Continuous positive airway pressure (CPAP) is the most effective treatment for obstructive sleep apnea (OSA). CPAP therapy is used to improve ventilation and gas exchange in the intensive care unit (ICU) and in the neonatal unit. In recent years, CPAP has also been used after surgery to prevent postoperative pulmonary complications. Worldwide, more than 310 million people undergo anesthesia and surgery each year and, in the developed countries, approximately 15%–20% of the patients suffer from postoperative complications.1,2 Postoperative pulmonary complications are common and include pneumonia and respiratory failure.3 Depending on the definition and surgical population, approximately 1%–40% of patients undergoing surgery suffer from postoperative pulmonary complications.3,4
“A rude awakening – the perioperative sleep apnea epidemic” was highlighted by Memtsoudis et al5 in 2013. OSA is a risk factor for postoperative respiratory failure, cardiovascular events, unplanned admission to ICUs, surgical site infections, and increased length of hospital stay.5–11 OSA is reported to worsen in the postoperative course, especially when high opioid doses are given.12–14 Unrecognized severe OSA is a risk factor for 30-day postoperative cardiovascular complications after major noncardiac surgery.15 OSA is common in the general population and in patients before surgery.16,17 In patients undergoing bariatric surgery, around 70% suffer from sleep apnea.18 Notably, most OSA patients are undiagnosed when entering the operating theater.19 Different risk scales, including the STOP-Bang screening questionnaire that is a sum of 8 positive answers to Snoring, Tiredness, Observed apnea, high blood Pressure, Body mass index >35 kg/m2, Age >50 years, Neck circumference >40 cm, and male Gender, are, therefore, commonly used for the opportunistic screening of OSA before surgery.20
Patients with OSA have recurrent episodes of apnea and hypopnea during sleep, accompanied by hypoxic events and surges of sympathetic activation. Obesity, retrognathic mandibulae, male sex, and age are associated with the risk of OSA.21,22 Patients seeking medical attention for OSA typically complain of snoring and daytime sleepiness, contrary to subjects with OSA from the population who are often asymptomatic.16,23
CPAP during sleep is the most effective and extensively used treatment of OSA.24,25 One problem is, however, the tolerance of and compliance with treatment, especially in subjects who do not experience any improvement in symptoms, that is, a reduction in daytime sleepiness. Side effects such as aerophagia and annoying mask leaks are related to the pressure that is given. Other side effects include nasal dryness and claustrophobia. Modern CPAP devices automatically titrate pressures to the minimum needed to abolish sleep apnea, which varies between individuals and with body and neck posture and sleep stage overnight. They are also humidified to reduce nasal side effects (Figure).
The American Society of Anesthesiologists (ASA) guidelines suggest sleep apnea investigations before surgery in patients at risk, followed by the treatment to reduce postoperative morbidity and mortality.26 Moreover, the Society of Anesthesia and Sleep Medicine (SASM) guidelines published in 2016 recommend that sleep apnea patients on CPAP should continue with treatment both preoperatively and postoperatively.27 CPAP use should be considered case by case in suspected but previously undiagnosed OSA.27 The perioperative implementation of CPAP demands knowledge and education that create familiarity with the device, which is excellently described by Hillman et al.28
In this review, we summarize current evidence regarding the effect of CPAP therapy on perioperative outcomes in the surgical population, with the emphasis on patients with OSA.
Trials of CPAP in adults in the perioperative period and studies published in English were included.
PubMed was searched from January 1980 until September 1, 2020 for studies of “Continuous positive airway pressure” and (postoperative or surgery) and (“randomized controlled trial” or “controlled clinical trial” or “systematic review”). The titles and abstracts of all the identified trials were first screened for relevance. Reference lists of all the identified trials and systematic reviews were checked to identify additional trials.
