical improvement in patients with severe and life-threatening COVID-19: A randomized clinical trial. JAMA 2020; 324:460–470
116. U.S. Food and Drug Administration: Emergency Use Authorization of Medical Products and Related Authorities: Guidance for Industry and Other Stakeholders. Available at: Accessed November 25, 2020
117. Croxtall JD, Perry CM: Lopinavir/ritonavir: A review of its use in the management of HIV-1 infection. Drugs 2010; 70:1885–1915
118. Baden LR, Rubin EJ: COVID-19 - the search for effective therapy. N Engl J Med 2020; 382:1851–1852
119. Cao B, Wang Y, Wen D, et al.: A trial of lopinavir-ritonavir in adults hospitalized with severe COVID-19. N Engl J Med 2020; 382:1787–1799
120. Schoergenhofer C, Jilma B, Stimpfl T, et al.: Pharmacokinetics of lopinavir and ritonavir in patients hospitalized with coronavirus disease 2019 (COVID-19). Ann Intern Med 2020; 173:670–672
121. Yang SNY, Atkinson SC, Wang C, et al.: The broad spectrum antiviral ivermectin targets the host nuclear transport importin α/β1 heterodimer. Antiviral Res 2020; 177:104760
122. Caly L, Druce JD, Catton MG, et al.: The FDA-approved drug ivermectin inhibits the replication of SARS-CoV-2 in vitro. Antiviral Res 2020; 178:104787
123. Chaccour C, Hammann F, Ramón-García S, et al.: Ivermectin and COVID-19: Keeping rigor in times of urgency. Am J Trop Med Hyg 2020; 102:1156–1157
124. Guzzo CA, Furtek CI, Porras AG, et al.: Safety, tolerability, and pharmacokinetics of escalating high doses of ivermectin in healthy adult subjects. J Clin Pharmacol 2002; 42:1122–1133
125. Arshad U, Pertinez H, Box H, et al.: Prioritization of anti-SARS-Cov-2 drug repurposing opportunities based on plasma and target site concentrations derived from their established human pharmacokinetics. Clin Pharmacol Ther 2020; 108:775–790
126. Zhang H, Zhang X, Hou Z, et al.: RhACE2 - playing an important role in inhibiting apoptosis induced by Ang II in HUVECs. Medicine (Baltimore) 2019; 98:e15799
127. Zhu L, Carretero OA, Xu J, et al.: Activation of angiotensin II type 2 receptor suppresses TNF-α-induced ICAM-1 via NF-кB: Possible role of ACE2. Am J Physiol Heart Circ Physiol 2015; 309:H827–H834
128. Monteil V, Kwon H, Prado P, et al.: Inhibition of SARS-CoV-2 infections in engineered human tissues using clinical-grade soluble human ACE2. Cell 2020; 181:905–913.e7
129. Varga Z, Flammer AJ, Steiger P, et al.: Endothelial cell infection and endotheliitis in COVID-19. Lancet 2020; 395:1417–1418
130. Magro C, Mulvey JJ, Berlin D, et al.: Complement associated microvascular injury and thrombosis in the pathogenesis of severe COVID-19 infection: A report of five cases. Transl Res 2020; 220:1–13
131. Ackermann M, Verleden SE, Kuehnel M, et al.: Pulmonary vascular endothelialitis, thrombosis, and angiogenesis in COVID-19. N Engl J Med 2020; 383:120–128
132. Carsana L, Sonzogni A, Nasr A, et al.: Pulmonary post-mortem findings in a series of COVID-19 cases from northern Italy: A two-centre descriptive study. Lancet Infect Dis 2020; 20:1135–1140
133. Rapkiewicz AV, Mai X, Carsons SE, et al.: Megakaryocytes and platelet-fibrin thrombi characterize multi-organ thrombosis at autopsy in COVID-19: A case series. EClinicalMedicine 2020; 24:100434
134. Goshua G, Pine AB, Meizlish ML, et al.: Endotheliopathy in COVID-19-associated coagulopathy: Evidence from a single-centre, cross-sectional study. Lancet Haematol 2020; 7:e575–e582
135. Gralinski LE, Sheahan TP, Morrison TE, et al.: Complement activation contributes to severe acute respiratory syndrome coronavirus pathogenesis. mBio 2018; 9:e01753–18
