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Featured Articles: Special Article

Perioperative Lung Protection: General Mechanisms and Protective Approaches

Ball, Lorenzo MD, PhD*,†; Almondo, Chiara MD*; Pelosi, Paolo MD, FERS*,†

Author Information
doi: 10.1213/ANE.0000000000005246

Abstract

See Article, p 1663

Postoperative pulmonary complications (PPCs) are one of the most important cause of perioperative morbidity and mortality in patients undergoing noncardiothoracic surgery, and their occurrence is associated with increased hospital length of stay and mortality.1–3 Their incidence ranges from 2% to 40%, due to the high heterogeneity of surgical populations and definitions adopted across studies.4 Recently, task forces attempted to propose an accepted definition of PPCs.5,6

PPCs may origin from several patient-, surgery-, and anesthesia-related factors.7 Mechanical ventilation itself, an unavoidable supporting tool during general anesthesia, may cause ventilation-induced lung injury, which mediates the development of pneumonia, atelectasis, respiratory failure, and worsening of lung function.8–10 In the perioperative period, other factors contribute to the lung injury, as anesthetic and analgesic drugs promoting the release of inflammation and bronchoconstriction mediators, altered mucociliary function, impaired surfactant production, and macrophage function promoting retention of secretions.11,12 Moreover, general anesthesia and postoperative pain may promote the onset of atelectasis through decreased inspiratory muscle tone and reduction of functional residual capacity, impacting gas exchange.13,14 More recently, it has been underlined that the reduction in end-expiratory lung volume is not only associated with atelectasis but also airway closure. When the end-expiratory lung volume is lower than airway closure volume, peripheral airways collapse and might promote lung injury in the alveoli, capillaries, and extracellular matrix.15

One of the aims of physiotherapy programs in the pre- and postoperative period is the prevention of PPCs and their associated burden of care. Intraoperative lung-protective strategies comprise the use of low tidal volume (TV), with or without positive end-expiratory pressure (PEEP) and alveolar recruitment maneuvers (ARM).16–18 Moreover, the postoperative use of respiratory assistance techniques including high-flow nasal cannulas (HFNC), continuous positive airway pressure (CPAP), and noninvasive ventilation has gained popularity as a strategy to prevent or treat PPCs.4

The principal purpose of this review is to provide an overview of the perioperative lung protection strategies in patients undergoing elective noncardiothoracic surgery, informing clinicians on evidence-based perioperative care pathways focusing on areas with greater clinical and research interest. We also conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) in noncardiothoracic surgery, focusing on the following aspects: preoperative physiotherapy, preoxygenation, intraoperative mechanical ventilation, postoperative prophylactic CPAP or HFNC, and postoperative physiotherapy.

METHODS

Literature Search and Study Selection

A systematic computerized search of the literature, until August 2020, was performed in the Cochrane Central Register of Controlled Trials, Literature Analysis and Retrieval System Online (MEDLINE), and Excerpta Medica dataBASE (EMBASE) electronic databases. Details on the search strategy are provided in Supplemental Digital Content, Document, https://links.lww.com/AA/D217. The following criteria for study eligibility were used: (1) RCTs comparing strategies of preoxygenation, preoperative physiotherapy, intraoperative ventilation or postoperative prophylactic CPAP, HFNC, and physiotherapy in surgical patients; (2) adult patients >18 years old; (3) patients undergoing general anesthesia; (4) English language; (5) specific postoperative lung injury outcomes reported, either as collapsed end point or atelectasis or pneumonia. We excluded (1) trials of patients undergoing cardiothoracic surgery; (2) trials that did not report the outcomes of interest; (3) case report, reviews, observational studies; (4) pediatric and neonatal studies. A primary search was conducted by 2 investigators (L.B. and C.A.) who verified the adherence to the inclusion criteria. Data extraction was performed independently by 2 authors (L.B. and C.A.), and discrepancies were solved by consensus. The primary outcome was the occurrence of PPCs, either reported as a collapsed endpoint or as the incidence of pneumonia or atelectasis.

Data Synthesis and Analysis

We conducted a meta-analysis when the clinical homogeneity of interventions was judged sufficient for pooling data from different RCTs. For dichotomous outcomes, we computed the relative risks (RRs) with their 95% confidence intervals (CIs). All estimates were calculated with a mixed-effects model using the DerSimonian-Laird method. Potential bias for the primary outcome was examined by a funnel plot of treatment effect versus study precision. Subgroups were compared with the Cochran’s Q test and residual heterogeneity assessed with the I2 statistics and Q test. We conducted a metaregression to investigate the role of intraoperative TV reduction and PEEP increase in reducing the incidence of PPCs. We performed the statistical analysis using R (R Foundation for Statistical Computing, Vienna, Austria) with the metafor and meta packages. Statistical significance was considered for 2-tailed P < .05.