The search strategy resulted in 336 articles. Twenty-one relevant randomized controlled trials, comprising 2046 patients, were identified and included in this review (Tables 1 and 2), together with 1 systematic review with the emphasis on OSA (Table 2). Fourteen randomized controlled trials compared CPAP with standard care, including supplementary oxygen in the postoperative period (Table 1). Bilevel PAP was used in 1 trial,32 and 4 trials used auto-CPAP, commonly used for treating OSA attached to supplementary oxygen.37,46,48,49 Six trials investigated the effect of CPAP versus incentive spirometry, positive expiratory pressure therapy, or physical therapy.29,39–41,43,44
Table 1. -
Randomized Controls Trials on Perioperative CPAP
||Effect of CPAP
|Sah et al29
||3 arms:Incentive Spirometry: 5 times in 1 min and 5 min/hCPAP: 5 min/hControl oxygen: 6 h postoperative
||CPAP: 10 cm
|Guimarães et al30
||CPAP versus Venturi mask
||Boussignac CPAP: 5–8 cm
||Laparoscopic Roux-en-Y GBP
||2 h postoperative
||No effect on FEV1 and VC
|Zaremba et al31
||CPAP 1 h postoperative versus oxygen
||Oxygen-driven CPAP: 10 cm
||Reduced AHI, oxygen desaturations, mean oxygen saturation
||Reduced opioid-induced RD
|Al Jaaly et al32
||Time to discharge
2, FEV1 atelectasis, adverse events, duration of ICU and postoperative stay, and actual postoperative stay
||BiPAP: mean 16 h versus standard care
||BiPAP: 12/5, 17/10 For <24 h
||Reduced recovery time
|FEV1, ICU time unchanged
|Wong et al33
||Boussignac CPAP O2 of 15 L/min and CPAP pressure of 10 cm vs 40% O2 Venturi mask 1 h postoperative
||Boussignac CPAP: 10 cm
||No change in FEV1, FEVC
|Zarbock et al34
||Postoperative CPAP 6 h or prophylactic CPAP 10 min every q 4 h
||Nasal CPAP: 10 cm
|Gaszynski et al35
||CPAP versus oxygen alone
||Boussignac CPAP: 9.4 cm
||No change in Paco
|Squadrone et al36
||ICU and hospital LOS, pneumonia, sepsis, mortality
||Oxygen or oxygen plus CPAP
||CPAP: 7.5 cm
||Severe hypoxia after abdominal surgery
||Decreased the incidence of endotracheal intubation
|Drummond et al37
||Auto nasal CPAP versus usual care with oxygen
||Auto nasal CPAP: 5.5 cm
|Böhner et al38
||Postoperative pulmonary and cardiac complications
||CPAP the first night after surgery (12 h) versus standard care
||Nasal CPAP: 10 cm
||Midline laparotomy for vascular surgery
||Reduced severe hypoxia
|Fagevik Olsén et al39
||Incentive spirometry, 30 breaths/2 h or CPAP for 30 min/2 h for 3 d
||CPAP: 5–10 cm
||Thoracoabdominal esophageal cancer resections
||No effect on reintubation, gas exchange or spirometry
|Denehy et al40
||VC, FRC, or oxygen saturation on any of 4 postoperative days
||CPAP: 10 cm
||Upper abdominal surgery
||No difference in VC, FRC, or oxygen saturation on any of 4 postoperative days
|PT + CPAP
|For 15 or 30 min × 4/d for 3 d
|Matte et al41
||Lung function tests
||3 arms: incentive spirometry: 20/2 h; CPAP: 1 h/3 h; NIV-2P: 1 h/3 h
||CPAP: 5 cm; NIV-2P (BiPAP): 12/5
||Improved VC, FEV1, and Pao
2 POD 2
|Lindner et al42
||CPAP: 12 cm H2O Fio
2 = 2 35% during 3 h/d after extubation versus standard treatment
||CPAP: 12 cm via mouthpiece
||Upper abdominal surgery
||Higher VC and FRC in the CPAP group
|Ricksten et al43
||Postoperative radiological changes
||3 groups: CPAP, PEP, control: 30 breaths/h for 3 POD
||CPAP: 10–15 cm
||Upper abdominal surgery
||Lower (A-a) O2-diff POD 2, 3. No effect on PEF. Higher FVC POD3, reduced atelectasis
|Stock et al44
||3 arms: incentive spirometry, CPAP
||CPAP: 7.5 cm
||Upper abdominal surgery
||Coughing and deep breathing up to 3 d
|1–3 d postoperative
|Carlsson et al45
||CPAP with facemask during 4 h
||CPAP: 5–10 cm
||No difference in Pao
2 or VC
Abbreviations: AHI, apnea-hypopnea index; BiPAP, bilevel positive airway pressure; CABG, coronary artery bypass grafting; CPAP, continuous positive airway pressure; FEV1, forced expiratory volume during 1 second; FRC, functional residual capacity; FVC, forced vital capacity; GBP, gastric bypass; ICU, intensive care unit; LOS, length of stay; ODI, oxygen desaturation index; PAP, positive airway pressure; PEF, peak expiratory flow; PEP, positive endexpiratory pressure; POD, postoperative day; PT, physical therapy; RD, respiratory depression; VC, vital capacity.