136. Cui S, Chen S, Li X, et al.: Prevalence of venous thromboembolism in patients with severe novel coronavirus pneumonia. J Thromb Haemost 2020; 18:1421–1424
    137. Zhou F, Yu T, Du R, et al.: Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: A retrospective cohort study. Lancet 2020; 395:1054–1062
    138. Lodigiani C, Iapichino G, Carenzo L, et al.; Humanitas COVID-19 Task Force: Venous and arterial thromboembolic complications in COVID-19 patients admitted to an academic hospital in Milan, Italy. Thromb Res 2020; 191:9–14
    139. Richardson S, Hirsch JS, Narasimhan M, et al.; the Northwell COVID-19 Research Consortium: Presenting characteristics, comorbidities, and outcomes among 5700 patients hospitalized with COVID-19 in the New York city area. JAMA 2020; 323:2052–2059
      140. Connors JM, Levy JH: COVID-19 and its implications for thrombosis and anticoagulation. Blood 2020; 135:2033–2040
        141. Llitjos JF, Leclerc M, Chochois C, et al.: High incidence of venous thromboembolic events in anticoagulated severe COVID-19 patients. J Thromb Haemost 2020; 18:1743–1746
          142. Oxley TJ, Mocco J, Majidi S, et al.: Large-vessel stroke as a presenting feature of COVID-19 in the young. N Engl J Med 2020; 382:e60
            143. Miesbach W, Makris M: COVID-19: Coagulopathy, risk of thrombosis, and the rationale for anticoagulation. Clin Appl Thromb Hemost 2020; 26:1076029620938149
            144. Wang T, Chen R, Liu C, et al.: Attention should be paid to venous thromboembolism prophylaxis in the management of COVID-19. Lancet Haematol 2020; 7:e362–e363
            145. Zhang L, Yan X, Fan Q, et al.: D-dimer levels on admission to predict in-hospital mortality in patients with COVID-19. J Thromb Haemost 2020; 18:1324–1329
            146. Yin S, Huang M, Li D, et al.: Difference of coagulation features between severe pneumonia induced by SARS-CoV2 and non-SARS-CoV2. J Thromb Thrombolysis 2020: 1–4
            147. Zhang Y, Xiao M, Zhang S, et al.: Coagulopathy and antiphospholipid antibodies in patients with COVID-19. N Engl J Med 2020; 382:e38
            148. Panigada M, Bottino N, Tagliabue P, et al.: Hypercoagulability of COVID-19 patients in intensive care unit: A report of thromboelastography findings and other parameters of hemostasis. J Thromb Haemost 2020; 18:1738–1742
            149. Jain R, Young M, Dogra S, et al.: COVID-19 related neuroimaging findings: A signal of thromboembolic complications and a strong prognostic marker of poor patient outcome. J Neurol Sci 2020; 414:116923
            150. Nadkarni GN, Lala A, Bagiella E, et al.: Anticoagulation, bleeding, mortality, and pathology in hospitalized patients with COVID-19. J Am Coll Cardiol 2020; 76:1815–1826
            151. Barco S, Bingisser R, Colucci G, et al.: Enoxaparin for primary thromboprophylaxis in ambulatory patients with coronavirus disease-2019 (the OVID study): A structured summary of a study protocol for a randomized controlled trial. Trials 2020; 21:770
            152. Kharma N, Roehrig S, Shible AA, et al.: Anticoagulation in critically ill patients on mechanical ventilation suffering from COVID-19 disease, the ANTI-CO trial: A structured summary of a study protocol for a randomised controlled trial. Trials 2020; 21:769
            153. Houston BL, Lawler PR, Goligher EC, et al.: Anti-thrombotic therapy to ameliorate complications of COVID-19 (ATTACC): Study design and methodology for an international, adaptive Bayesian randomized controlled trial. Clin Trials 2020; 17:491–500
