Only 2 studies, by Liao et al.20 and Rennotte et al.,40 reported on preoperative and postoperative AHI in patients using CPAP treatment (Table 5). One hundred patients received CPAP before surgery, and 51 patients continued CPAP in the postoperative period. The preoperative baseline AHI without CPAP was reduced significantly with postoperative CPAP use (preoperative AHI versus postoperative AHI, 37 ± 19 vs 12 ± 16 events per hour; mean difference, 27.52; 95% CI, 22.09–32.96; P < 0.001). Only Liao et al.20 compared perioperative AHI between CPAP versus no-CPAP group.
Five of 6 studies reported LOS.20,22,40–42 Four studies were used in the meta-analysis because they provided information on LOS by reporting mean ± SD20,41 or median (range), which could be converted to mean ± SD.42,43 The study by O’Gorman et al.22 was excluded from the analysis because LOS was provided in median (interquartile range). In the case-series study by Rennotte et al.,40 1 patient died on the 14th postoperative day, and 1 experienced postoperative adverse events with LOS of 35 days. Both these patients were in the no-CPAP group. Overall, in these 4 studies, the LOS showed a trend toward significance for the CPAP group (n = 278) versus no-CPAP group (n = 300) (4.0 ± 4.0 vs 4.4 ± 8.2 days, mean difference, −0.79; 95% CI, −1.59 to 0.01; asymptotic P = 0.05) (Fig. 5).
This systematic review/meta-analysis is the first to examine the effectiveness of CPAP therapy on postoperative adverse events, postoperative AHI, and LOS in OSA patients undergoing surgery. There was no significant difference in postoperative adverse events between CPAP (events = 134) and no-CPAP groups (event = 133) (P = 0.19). Patients with OSA who used CPAP either preoperatively and/or postoperatively compared with no-CPAP had a risk ratio of 0.88 (0.73–1.06) and 12% risk reduction of postoperative adverse events with a corresponding NNTB of 45.
The preoperative baseline AHI without CPAP was reduced significantly with postoperative CPAP use (preoperative AHI versus postoperative AHI, 37 ± 19 vs 12 ± 16 events per hour, P < 0.001). LOS showed a trend toward significance for the CPAP group versus no-CPAP group (4.0 ± 4.0 vs 4.4 ± 8.2 days; P = 0.05).
Despite advancement in anesthesia and surgical care, adverse postoperative events remain a significant problem in OSA patients undergoing surgery. OSA has been associated with an increased risk of postoperative oxygen desaturation, respiratory failure, atrial fibrillation, cardiac events, ICU transfers, and longer hospital stay.11–15 Furthermore, the risk may increase with undiagnosed and untreated OSA patients. Sedatives, narcotics, and anesthetics have been shown to increase pharyngeal collapse, decrease ventilatory response, and impair the arousal response, leading to worsening of sleep-disordered breathing in the perioperative period and postoperative complications. CPAP remains the most effective therapy for OSA, acting as a pneumatic splint to maintain upper airway patency as well as improving lung volumes and reducing atelectasis, thereby significantly reducing apneas and hypopneas and the associated hypoxemic and hypercapnic events. CPAP therapy can also decrease upper airway edema and inflammation leading to increased upper airway volume and stability. The application of CPAP also improves gas exchange, minimizes atelectasis formation, and increases functional residual capacity and oxygenation with reduction in the work of breathing.
CPAP has been shown to alleviate the symptoms of OSA, including amelioration of excessive daytime sleepiness, restoration of quality of life, improvement in vigilance, concentration and memory, lessening of fatigue, reduction of health care resource usage, and a decrease in traffic accidents.17,44–47 One study has shown reduced daytime sleepiness and decreased usage of medications for associated medical diseases by identifying patients having OSA in the preoperative clinic and providing long-term CPAP treatment.21 Moreover, long-term CPAP use has been associated with reduction in cardiovascular morbidity and mortality in both men and women with severe OSA.48,49 CPAP in sleep apnea patients improves existing comorbidities, including hypertension,50 cardiac function,51 diabetes mellitus,52 and other physiologic functions.53 It is possible that CPAP may improve preoperative optimization of such comorbidities. As perioperative physicians, anesthesiologists are positioned uniquely to diagnose and treat OSA, thereby providing an opportunity to improve the long-term health outcomes, including better sleep quality and less daytime sleepiness.21
The efficacy of CPAP in patients without a diagnosis of OSA has been well established for abdominal and cardiac surgery in the postoperative setting. Squadrone et al.26 demonstrated that the use of CPAP led to a reduction in the incidence of endotracheal intubation, pneumonia, infection, and sepsis in patients who develop hypoxemia after elective major abdominal surgery. Zarbock et al.30 also noted significant reduction in the rate of pulmonary complications with the prophylactic use of nasal CPAP in patients undergoing elective cardiac surgery. Kindgen-Milles et al.28 found that CPAP significantly reduced pulmonary morbidity and LOS after thoracoabdominal aortic surgery. A meta-analysis of 9 RCTs in patients undergoing abdominal surgery reported a reduction in the rate of postoperative pulmonary complications with the perioperative use of CPAP.27
The efficacy of CPAP in OSA patients undergoing surgery recently was demonstrated by Mutter et al.54 This cohort study demonstrated that CPAP significantly decreased the risk of cardiovascular complications, primarily cardiac arrest and shock. The cardiovascular complications were significantly different between undiagnosed OSA (odds ratio, 2.20 [95% CI, 1.16–4.17]) and diagnosed OSA patients (odds ratio, 0.75 [95% CI, 0.43–1.28]). Patients with a preoperative diagnosis of OSA and prescription for CPAP were less than half as likely to experience cardiovascular complications as those diagnosed after surgery.