Table 2. -
Randomized Controlled Trials and Systematic Reviews on Perioperative CPAP Use in Patients With a High Risk or a Diagnosis of OSA
||Effect of CPAP
|Nadler et al46
||Perioperative auto-CPAP versus routine
||Auto-CPAP preoperative and postoperative
||Elective hip or knee arthroplasty
||No effect on delirium
|OSA according to STOP-Bang
|Nagappa et al47
||Postoperative adverse eventsAHIHospital length of stay
||Preoperative or postoperative CPAP
||No difference in postoperative adverse events
|Lower AHI and trend toward shorter hospital length of stay with CPAP
|O’Gorman et al48
||Hospital length of stay
||Auto-CPAP: 10–15 cm versus standard care
||Elective hip or knee arthroplasty
|OSA according to Flemons score
|Liao et al49
||Auto-CPAP nights preoperative and 5 nights postoperative versus standard care
||Auto-CPAP preoperative and postoperative
||Mixed surgery (50% orthopedic)
||Reduced AHI and reduced oxygen desaturation index
|PSG diagnosis of OSA
|Neligan et al50
||FVC 24 h
||FEV1, FVC and PEF at 1 and 24 h postoperative complications
||Boussignac CPAP: 10 cm preoperative and postoperative
||Improved spirometry up to 24 h
|Immediately after extubation versus 30 min later
||PSG diagnosis of OSA
Abbreviations: AHI, apnea-hypopnea index; CPAP, continuous positive airway pressure; FEV1, forced expiratory volume during 1 second; FRC, functional residual capacity; FVC, forced vital capacity; GBP, gastric bypass; OSA, obstructive sleep apnea; ODI, oxygen desaturation index; PAP, positive airway pressure; PEF, peak expiratory flow; PSG, polysomnography; PT, physical therapy; STOP-Bang, Snoring, Tiredness, Observed apnea, high blood Pressure, Body mass index, Age, Neck circumference and Gender; VC, vital capacity.
The duration of CPAP treatment varied considerably. CPAP was given postoperatively for ≤1 hour in 6 studies29,31,33,39,40,50 for 2 hours in 1 study,30 for 3 hours in 1 study,42 for 4 hours in 1 study,45 and for ≥6 hours in 8 studies.32,35–38,46,48,49 Interestingly, a study by Squadrone et al36 focused on a subgroup of patients who had developed severe postoperative hypoxia.
Effect of CPAP on Patients With OSA
Four trials investigated the effect of CPAP on a total of 398 patients with a polysomnographic diagnosis or a high suspicion of OSA according to the STOP-Bang or Flemons score, mainly after orthopedic surgery (Table 2).46,48–50 Three trials used auto-CPAP46,48,49 and 1 trial used Boussignac CPAP 10 cm after laparoscopic bariatric surgery.50 All patients with OSA were newly diagnosed preoperatively, and they were naive to CPAP before the trials. Two trials reported a reduction in the apnea-hypopnea index (AHI) using auto-CPAP,46,49 while one of them also reported that oxygen saturation improved, with a reduction in the oxygen-desaturation index.49 One trial reported that lung function (forced vital capacity [FVC]) was better if Boussignac CPAP was initiated immediately after surgery in the operating theater versus half an hour later in the postanesthesia care unit.50 Auto-CPAP had no effect on postoperative delirium46 or hospital length of stay.48 Zaremba et al31 investigated the effect of 1 hour of CPAP after bariatric surgery in a patient cohort, where 64% had OSA. They reported a reduction in the AHI and oxygen desaturation index, as well as a reduction in respiratory depression in the postanesthesia care unit.31 Compliance with auto-CPAP was generally low after surgery in all 3 studies using auto-CPAP.46,48,49 Problems using CPAP included generalized discomfort, nausea, and vomiting after surgery.49 Many patients regarded CPAP as uncomfortable or intolerable.48
One systematic review including a total of 6 studies, including 2 of the aforementioned studies,48,49 did not find any difference in postoperative adverse events between the patients who had CPAP perioperatively and those who did not.47 The lack of difference in postoperative adverse events between the 2 groups could, however, be due to the small sample size of 900 patients included. In that review, the mean (standard deviation [SD]) AHI was reduced from 37 ± 19 events/h before surgery to 12 ± 16 events/h (P < .001) while using CPAP after surgery. There was also a trend toward a reduction in the hospital length of stay from 4.0 ± 4 in the CPAP group compared to 4.4 ± 8 days in the non-CPAP group (P = .05).47
Effect on Endotracheal Intubation, Pneumonia, and ICU Transfer
Squadrone et al36 studied the effects of CPAP in patients who developed severe hypoxia after open elective abdominal surgery. The application of CPAP for 6 hours in the ICU reduced the incidence of endotracheal intubation, pneumonia, infection, and ICU length of stay, but it did not affect the hospital length of stay.36 Another trial investigated the effect of postoperative prophylactic CPAP for 6 hours in 500 patients after cardiac surgery.34 CPAP improved arterial oxygen partial pressure and reduced the incidence of pulmonary complications including pneumonia, reintubation rate, and readmission to the ICU.