            154. Busani S, Tosi M, Mighali P, et al.: Multi-centre, three arm, randomized controlled trial on the use of methylprednisolone and unfractionated heparin in critically ill ventilated patients with pneumonia from SARS-CoV-2 infection: A structured summary of a study protocol for a randomised controlled trial. Trials 2020; 21:724
            155. Thachil J, Tang N, Gando S, et al.: ISTH interim guidance on recognition and management of coagulopathy in COVID-19. J Thromb Haemost 2020; 18:1023–1026
            156. Becker RC: Covid-19 treatment update: Follow the scientific evidence. J Thromb Thrombolysis 2020; 50:43–53
            157. Tang N, Bai H, Chen X, et al.: Anticoagulant treatment is associated with decreased mortality in severe coronavirus disease 2019 patients with coagulopathy. J Thromb Haemost 2020; 18:1094–1099
            158. Bikdeli B, Madhavan MV, Jimenez D, et al.; Global COVID-19 Thrombosis Collaborative Group, Endorsed by the ISTH, NATF, ESVM, and the IUA, Supported by the ESC Working Group on Pulmonary Circulation and Right Ventricular Function: COVID-19 and thrombotic or thromboembolic disease: Implications for prevention, antithrombotic therapy, and follow-up: JACC state-of-the-art review. J Am Coll Cardiol 2020; 75:2950–2973
            159. Dogra S, Jain R, Cao M, et al.: Hemorrhagic stroke and anticoagulation in COVID-19. J Stroke Cerebrovasc Dis 2020; 29:104984
            160. Iba T, Levy JH, Levi M, et al.: Coagulopathy of coronavirus disease 2019. Crit Care Med 2020; 48:1358–1364
            161. Helms J, Tacquard C, Severac F, et al.; CRICS TRIGGERSEP Group (Clinical Research in Intensive Care and Sepsis Trial Group for Global Evaluation and Research in Sepsis): High risk of thrombosis in patients with severe SARS-CoV-2 infection: A multicenter prospective cohort study. Intensive Care Med 2020; 46:1089–1098
            162. Middeldorp S, Coppens M, van Haaps TF, et al.: Incidence of venous thromboembolism in hospitalized patients with COVID-19. J Thromb Haemost 2020; 18:1995–2002
            163. Klok FA, Kruip MJHA, van der Meer NJM, et al.: Incidence of thrombotic complications in critically ill ICU patients with COVID-19. Thromb Res 2020; 191:145–147
            164. Kashi M, Jacquin A, Dakhil B, et al.: Severe arterial thrombosis associated with Covid-19 infection. Thromb Res 2020; 192:75–77
            165. Buja LM, Wolf DA, Zhao B, et al.: The emerging spectrum of cardiopulmonary pathology of the coronavirus disease 2019 (COVID-19): Report of 3 autopsies from Houston, Texas, and review of autopsy findings from other United States cities. Cardiovasc Pathol 2020; 48:107233
            166. Ranucci M, Ballotta A, Di Dedda U, et al.: The procoagulant pattern of patients with COVID-19 acute respiratory distress syndrome. J Thromb Haemost 2020; 18:1747–1751
            167. Gris JC, Loubet P, Roger C, et al.: The association between D-dimers in COVID-19 patients and mortality remains beset of uncertainties. J Thromb Haemost 2020; 18:2068–2070
            168. Siguret V, Voicu S, Neuwirth M, et al.: Are antiphospholipid antibodies associated with thrombotic complications in critically ill COVID-19 patients? Thromb Res 2020; 195:74–76
            169. Li Y, Zhao K, Wei H, et al.: Dynamic relationship between D-dimer and COVID-19 severity. Br J Haematol 2020; 190:e24–e27
            170. Maier CL, Truong AD, Auld SC, et al.: COVID-19-associated hyperviscosity: A link between inflammation and thrombophilia? Lancet 2020; 395:1758–1759
            171. Creel-Bulos C, Auld SC, Caridi-Scheible M, et al.: Fibrinolysis shutdown and thrombosis in a COVID-19 ICU. Shock 2020