RESULTS

Figure.
Figure.:
Summary of findings of the meta-analysis. ARM indicates alveolar recruitment maneuvers; CI, confidence interval; CPAP, continuous positive airway pressure; HFNC, high-flow nasal cannula; NA, not applicable; PEEP, positive end-expiratory pressure; TV, tidal volume.

The study inclusion flow is reported in Supplemental Digital Content, eFigure 1, https://links.lww.com/AA/D217. The analysis was divided into pre-, intra-, and postoperative periods, further stratified according to the type of intervention. The overall results of the meta-analyses are reported in the Figure.

Preoperative Interventions

We found 4 RCTs19–22 testing different concentrations of oxygen or the use of positive-pressure preoxygenation at induction (Table 1). We did not include these studies in a formal meta-analysis for the heterogeneity of outcomes and lack of major postoperative outcomes. Two studies demonstrated that preoxygenation with CPAP plus intraoperative PEEP reduced atelectasis compared to conventional preoxygenation and no intraoperative PEEP.21,22 Two studies reported that preoxygenation with a higher fraction of inspired oxygen (Fio2) increased the size of atelectasis,19,20 but allowed a longer time before desaturation during intubation.19

Table 1. - Characteristics of Studies Comparing Preoperative Lung-Protective Strategies
Study Type of Surgery Study Population Intervention Group Control Group Outcomes of Interest Main Findings
N Intervention N Intervention
Coussa et al (2004)21 Bariatric Morbidly obese patients, ASA II or III, aged 20–65 9 Preoxygenation with CPAP at 10 cm H2O for 5 min, intraoperative PEEP 9 Conventional preoxygenation, ZEEP Atelectasis
Oxygenation
Preoxygenation with CPAP and intraoperative PEEP reduced atelectasis formation and improved oxygenation
Edmark et al (2003)19 Gynecological ASA I–II, nonobese females scheduled for elective hysterectomy 24 Preoxygenation with 60% (N = 12) or 80% (N =12) oxygen 12 Preoxygenation with 100% oxygen Atelectasis
Time to desaturation during intubation
Increased atelectasis with 100% oxygen
Shorter time to desaturation with both 60% and 80% oxygen
Edmark et al (2011)20 Gynecological ASA I–II, females scheduled for elective hysterectomy or minor surgery 18 Preoxygenation with 60% (N = 8) or 80% (N = 8) oxygen for 5 min before anesthesia induction 9 Preoxygenation with 100% oxygen Atelectasis Increased atelectasis with higher concentrations of oxygen
Rusca et al (2003)22 Major abdominal ASA I–II, nonobese, scheduled for elective surgery 8 Preoxygenation with CPAP at 6 cm H2O, intraoperative PEEP 8 Conventional preoxygenation, ZEEP Atelectasis Preoxygenation with CPAP and intraoperative PEEP reduced atelectasis also at high fraction of inspired oxygen
Abbreviations: ASA, American Society of Anesthesiologists; CPAP, continuous positive airway pressure, PEEP, positive end-expiratory pressure, ZEEP, zero end-expiratory pressure.

