Performance of Aerosol Boxes for Endotracheal Intubation during the COVID-19 Pandemic with Systematic Review : Journal of Global Infectious Diseases

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Original Article

Performance of Aerosol Boxes for Endotracheal Intubation during the COVID-19 Pandemic with Systematic Review

Christopher, R. Ajay; Lohanathan, Aparna; Hazra, Darpanarayan; Pal, Rathijit; Vegiraju, Vaishnavi; Abhilash, Kundavaram Paul Prabhakar

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Journal of Global Infectious Diseases 15(1):p 6-12, Jan–Mar 2023. | DOI: 10.4103/jgid.jgid_165_22
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The COVID-19 pandemic left the frontline health-care workers (HCWs) with the herculean task of keeping up with the ever-changing treatment protocols, meeting the supply-demand shortage of resources, all the while facing the risk of exposure to the virus.[1,2] Out of the several aerosol-generating procedures, endotracheal intubation is consistently associated with transmission of the virus across the various studies reviewed, with studies showing an absolute risk increase of between 10% (cohort studies) and 15% (case–control studies) for transmission of severe acute respiratory syndrome coronavirus (SARS-CoV)-1-associated infection to health-care personnel performing intubation.[3,4] Aerosolized particles 5 mm-20 mm spread infection through deposition on the respiratory epithelium and can potentially travel the length of the respiratory tract. It is also possible that these microscopic particles may stay in the air for a prolonged time and be carried further by air currents. A systematic literature review and meta-analysis that evaluated transmission of SARS-CoV-1 to health-care personnel in association with exposure to aerosol-generating procedures found a significantly increased odds ratio of 6.6.[1] Data from China and Europe estimated that up to 5%-10% of cases are HCWs who constitute frontline efforts against this virus.[5,6]

It has been rightly said that necessity is the mother of invention, just as the growing numbers of HCW deaths in many nations along with the ongoing clinician concerns and anxiety about safety had pushed us toward the invention of new devices to minimize the risk of exposure. One such novel device is the aerosol box (AB). First described by Dr. Lai Hsien-Yung, these devices typically consist of a transparent plastic cube covering a patient’s head and shoulders, with access holes for the intubating and sometimes additional holes for an assistant.[7,8] The concept is to merely provide a physical barrier between a highly infectious patient and HCWs.[8] Various boxes, such as the AB shield, airway respiratory containment system, intubation box, angled AB, and others made of plastic or fiber have blossomed over the period of the pandemic. They are useful for endotracheal tube (ETT) intubation, however might be difficult for manipulation during the procedure. Similarly, we designed two AB devices using transparent polycarbonate fiber during the first wave of the pandemic to reduce the risk to HCWs involved in managing a patient with an acute airway compromise in the emergency department (ED).

Despite there being few published research papers on the safety or efficacy of the AB, these devices are being used in clinical practice and manufacturers have already distributed hundreds of units to hospitals in the United States of America, the United Kingdom, and Australia.[9–12] This study was done to identify a device that helps in reducing cumulative viral exposure without compromising successful airway management.



This was a prospective observational study done for 7 months (October 20-April 21) on 143 patients presenting with an acute airway compromise to the ED.


This study was conducted in a 49-bedded ED of a large tertiary care center in South India, during the COVID-19 pandemic. During this period, the ED was structurally divided into two zones called COVID-19 suspect zone and green zone, respectively. The former was used to receive COVID-19 suspects and positive cases, while the latter was used for trauma or nonsuspect patients.


All adult patients (age more than 18 years) requiring emergency intubation in the ED during the study period were included in the study after obtaining informed written consent from the next of kin.

Exclusion criteria

Patients whose relatives did not consent for the study were excluded from the study.

Study size

The primary objective of the study was to assess the time taken for intubation (TTI) in a patient with AB as compared to intubating without an AB. The sample size was calculated based on a study done by Begley et al. and calculated using nMaster software version 2.0 (Department of Biostatics, Christian Medical College, Vellore, India).[11] This study required a total of 42 patients with 21 in each arm.

Study protocol

Two models of AB were compared. Both the boxes were cuboid-shaped transparent polycarbonate assemblies measuring 45 cm in height and width and 56 cm in breadth with 1 cm in thickness. AB I had an opening of 40 cm × 30 cm [Figure 1 – model I], whereas AB II had a smaller circular opening measuring 30 cm in diameter [Figure 1 – model II]. These AB were interchanged between COVID suspect zone and green zone every 30 days during the study period. Intubations done on patients without AB were taken as the control arm for the study.

Figure 1:
Figure representing box Aerosol box I and II

Endotracheal intubations were done by a total of 39 ED physicians who had at least 1 year of experience and previously performed a minimum of 30 intubations each. It was made sure that all the HCWs involved during the procedure were wearing appropriate personal protective equipment (PPE) according to the standard Centers for Disease Control and Prevention.[13] All intubations were performed as rapid sequence intubation using a video laryngoscope following the Difficult Airway Society guidelines.[14] An in situ simulation was conducted with best efforts to replicate the near to same scenario encountered by the ED physician, while intubating on a patient, a total of three intubations were performed by each physician in a mannequin using AB I, AB II, and without an AB so that our study can be compared with the other studies done across the world.