            172. Joly BS, Siguret V, Veyradier A: Understanding pathophysiology of hemostasis disorders in critically ill patients with COVID-19. Intensive Care Med 2020; 46:1603–1606
            173. Han H, Yang L, Liu R, et al.: Prominent changes in blood coagulation of patients with SARS-CoV-2 infection. Clin Chem Lab Med 2020; 58:1116–1120
            174. Campbell CM, Kahwash R: Will complement inhibition be the new target in treating COVID-19-related systemic thrombosis? Circulation 2020; 141:1739–1741
            175. Lippi G, Plebani M, Henry BM: Thrombocytopenia is associated with severe coronavirus disease 2019 (COVID-19) infections: A meta-analysis. Clin Chim Acta 2020; 506:145–148
            176. Prescott HC, Angus DC: Enhancing recovery from sepsis: A review. JAMA 2018; 319:62–75
            177. Needham DM, Davidson J, Cohen H, et al.: Improving long-term outcomes after discharge from intensive care unit: Report from a stakeholders’ conference. Crit Care Med 2012; 40:502–509
            178. McPeake J, Mikkelsen ME, Quasim T, et al.: Return to employment after critical illness and its association with psychosocial outcomes. A systematic review and meta-analysis. Ann Am Thorac Soc 2019; 16:1304–1311
            179. Yende S, Austin S, Rhodes A, et al.: Long-term quality of life among survivors of severe sepsis: Analyses of two international trials. Crit Care Med 2016; 44:1461–1467
            180. Ahmed H, Patel K, Greenwood DC, et al.: Long-term clinical outcomes in survivors of severe acute respiratory syndrome and middle east respiratory syndrome coronavirus outbreaks after hospitalisation or ICU admission: A systematic review and meta-analysis. J Rehabil Med 2020; 52:jrm00063
            181. Hosey MM, Needham DM: Survivorship after COVID-19 ICU stay. Nat Rev Dis Primers 2020; 6:60
            182. Thornton J: COVID-19: The challenge of patient rehabilitation after intensive care. BMJ 2020; 369:m1787
            183. Carfi A, Bernabei R, Landi F: Persistent symptoms in patients after acute COVID-19. JAMA 2020; 324:603–605
            184. Chopra V, Flanders SA, O’Malley M, et al.: Sixty-day outcomes among patients hospitalized with COVID-19. Ann Intern Med 2020
            185. Smith-Spark L, Shelly J, Borghese L: Brain Fog, Fatigue, Breathlessness. Rehab Centers Set Up Across Europe to Treat Long-Term Effects of Coronavirus: CNN, 2020. Available at: Accessed November 25, 2020
            186. Long COVID 2020: Available at:
            187. Prescott HC, Iwashyna TJ, Blackwood B, et al.: Understanding and enhancing sepsis survivorship. Priorities for research and practice. Am J Respir Crit Care Med 2019; 200:972–981
            188. Chen Z, John Wherry E: T cell responses in patients with COVID-19. Nat Rev Immunol 2020; 20:529–536
            189. Silvin A, Chapuis N, Dunsmore G, et al.: Elevated calprotectin and abnormal myeloid cell subsets discriminate severe from mild COVID-19. Cell 2020; 182:1401–1418.e18
            190. McGonagle D, Sharif K, O’Regan A, et al.: The role of cytokines including interleukin-6 in COVID-19 induced pneumonia and macrophage activation syndrome-like disease. Autoimmun Rev 2020; 19:102537
            191. Lucas C, Wong P, Klein J, et al.; Yale IMPACT Team: Longitudinal analyses reveal immunological misfiring in severe COVID-19. Nature 2020; 584:463–469
            192. Liao M, Liu Y, Yuan J, et al.: Single-cell landscape of bronchoalveolar immune cells in patients with COVID-19. Nat Med 2020; 26:842–844