Table 2. - Characteristics of Studies Comparing Preoperative Physiotherapy Strategies
Author Type of Surgery Intervention Group Control Group Outcome of Interest Main Findings
N Intervention N Intervention
Roukema et al (1988)23 Upper abdominal 69 Chest physiotherapy with education initiated in the preoperative period and continued postoperatively: diaphragmatic breathing, deep breathing, forced expiration, and coughing 50 No physiotherapy PPC Preoperative chest physiotherapy reduced the incidence of PPC
Condie et al (1993)24 Abdominal 158 Chest physiotherapy with education initiated in the preoperative period and continued postoperatively: lateral costal and diaphragmatic breathing exercises, huffing and coughing, with wound support 12 No physiotherapy PPC Preoperative chest physiotherapy did not reduce the incidence of PPC
Fagevik Olsén et al (1997)25 Abdominal 174 Chest physiotherapy initiated in the preoperative period and continued postoperatively: breathing with pursed lips, huffing and coughing, and information about the importance of early mobilization. High-risk patients also received resistance training with mask 52 No physiotherapy PPC Preoperative chest physiotherapy reduced the incidence of PPC
Chumillas et al (1998)26 Upper abdominal 40 Chest physiotherapy initiated in the preoperative period and continued postoperatively: forced expiration, coughing, maximal inspiration sustained for 3–5 s, chest expansion exercises, and diaphragmatic mobilization 41 No physiotherapy PPC Decrease of postoperative radiological alterations in moderate and high-risk patients, no incidence on PPCs
Dronkers et al (2008)27 Aortic 10 Inspiratory muscle training program for at least 2 wk before surgery 10 No physiotherapy Atelectasis No statistically significant improvement on atelectasis
Dronkers et al (2010)28 Abdominal oncological 22 Comprehensive physiotherapy: inspiratory muscle training plus aerobic training 20 No physiotherapy PPC Improvement of respiratory function, no effect on PPCs
Barbalho-Moulim et al (2011)29 Open bariatric 15 Inspiratory muscle training program for at least 2 weeks before surgery 17 No physiotherapy PPC Increased inspiratory muscle strength but no effect on PPCs
de Toledo Piza Soares et al (2013)30 Upper abdominal 16 Comprehensive physiotherapy: stretching exercises, trunk rotation, deep breathing, respiratory muscle training, active upper and lower extremity exercises, walking, and relaxation and guidance and training on coughing and huffing 16 No physiotherapy PPC Improved respiratory function but no effect on PPCs
Dunne et al (2016)31 Liver resection 19 Comprehensive physiotherapy: warm-up and warm-down, training using a cyclo-ergometer 15 No physiotherapy Pneumonia Improved respiratory function but no effect on PPCs
Abdelaal et al (2017)32 Laparoscopic upper abdominal 26 Comprehensive physiotherapy: 2 physical therapy sessions per week in the form of stretching exercises, trunk rotation, active upper and lower extremity exercises, walking and relaxation, respiratory muscle training, walking 24 No physiotherapy PPC Reduced incidence of PPC
Barberan-Garcia et al (2018)33 Abdominal 62 Comprehensive physiotherapy: warm-up, warm-down, cyclo-ergometer stationary bicycle at variable intensity 63 No physiotherapy PPC Improved respiratory function but no effect on PPCs
Boden et al (2018)34 Upper abdominal 218 30 min physiotherapy education and breathing exercises in a single session 214 No physiotherapy PPC Decreased PPC in intervention group
Valkenet et al (2018)35 Esophageal 120 Inspiratory muscle training 121 No physiotherapy Pneumonia Preoperative inspiratory muscle training did not reduce the incidence of pneumonia
Guinan et al (2019)36 Esophageal 28 Inspiratory muscle training 32 No physiotherapy PPC Preoperative inspiratory muscle training did not reduce the incidence of PPC
Abbreviation: PPCs, postoperative pulmonary complications.

We found 14 RCTs23–36 investigating the implementation of different preoperative physiotherapy and training regimens (Table 2). In 4 studies, physiotherapy was continued also in the postoperative period.23–26 On a total population of 1980 patients, preoperative physiotherapy reduced the incidence of PPCs (RR, 0.49, 95% CI, 0.35-0.69, P < .01 forest plot in Supplemental Digital Content, eFigure 2, https://links.lww.com/AA/D217, funnel plot in Supplemental Digital Content, eFigure 3 https://links.lww.com/AA/D217), but there was substantial heterogeneity (I2 = 65%, P < .01). We classified as comprehensive physiotherapy any strategy comprising several physical training activities not limited to the respiratory muscles. Stratification according to the type of intervention reduced heterogeneity and showed that all physiotherapy regimens were associated with a lower incidence of PPCs, except inspiratory muscle training alone (RR, 0.89, 95% CI, 0.58-1.38, P = .61).