Outcome variables

The primary outcome was taken as TTI in a patient with and without AB. Secondary variables included first-pass success rate of AB I, AB II and no AB in patients and mannequins; TTI between AB I and AB II in patients and mannequins; TTI by physicians with more than 2 years’ experience and AB-related hindrance.


The data were subjected to selection bias due to the lack of randomization, but it was curtailed using the cross-over study design.

Statistical analysis

Data analysis was done using the Statistical Package for the Social Sciences (SPSS) for Windows software released 2015, version 23.0, Armonk, New York, USA. Median with interquartile range (IQR) and mean with standard deviation were used for continuous variables. Dichotomous variables were compared using the Chi-square test. The absolute difference between AB/no AB and AB I/AB II was calculated. Box plot analysis was used to compare the primary outcome between AB I/AB II/no AB and mannequin intubations. For all variables, P < 0.05 was deemed significant.

Ethical considerations

This study was approved by the Institutional Review Board before the commencement of the study; approval from the Institutional Review Board Ethical Committee was obtained (IRB Min no: 13162 dated July 22, 2020). Patient confidentiality was maintained using unique identifiers and password-protected data entry software with restricted users.


Our ED received a total of 36,121 patients during the study period of which 144 patients were included in the test arm. Among these, 59 patients were intubated with AB I and 85 patients were intubated with AB II. A separate set of 25 patients were recruited after the second wave of the COVID-19 pandemic. These patients were taken as control arms and were intubated without an AB [Figure 2].

Figure 2:
STROBE diagram

Baseline characteristics

Age varied between 46 and 48 in all the arms with a male predominance of more than 70%. The most common cause of airway compromise was trauma (45%), closely followed by features of severe acute respiratory illness (34%) in both arms. More than 90% of patients had Cormack–Lehane (CL) Grades 1-2. Difficult intubations included CL Grades 3-4 or any one of the LEMON criteria fulfillments. Lemon criteria fulfilling was 28.8% in AB I and 9.4% in AB II, implying that the percentage of difficult intubation was also found to be higher in the box I group compared to box 2. Whereas, when looking at the no box group, difficult intubation was encountered only in one case out of 25 patients. The baseline characteristics are given in Table 1.

Table 1:
Baseline characteristics using aerosol box I, aerosol box II, and no box

Primary and secondary outcomes

The overall time taken to intubate using any AB was 63 s with an 81.9% first-pass success (FPS) rate and that of AB I was 67 s with 76.3% FPS and AB II was 57 s with an 85.9% FPS rate. Whereas, intubations without an AB were done in 34 s with a 92% FSP rate. The box-and-whisker plot analysis of primary outcome (TTI) is demonstrated in Figure 3. Intubations done by physicians with more than 2 years’ experience were faster in both the AB and without AB arm when compared to intubations done by physicians with <2 years of experience. Among the study population, 23.7% of ED physicians felt that AB I caused hindrance during the procedure, whereas only 14% of the intubators felt that AB II was a hindrance during their procedure. Following these results, the box-and-whisker graph [Figure 3] plotted against the type of intubation adjunct versus TTI showed that irrespective of the model of the AB, the median TTI is much higher compared to the no AB and mannequin arm. The primary and secondary outcomes using AB versus no box and AB I versus AB II are given in Table 2.

Figure 3:
Box and Whisker plot analysis of primary outcome
Table 2:
Primary and secondary outcomes - aerosol box versus no box and aerosol box I versus aerosol box II

Systematic review

We did a systematic review of the available literature to assess the performance of the AB. A total of 22 studies were included in this review, of which 19 were performed on mannequins and 3 were done on patients. All studies provided data on TTI with and without an AB. Comparisons between the AB and no AB were analyzed using mean difference (MD). An estimation formula was used to convert median values to mean values with standard deviation to facilitate statistical analyses [Table 3].[11,15–35] Overall comparison of all the studies showed results on par with the results of our study, showing that the use of AB increased the TTI and decreased the FPS rate. Furthermore, those studies done by trained anesthetists showed a relatively lower mean TTI [Figure 4].

Table 3:
Meta-analysis of aerosol box studies (both patient and mannequin/simulation)[ 11 , 15–35 ]
Figure 4:
Forest plot analysis – A systematic review of aerosol box study


This study demonstrated a comparative analysis of two different models of AB used in a real-world scenario for endotracheal intubation during the COVID-19 pandemic in India. The key finding of our study was that the median duration of intubation done without the AB were much faster when compared to using one. Additionally, intubations done without AB had lower FPS rate.