            193. Kuri-Cervantes L, Pampena MB, Meng W, et al.: Comprehensive mapping of immune perturbations associated with severe COVID-19. Sci Immunol 2020; 5;eabd7114
            194. Cossarizza A, Gibellini L, De Biasi S, et al.: Handling and processing of blood specimens from patients with COVID-19 for safe studies on cell phenotype and cytokine storm. Cytometry A 2020; 97:668–673
            195. Diao B, Wang C, Tan Y, et al.: Reduction and functional exhaustion of T cells in patients with coronavirus disease 2019 (COVID-19). Front Immunol 2020; 11:827
            196. Allegra A, Di Gioacchino M, Tonacci A, et al.: Immunopathology of SARS-CoV-2 infection: Immune cells and mediators, prognostic factors, and immune-therapeutic implications. Int J Mol Sci 2020; 21:4782
            197. Schulte-Schrepping J, Reusch N, Paclik D, et al.; Deutsche COVID-19 OMICS Initiative (DeCOI): Severe COVID-19 is marked by a dysregulated myeloid cell compartment. Cell 2020; 182:1419–1440.e23
            198. Drifte G, Dunn-Siegrist I, Tissières P, et al.: Innate immune functions of immature neutrophils in patients with sepsis and severe systemic inflammatory response syndrome. Crit Care Med 2013; 41:820–832
            199. Zuo Y, Yalavarthi S, Shi H, et al.: Neutrophil extracellular traps in COVID-19. JCI Insight 2020; 5:e138999
            200. Barnes BJ, Adrover JM, Baxter-Stoltzfus A, et al.: Targeting potential drivers of COVID-19: Neutrophil extracellular traps. J Exp Med 2020; 217:e20200652
            201. Tissières P, Teboul JL: SARS-CoV-2 post-infective myocarditis: The tip of COVID-19 immune complications? Ann Intensive Care 2020; 10:98
            202. Bastard P, Rosen LB, Zhang Q, et al.: Autoantibodies against type I IFNs in patients with life-threatening COVID-19. Science 2020; 370:eabd4585
            203. Lee PY, Day-Lewis M, Henderson LA, et al.: Distinct clinical and immunological features of SARS-CoV-2-induced multisystem inflammatory syndrome in children. J Clin Invest 2020; 130:5942–5950
            204. Belhadjer Z, Auriau J, Méot M, et al.: Addition of corticosteroids to immunoglobulins is associated with recovery of cardiac function in multi-inflammatory syndrome in children. Circulation 2020; 142:2282–2284
            205. Suleyman G, Fadel RA, Malette KM, et al.: Clinical characteristics and morbidity associated with coronavirus disease 2019 in a series of patients in metropolitan detroit. JAMA Netw Open 2020; 3:e2012270
            206. Liu J, Zhang S, Wu Z, et al.: Clinical outcomes of COVID-19 in Wuhan, China: A large cohort study. Ann Intensive Care 2020; 10:99
            207. Wang W, Zhao Z, Liu X, et al.: Clinical features and potential risk factors for discerning the critical cases and predicting the outcome of patients with COVID-19. J Clin Lab Anal 2020; 34:e23547
            208. Borghesi A, Maroldi R: COVID-19 outbreak in Italy: Experimental chest X-ray scoring system for quantifying and monitoring disease progression. Radiol Med 2020; 125:509–513
            209. Prebensen C, Hre PLM, Jonassen C, et al.: SARS-CoV-2 RNA in plasma is associated with ICU admission and mortality in patients hospitalized with COVID-19. Clin Infect Dis 2020
            210. Liang W, Liang H, Ou L, et al.; China Medical Treatment Expert Group for COVID-19: Development and validation of a clinical risk score to predict the occurrence of critical illness in hospitalized patients with COVID-19. JAMA Intern Med 2020; 180:1081–1089
            211. Liu FY, Sun XL, Zhang Y, et al.: Evaluation of the risk prediction tools for patients with coronavirus disease 2019 in Wuhan, China: A single-centered, retrospective, observational study. Crit Care Med 2020; 48:e1004–e1011