Intraoperative Interventions

We pooled 5268 patients included in RCTs comparing intraoperative ventilation strategies. The characteristics of the studies are summarized in Supplemental Digital Content, eTable 1, https://links.lww.com/AA/D217: we found 3 studies37–39 comparing PEEP increase plus ARM plus TV reduction to conventional ventilation, 5 studies40–44 comparing PEEP increase plus ARM to conventional ventilation with same TV size, and 3 studies45–47 comparing TV reduction at the same PEEP level. Two studies compared >2 interventions41,44 and only 2 arms from each study were included in the meta-analysis (details provided in Supplemental Digital Content, eTable 1, https://links.lww.com/AA/D217). As illustrated in Supplemental Digital Content, eFigure 4, https://links.lww.com/AA/D217 (funnel plot in Supplemental Digital Content, eFigure 5, https://links.lww.com/AA/D217), the combination of PEEP increase, ARM, and TV reduction resulted in a lower incidence of PPCs (RR, 0.61, 95% CI, 0.39-0.94, P = .02). The appearance of PPCs was not different in patients who received lower compared to higher TV in trials without concomitant changes in PEEP (RR, 0.90, 95% CI, 0.62-1.32, P = .59). Also, the incidence of PPCs was similar in patients receiving higher PEEP plus ARM versus lower PEEP (RR, 1.03, 95% CI, 0.93-1.15, P = .51). At the metaregression analysis, we observed no association between the incidence of PPCs and the magnitude of TV reduction (β = .02, 95% CI, 0.16-0.20, P = .45) or PEEP increase (β = .02, 95% CI, 0.03-0.06, P = .75), but their interaction was significant (β = .03, 95% CI, 0.06-0.01, P = .016), suggesting that TV reduction acts differently when used in conjunction with PEEP changes. The reporting of other outcomes, including extrapulmonary complications, was too heterogeneous, and we decided not to perform a formal meta-analysis.

Postoperative Interventions

We found 7 RCTs48–54 investigating physiotherapy regimens administered in the postoperative period only (Table 3). On a total of 1531 patients (Supplemental Digital Content, eFigure 6, https://links.lww.com/AA/D217, funnel plot in Supplemental Digital Content, eFigure 7, https://links.lww.com/AA/D217), there was no effect association between the use of postoperative physiotherapy alone versus no physiotherapy and the incidence of PPCs (RR, 0.89, 95% CI, 0.69-1.16, P = .40). Stratification, according to the type of intervention (chest physiotherapy versus incentive spirometry), did not change the results (Figure).

Table 3. - Characteristics of Studies Comparing Postoperative Physiotherapy Strategies
Author Type of Surgery Intervention Group Control Group Outcome of Interest Main Findings
N Intervention N Intervention
Morran et al (1983)48 Gallbladder 51 Chest physiotherapy: breathing exercises with assisted coughing and vibration of the chest wall 51 No physiotherapy PPC No reduction of PPCs
Celli et al (1984)54 Abdominal 42 Incentive spirometry 44 No physiotherapy PPC Decreased incidence of PPCs
Hall et al (1991)51 Abdominal 431 Incentive spirometry 445 No physiotherapy PPC No reduction of PPCs
Mackay et al (2005)49 Open abdominal 29 Chest physiotherapy (deep breathing and coughing) 21 No physiotherapy (early mobilization alone) PPC No reduction of PPCs
Silva et al (2013)50 Open upper abdominal 28 Chest physiotherapy (deep breathing exercises) 28 No physiotherapy (early mobilization alone) PPC No reduction of PPCs
Lunardi et al (2015)52 Upper abdominal 67 Incentive spirometry 70 No physiotherapy PPC No reduction of PPCs
Pantel et al (2017)53 Bariatric 112 Incentive spirometry 112 No physiotherapy PPC No reduction of PPCs
Abbreviation: PPCs, postoperative pulmonary complications.

We found 7 studies41,55–59 investigating the role of prophylactic postoperative CPAP (Table 4). We pooled data from 1028 patients (Supplemental Digital Content, eFigure 8, https://links.lww.com/AA/D217, funnel plot in Supplemental Digital Content, eFigure 9, https://links.lww.com/AA/D217), observing that postoperative CPAP was associated with a lower incidence of PPCs (RR, 0.53, 95% CI, 0.30-0.94, P = .029). Heterogeneity was moderate (I2 = 44%, P = .11). However, when a large study that used CPAP with a mixed early therapeutic/prophylactic intention,59 the association was no longer significant (Figure, Supplemental Digital Content, eFigure 8, https://links.lww.com/AA/D217).