Any device that is being introduced into clinical practice must undergo extreme scrutiny weighing all of its risks and benefits. Stabilization of the airway, especially in a highly intense setup like ED, is influenced by innumerable variables. Mishaps can lead to a disastrous outcome that can eventually lead to the loss of human lives. One such experimental device was the AB which has become increasingly popular during the COVID-19 pandemic. Although in situ simulations can predict the efficacy and performance of a device, when used in real life, several factors can influence the outcome, leading to a higher rate of failure. To our knowledge, this is the first study with such significant cohort participants that has been done in an Indian ED setup to assess the performance of AB in a real-world scenario.

In clinical practice, patients with severe COVID-19 infections suffer from critical hypoxia which necessitates a prolonged duration of preoxygenation before intubation or reoxygenation in case of failed intubation. Thus, the duration of intubation measured in our study only included the time duration of actual attempts of intubation. Interestingly, AB II which was assumed to be tougher owing to its small openings for the arms to maneuver inside required lesser time to intubate and had a better first-pass success rate when compared to AB I. In contrast, a prospective randomized noninferiority study comparing the time to intubate with and without the barrier box by Madabhushi et al. showed that there was no significant time difference in intubating with or without the box when done on normal airway patients without morbid obesity.[16]

In the real-world scenario, the median duration of intubation for AB I was longer when compared to AB II. However, when comparing the duration of intubation in physicians with more than 2 years of experience, it was observed that intubations were done at least 10 s faster when compared to intubations done by physicians with <2 years of experience. We feel that this difference in the overall duration of intubation can be attributed to the years of the intubator’s experience. Affirming the above statement, the overall multiple intubation attempts were mostly by physicians with <2 years of experience. A systematic review and meta-analysis done by Lim et al. on the impact of an AB on time to tracheal intubation showed results that the TTI was relatively shorter when intubation was performed by more experienced physicians which is consistent with our findings.[36]

We found no significant difference in the mean duration of intubation based on the physician’s years of experience in the in situ simulation. Whereas, in the real-world scenario, physicians with <2 years of experience took a long time to secure an airway. The difference in the duration of intubation between simulation and reality can be attributed to the fact that in an in situ simulation, there is less physician anxiety, no critically ill patients, or terrified relatives to deal with.

The FPS rate of both the models was significantly higher in simulation compared to the real-world scenario. In contradiction, the AB hindrance was reported more during the in situ simulation when compared to real-life practice. This can be elucidated due to increased awareness of AB by the intubator in simulation, whereas in practice, the intubator is more focused on securing the airway.

There was only a single event of a breach in PPE observed in our study which occurred with the model I AB. A study done by Begley et al. showed a much higher rate of a breach in PPE in comparison to this study.[11] This was possible because all ED physicians at our center were regularly updated and trained regarding the appropriate use of PPE and other COVID-19 management guidelines.

A randomized cross-over simulation study by Noor Azhar et al. showed that the use of AB significantly decreased the contamination of the PPE during aerosol-generating procedures.[37] In our study, all the physicians who participated in the study were followed up for 14 days after intubation, and none of the physicians was infected with COVID-19 infection during that period. However, there were other confounding factors associated with proper protection such as the N95 mask and face shield. It is beyond the scope of our study to unilaterally proclaim the efficacy of the AB against the risk of viral transmission.

Airway management in a stressful ED setup is merely more than placing an ETT; there are multiple associated factors about each patient that has to be considered and managed accordingly. The most commonly faced hurdles are oropharyngeal secretions, device fogging, critical hypoxia, patient repositioning, anxious relatives, etc. In critically ill patients it was arduous to prioritize the placement of the AB before intubation while simultaneously making sure there is no delay in airway management.

This is the first study that was done in a real-world ED scenario, thereby helping in assessing the performance of AB in clinical practice. Additionally, it also helped in figuring out difficulties faced by the physicians when dealing with an actual patient. The in situ simulation done acted as a control arm providing a clear comparison.


The primary limitation in our study was the small sample size, hence a logistic regression analysis was not feasible. Inferences that can be drawn from secondary outcomes were also not possible. All the intubations were done by ED physicians with training in airway management; however, we could not ensure uniform seniority among the intubators due to the burden of the ongoing pandemic leading to an ‘all hands-on deck’ scenario.


The use of an AB is associated with a longer TTI when compared to intubations done without an AB. TTI was relatively shorter when intubation was performed by more experienced emergency physicians. FPS rates were low with intubations done using AB.

Research quality and ethics statement

This study was approved by the Institutional Review Board/Ethics Committee at Christian Medical College and Hospital, Vellore, Tamil Nadu (IRB Min no: 13162 dated July 22, 2020). The authors followed the applicable EQUATOR Network ( guidelines, specifically the STROBE guidelines, during the conduct of this research project. We also certify that we have not plagiarized the contents in this submission and have done a plagiarism check. We also certify that none of the authors is a member of the Editorial Board of the Journal of Global Infectious Diseases.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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                                        Aerosol box; airway management; COVID-19; personal protective equipment; rapid sequence intubation; systematic review

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