Effect on Oxygen Partial Pressure or Oxygen Saturation
Eleven trials had an outcome related to oxygen partial pressure or oxygen saturation after surgery. This outcome improved using CPAP versus oxygen in 7 of the most recent trials of CPAP use for 1–8 hours.30,31,33–35,38,49 In contrast, there was no improvement in oxygen partial pressure or oxygen saturation in the 3 oldest trials37,40,45 or in 1 trial using CPAP for only 5 minutes an hour.29
Effect on Lung Function
Seven studies had an outcome of vital capacity (VC), FVC, or forced expiratory volume during 1 second (FEV1). VC, FVC, or FEV1 improved in 2 trials41,42,50 and was unaffected by CPAP in 7 trials.30,32,33,39,40,43,45 One trial reported that FEV1, FVC, and peak expiratory flow (PEF) were better after 24 hours if obese patients received CPAP immediately after surgery versus after 30 minutes.50
Effect on Opioid-Induced Respiratory Depression
CPAP treatment for 1 hour immediately after bariatric surgery reduced opioid-induced respiratory depression in the postanesthesia care unit in a cohort of patients where 64% were diagnosed with OSA within the study.31
CPAP Versus Incentive Spirometry, Positive Expiratory Pressure, and Physical Therapy
CPAP was compared with incentive spirometry in 4 trials,29,39,41,44 with positive expiratory pressure breathing in 1 trial43 and with physical therapy in another trial.40 These studies focused on lung function and oxygen partial pressure as the outcome. One trial reported significantly improved VC and oxygen partial pressure after 1 hour of CPAP/3 h,41 while no difference was reported in the other trials.
Adverse Effects of CPAP
Serious complications are uncommon with CPAP, and we did not identify any such serious complications in our research.
Aerophagia is common in sleep apnea patients on CPAP therapy and is related to the presence of nighttime gastroesophageal reflux.51,52 This risk increases with higher CPAP pressure. Auto-CPAP, which continuously titrates delivered pressures to deliver the minimum required to maintain airway patency, reduces the symptoms of aerophagia, while not affecting compliance when compared with standard CPAP therapy.53 Claustrophobia while using CPAP was reported in 9% in 1 trial.38 Nasal dryness is common. Most modern auto-CPAP devices incorporate a humidifier to help address the problems of nasal side effects.
We identified 21 randomized, controlled trials of the effect of CPAP on postoperative outcomes, including the occurrence of endotracheal intubation with mechanical ventilation, pneumonia, oxygen partial pressure, AHI, oxygen desaturation index, lung function, delirium, and length of stay. Only 4 randomized, controlled trials and 1 systematic review investigated patients with OSA, naive to CPAP. No study was found investigating the effect of CPAP exclusively among patients experienced with its use, through their use of it at home to treat previously diagnosed OSA.
All OSA patients reduced their AHI with postoperative CPAP use and, in the studies that included the oxygen desaturation index, that parameter was also reduced. In a recent systematic review, postoperative adverse events were not reduced although the AHI was attenuated.47 In a recent expert consensus meeting on the perioperative care of OSA patients undergoing bariatric surgery, it was stated that there was a very low quality of evidence for the perioperative use of CPAP in OSA patients with an AHI of ≥15 undergoing bariatric surgery.54 Despite this, there was a full consensus that perioperative CPAP use should be recommended in this patient group. This highlights the need for larger multicenter studies in this surgical high-risk cohort, since, as we demonstrate, there are only a handful of randomized, controlled studies investigating the effect of the perioperative use of CPAP in OSA patients.
Seven of the most recent trials reported that CPAP improves oxygen partial pressure after surgery.30,31,33–35,38,49 Two trials reported that CPAP reduces the AHI and the oxygen desaturation index. Interestingly, 2 trials reported that the improvement in oxygen partial pressure reduced the need for endotracheal intubation and mechanical ventilation after surgery.34,36 One of these trials involved patients with severe hypoxia,36 while the other trial comprised patients with CPAP after heart surgery.34 The common denominator in both these studies is that they applied the CPAP postoperatively for 6 hours.34,36 From a physiologic standpoint, it seems logical that a longer duration of CPAP postoperatively would have a greater effect, compared with shorter periods postoperatively or preoperatively.29
One study investigated the effect of CPAP on hospital length of stay and another study investigated its effects on the occurrence of postoperative delirium, without any benefit being demonstrated. Two trials reported improvements in ventilatory capacity (ie, VC), while 7 other studies did not.