Table 4. - Characteristics of Studies Comparing Postoperative CPAP
Study Type of Surgery Study Population Intervention Group Control Group Outcomes of Interest Main Findings
N Intervention N Intervention
Squadrone et al (2005)59 Abdominal Patients with Pao 2/Fio 2 < 300 mm Hg postextubation 104 Fio 2 0.5, CPAP 7.5 cm H2O 105 Venturi mask at an Fio 2 0.5 Pneumonia CPAP reduced intubation rate
Denehy et al (2001)57 Upper abdominal 32 CPAP 10 cm H2O 4 times per day plus conventional physiotherapy 18 Conventional physiotherapy alone PPC CPAP did not significantly affect physiological or clinical outcomes
Ferrando et al (2018)41 Abdominal Two arms of a larger RCT 244 CPAP 5 or 10 cm H2O according to the body mass index 244 Venturi mask PPC (aspiration pneumonitis, bronchospasm, pleural effusion, atelectasis, hypoxemia, pneumothorax, pneumonia, ARDS) CPAP did not reduce PPCs
Böhner et al (2002)58 Vascular Patients receiving midline laparotomy for elective vascular surgery 99 Fio 2 0.4, CPAP 10 cm H2O for 12 h 105 Venturi mask Pneumonia
Severe hypoxia
CPAP improved oxygenation but did not reduce PPCs
Lindner et al (1987)56 Abdominal 17 CPAP 12 cm H2O Fio 2 0.35
3 h per day for 5 d plus conventional physiotherapy
17 Conventional physiotherapy alone Atelectasis CPAP reduced atelectasis
Stock et al (1985)55 Upper abdominal Elective upper abdominal surgery 23 CPAP 7.5 cm H2O for 15 min, every 2 waking hours, for 4–72 h 20 Incentive spirometry only Atelectasis CPAP reduced atelectasis
Abbreviations: ARDS, acute respiratory distress syndrome; CPAP, continuous positive airway pressure; Fio2, fraction of inspired oxygen; PPCs, postoperative pulmonary complications; RCT, randomized controlled trial.

A single study60 investigated the prophylactic use of HFNC in the postoperative period in noncardiothoracic surgery, suggesting no reduction in the incidence of PPCs (RR, 0.88, 95% CI, 0.70-1.11, P = .30).

DISCUSSION

In the present review and meta-analysis, we aimed to compare evidence of treatment effects for PPC management and whether benefits are associated with each treatment.

The main outcomes are (1) preoxygenation with CPAP improves oxygenation, and the use of higher Fio2 might increase atelectasis formation but increases the time to desaturation; (2) physiotherapy regimens initiated in the preoperative period are associated with a reduced incidence of PPCs; (3) intraoperative protective mechanical ventilation has a heterogeneous impact on PPCs in different trials, and the importance of TV reduction and PEEP increase remains uncertain; (4) physiotherapy initiated in the postoperative period only is not associated with reduced incidence of PPCs; (5) CPAP and HFNC used as prophylactic measures in the postoperative period offer limited benefit.

Compared to previous reviews and meta-analyses, we included recent studies on the role of physiotherapy, intraoperative mechanical ventilation, and noninvasive prophylactic respiratory support on PPCs. We focused the analysis on clinical postoperative outcomes and not on the physiologic response to treatments, and we restricted the analysis to noncardiothoracic surgery, which we think contributed to the robustness of our findings.

Preoperative Lung Protection

Most studies focusing on the preoperative period included in this analysis had a limited sample size, and the interventions were clinically heterogeneous. Concerning preoxygenation, our review of the literature suggests that positive-pressure preoxygenation with CPAP or PEEP plus manual ventilation or pressure support should be considered, especially in patients at high risk of desaturation, such as obese. The use of lower Fio2 at induction offers limited benefits in terms of the formation of atelectasis at the price of increasing the risk of desaturation and reducing the time-window for safe intubation. Moreover, recent studies challenge the actual contribution of Fio2 to the development of postoperative atelectasis.61 These concepts are being adopted by several national guidelines.62,63 Physiotherapy seems a simple, cheap, and cost-effective means to improve respiratory outcomes in patients undergoing noncardiothoracic surgery. In our analysis, we observed that preoperative physiotherapy, delivered with different techniques, seems effective, but there was a high heterogeneity of techniques involved. These findings are in line with recent meta-analyses.64,65 We identified studies performing chest physiotherapy as different combinations of deep breathing, diaphragmatic breathing, coughing, postural exercises, resistance training with mask. In other studies that we classified as “comprehensive physiotherapy,” several exercises were bundled, often including whole-body aerobic activity. The association with reduced incidence of PPCs was only observed for physiotherapy regimens that were initiated in the preoperative phase, continued or not in the postoperative phase. In a group of these studies, the patient was also supervised and assisted in the execution of physiotherapy postoperatively; in other studies, the patient performed postoperative exercises autonomously after having received preoperative training. Both approaches seemed to be associated with a reduced incidence of PPCs, with the exception of studies in which the intervention was based on inspiratory muscle training only, not combined with other procedures. Of notice, a large RCT reported the efficacy of a single preoperative physiotherapy and training session34 in preventing PPCs. Recently, there has been an increased interest in multimodal prehabilitation, an approach combining preoperative physical training with nutritional, psychological, and multidisciplinary counseling. However, a recent randomized trial questioned the validity of a multimodal prehabilitation program, compared to postoperative rehabilitation alone.66 Our analysis suggests that chest physiotherapy might be used to reduce PPCs when applied both in the preoperative and postoperative periods. Conversely, more complex physiotherapy approaches might be beneficial also if applied in the preoperative period only.