            212. Zhao Z, Chen A, Hou W, et al.: Prediction model and risk scores of ICU admission and mortality in COVID-19. PLoS One 2020; 15:e0236618
            213. Altman DG: The scandal of poor medical research. BMJ 1994; 308:283–284
            214. Cook D, Burns K, Finfer S, et al.: Clinical research ethics for critically ill patients: A pandemic proposal. Crit Care Med 2010; 38:e138–e142
            215. Sattui SE, Liew JW, Graef ER, et al.: Swinging the pendulum: Lessons learned from public discourse concerning hydroxychloroquine and COVID-19. Expert Rev Clin Immunol 2020; 16:659–666
            216. Citerio G, Bakker J, Brochard L, et al.: Critical care journals during the COVID-19 pandemic: Challenges and responsibilities. Intensive Care Med 2020; 46:1521–1523
            217. Kaplan LJ, Bleck TP, Buchman TG, et al.: Pandemic-related submissions: The challenge of discerning signal amidst noise. Crit Care Med 2020; 48:1099–1102
            218. Ezequiel G, Jafet A, Hugo A, et al.: The COVID-19 pandemic: A call to action for health systems in Latin America to strengthen quality of care. Int J Qual Health Care 2020: mzaa062
            219. Camporota L, Vasques F, Sanderson B, et al.: Identification of pathophysiological patterns for triage and respiratory support in COVID-19. Lancet Respir Med 2020; 8:752–754
            220. Baker T, Schell CO, Petersen DB, et al.: Essential care of critical illness must not be forgotten in the COVID-19 pandemic. Lancet 2020; 395:1253–1254
            221. Retsas S: Clinical trials and the COVID-19 pandemic. Hell J Nucl Med 2020; 23:4–5
            222. Fitzsimons J: Quality & safety in the time of coronavirus-design better, learn faster. Int J Qual Health Care 2020
            223. Zhang T, He Y, Xu W, et al.: Clinical trials for the treatment of coronavirus disease 2019 (COVID-19): A rapid response to urgent need. Sci China Life Sci 2020; 63:774–776
            224. Wendler D, Rid A: In defense of a social value requirement for clinical research. Bioethics 2017; 31:77–86
            225. Barnbaum DR: Data safety monitoring during COVID-19: Keep on keeping on. Ethics Hum Res 2020; 42:43–44
            226. Zhang H, Shao F, Gu J, et al.: Ethics committee reviews of applications for research studies at 1 hospital in China during the 2019 novel Coronavirus epidemic. JAMA 2020; 323:1844–1846
            227. Loree JM, Anand S, Dasari A, et al.: Disparity of race reporting and representation in clinical trials leading to cancer drug approvals from 2008 to 2018. JAMA Oncol 2019; 5:e191870
            228. Cook DJ, Kho ME, Duan EH, et al.: Principles guiding nonpandemic critical care research during a pandemic. Crit Care Med 2020; 48:1403–1410
            229. Saitz R, Schwitzer G: Communicating science in the time of a pandemic. JAMA 2020; 324:443–444
            230. Addis A, Genazzani A, Trotta MP, et al.: Promoting better clinical trials and drug information as public health interventions for the COVID-19 emergency in Italy. Ann Intern Med 2020; 173:654–655
            231. Eysenbach G: How to fight an infodemic: The four pillars of infodemic management. J Med Internet Res 2020; 22:e21820

            coronavirus disease 2019; critical illness; intensive care unit; priorities; research; Surviving Sepsis Campaign

            Supplemental Digital Content

            Copyright © 2021 by the Society of Critical Care Medicine and Wolters Kluwer Health, Inc. All Rights Reserved.