Patients undergoing surgery without daytime sleepiness often experience problems with tolerance of and compliance with CPAP, and they often have very poor adherence to CPAP therapy.55 The problem associated with tolerance of CPAP after surgery was also reported in the 3 trials using auto-CPAP on patients with OSA, naive to CPAP. Adherence to CPAP treatment is a multifaceted problem including patient-, treatment-, condition-, social-, and health care–related factors. Knowledge of facilitators and barriers to adherence to CPAP treatment can be used in interventional strategies.56 These results should encourage future investigations to determine barriers to CPAP adherence in the perioperative period.57
In 2014, Cochrane published a systematic review of “Continuous Positive Airway Pressure (CPAP) During the Postoperative Period for Prevention of Postoperative Morbidity and Mortality Following Major Abdominal Surgery” based on 10 randomized, controlled trials.24 They concluded that there was “very low-quality evidence” that CPAP initiated during the postoperative period might reduce postoperative atelectasis, pneumonia, and reintubation, but its effect on mortality, hypoxia, or invasive ventilation are uncertain. Compared with the Cochrane review, we included 21 randomized, controlled trials in this review despite excluding 2 trials reviewed by Cochrane. Contrary to Cochrane, we report that postoperative oxygen saturation is improved by using CPAP. Cochrane included 1 trial reporting a reduction in invasive ventilation after surgery, while we included 2 such studies.
In 2008, Ferreyra et al58 conducted a meta-analysis of the effect of CPAP therapy on respiratory complications after abdominal surgery. The meta-analysis included 9 trials of which 8 are included in this review, with 1 excluded because it was in German. In the meta-analysis, CPAP was associated with a lower rate of postoperative pulmonary complications compared with the standard treatment, with a risk reduction of 0.34 (95% confidence interval [CI], 0.15-0.48). Furthermore, CPAP was associated with a reduction in atelectasis with a risk ratio of 0.25 (95% CI, 0.03-0.42) compared with the standard treatment and was also associated with a reduction in pneumonia with a risk ratio of 0.67 (95% CI, 0.25-0.86).58
Patients with existing CPAP treatment for OSA are strongly recommended to use CPAP during the perioperative period.26,27,54 However, no study investigating the effect of CPAP treatment in the perioperative period in these patients was identified. The effects on postoperative use and on complications in these patients with previously prescribed CPAP for OSA are therefore unknown, and as a result, there is a knowledge gap. Other gaps include the effect of CPAP on surgical and cardiovascular complications after surgery.
Several problems are involved with future studies using CPAP on postoperative complications. Further thought is also required regarding the effects of CPAP on postoperative complications, particularly given the adherence problems experienced by patients naive to the therapy, which limits its application. Methods of improving adherence through equipment design modifications and staff training in its use are aspects worthy of future study. Using patient-related outcomes includes the need for large studies. We therefore recommend international multicenter trials with the emphasis on methods for improving CPAP adherence, including autotitration, humidification, and staff training in its application.
CPAP after surgery improves oxygenation and reduces the need for reintubation and mechanical ventilation after surgery. It is also evident that CPAP reduces apnea frequency and related oxygen desaturations after surgery. Poor adherence to CPAP in the perioperative setting is a limiting factor in assessing its potential to optimize postoperative cardiorespiratory outcomes. Studies of postoperative outcomes in patients who have previously been prescribed CPAP for OSA and are therefore familiar with its use could help to address this shortcoming. These studies are, however, still lacking.
Name: M. Jonsson Fagerlund, MD, PhD.
Contribution: This author helped in the conception and design, acquisition, analysis, or interpretation of the data, drafting of the manuscript, critical revision of the manuscript for important intellectual content, and final approval of the submitted manuscript.
Conflicts of Interest: M. J. Fagerlund has received lecture fees and travel support from Fisher & Paykel Healthcare (Auckland, New Zealand) and has a contract as a consultant with MSD.
Name: K. A. Franklin, MD, PhD.
Contribution: This author helped in the conception and design, acquisition, analysis or interpretation of the data, drafting of the manuscript, critical revision of the manuscript for important intellectual content, and final approval of the submitted manuscript.
Conflicts of Interest: None.
This manuscript was handled by: Toby N. Weingarten, MD.
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