Intraoperative Lung Protection

This topic has been extensively discussed by Hol et al67 in this issue of Anesthesia& Analgesia. A large RCTs in 2013 compared PEEP plus ARM and low TV versus no PEEP and high TV, finding an important reduction in PPCs.37 However, no benefits were observed when 2 PEEP levels were tested at the same protective TV.42,43 These findings were generally interpreted as a call to use low TVs, with the effects of PEEP being more debated.68,69 However, a recent RCT on 1236 patients47 compared 2 strategies of low versus moderate TV (6 vs 10 mL/kg predicted body weight) in patients undergoing open and laparoscopic major surgery with an expected duration of >2 hours. Both arms received a fixed PEEP level of 5 cm H2O, a value that is intermediate between the levels used in the 2 previous largest RCTs.37,42 The incidence of PPCs was not different in the 2 groups, but there was a nonsignificant trend favoring low TV in laparoscopic surgery, but the study was not powered for this specific subanalysis. This study, included in the present meta-analysis, suggests that the advantages of low TV are less marked when a moderate PEEP level is used. Overall, the results of our meta-analysis and metaregression suggest that TVs between 6 and 10 mL/kg of predicted body weight could be tolerable, carefully titrated on the predicted body weight, but maintaining lower TVs might be warranted in specific subpopulations. In line with previous recommendations, higher TV should be avoided.69

Postoperative Lung Protection

In postoperative time, hypoxemia can complicate approximately 30% of the abdominal surgical procedures.59 Our meta-analysis shows unclear benefits of postoperative CPAP, HFNC, and physiotherapy applied with prophylactic intention, that is, in patients who did not already develop a PPC. The only postoperative physiotherapy regimens that reduced PPCs in our analysis were those initiated in the preoperative period. However, when hypoxia develops, the administration of oxygen should be done with positive-pressure devices, easily applicable at the bedside. In this context, CPAP seems to have the most promising role for its ease of use, availability, and efficacy in treating postoperative respiratory failure.59 In our analysis, we included in the meta-analysis on prophylactic CPAP, a study using CPAP as a mixed preventive/curative strategy.59 This study was also included in a Cochrane meta-analysis with aims similar to ours70; however, when we excluded this study, the associations between the use of CPAP and reduced incidence of PPCs were no longer observed.

The role of HFNC in abdominal surgery appeared uncertain, but these devices could play a role, as demonstrated in cardiothoracic surgery.71 Noninvasive bilevel ventilation was also used successfully to treat postoperative hypoxemia,72 but its administration requires a ventilator and trained personnel.

CONCLUSIONS

Lung-protective strategies should be considered throughout the entire perioperative period. Physiotherapy and patient training should be initiated in the preoperative phase, preoxygenation, and intraoperative protective mechanical ventilation should be titrated on an individual basis taking into account all the available evidence. The prophylactic use of strategies initiated in the postoperative period only, such as physiotherapy, CPAP, or HFNC, offers limited benefits. However, when the respiratory function deteriorates in the postoperative period, several noninvasive respiratory techniques should be considered to avoid reintubation and improve clinical outcomes.

DISCLOSURES

Name: Lorenzo Ball, MD, PhD.

Contribution: This author helped in review conception, literature review, statistical analysis, drafting and revising the manuscript.

Name: Chiara Almondo, MD.

Contribution: This author helped in literature review, data extraction, drafting and revising the manuscript.

Name: Paolo Pelosi MD, FERS.

Contribution: This author helped in review conception, critical review, editing and revising the manuscript.

This manuscript was handled by: Markus W. Hollmann, MD, PhD.

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