At present, the efficacy of CPAP on the risk of perioperative cardiorespiratory events, AHI, and LOS in OSA patients is not known. The effectiveness of CPAP in 16 OSA patients was first reported in a case series by Rennotte et al.40 Two OSA patients without CPAP experienced postoperative adverse events and 1 patient died, whereas 14 patients treated with CPAP had an uneventful postoperative course. Gupta et al.41 identified that OSA patients without CPAP had greater postoperative adverse events compared with OSA patients treated with CPAP (44% vs 27%). Liao et al.39 reported that many of the OSA patients not using home CPAP developed an adverse event such as hypoxemia or upper airway obstruction resulting in initiation of postoperative CPAP. One recent RCT has shown the feasibility of perioperative APAP in OSA patients.20
Perioperative APAP significantly reduced postoperative AHI and improved oxygen saturation in patients with moderate and severe OSA. Perhaps perioperative reduction in AHI may lead to a decrease in postoperative adverse events. Even though CPAP is supposed to be effective in reducing hypoxemic episodes, we were unable to demonstrate a significant difference in postoperative adverse events between the CPAP and no-CPAP groups in our meta-analysis. Normally, it is difficult to demonstrate any intervention in its ability to impact significant cardiovascular events. Also, this might have been attributable to the large differences between studies in the event rates where the authors of the various studies did not examine the same events or had different criteria. Undoubtedly, larger studies will be needed to effectively address this question.
The benefits of CPAP may be less than expected in our meta-analysis because of the low compliance in the preoperative and postoperative period. Guralnick et al.55 found that surgical patients with suspected OSA had low compliance with anesthesiologists’ requests to undergo sleep studies, and those who were diagnosed with OSA and received APAP therapy showed suboptimal compliance (only 33% of patients used the CPAP >4 hours). Liao et al.20 also found that the perioperative compliance rate of CPAP was only 45%. In this review, we found that 428 patients used home CPAP, but only 211 patients (approximately 50%) continued CPAP postoperatively in the hospital.
The possible reasons for the low CPAP compliance in the postoperative period are postoperative discomfort and nausea/vomiting accounting for 70% of CPAP noncompliance.20 With better control of postoperative pain and nausea/vomiting, it may improve the compliance with CPAP among OSA patients. Also, health care professionals and patients might not have recognized the interaction of postoperative respiration depression by opioids and sleep-disordered breathing and the importance of continuation of postoperative CPAP. In addition, OSA patients who were noncompliant with their home CPAP might not have benefitted from the treatment, thus decreasing the effectiveness of CPAP. Therefore, it is plausible that improved CPAP compliance may further decrease postoperative adverse events, thus favoring the use of CPAP in OSA surgical patients. Further work needs to be performed in this area to streamline the process of perioperative treatment. Education of health care professionals and patients regarding the importance of perioperative CPAP is imperative to prevent postoperative adverse events during this vulnerable period that may be attributable to untreated OSA. Also, the severity of OSA may have an impact on the incidence of adverse postoperative events. It is possible that OSA patients not receiving home CPAP therapy might have had milder forms of OSA. These patients with mild OSA may have lower risks of adverse events versus patients with moderate-to-severe OSA, thus favoring the analysis toward OSA patients without CPAP.
Only 2 studies reported on the effect of CPAP on perioperative AHI.20,40 These patients used CPAP before surgery and continued in the postoperative period. In this review, we found that preoperative AHI was reduced significantly by an average of 25 events per hour postoperatively. Many clinicians may expect that CPAP (or APAP) may completely resolve sleep-disordered breathing. Our data summarizing the only 2 studies demonstrate that in fact some residual sleep-disordered breathing persists with mean AHI 12 ± 16 events per hour despite using CPAP.
The hospital LOS was 0.4 days shorter in the CPAP group compared with the no-CPAP group. Gupta et al.41 showed a prolonged LOS in the no-CPAP group compared with CPAP group (no-CPAP versus CPAP: 7.2 ± 3.1 vs 6.0 ± 2.1 days, P < 0.03). In contrast, O’Gorman et al.22 reported that APAP was not effective in shortening the LOS when applied postoperatively to patients deemed as high risk of having OSA. Because of its small sample size, however, this study was not statistically powered to demonstrate an effect on LOS with treatment.22 In another study in ambulatory surgical patients, CPAP was not effective for decreasing the median hospital LOS in OSA patients compared with non-OSA patients (7 vs 6 hours, P = 0.058).56 These contrasting results from different studies might have been attributable to varying criteria for hospital discharge from different institutions, changing practice standards over time, and possible cohort bias.
The literature currently lacks an adequate number of published RCTs to provide quality information regarding the use of preoperative and/or postoperative CPAP in OSA patients. Our literature search was limited to the English language, and we may have missed articles in other languages. Our strict inclusion criteria did not allow 6 studies with positive results to be included in the systematic review and meta-analysis, even though their results were in favor of CPAP in OSA patients. Most of these studies had missing data in either the study group or control group,32–34,36–38 which precluded them from being included in our meta-analysis.
Preexisting medical conditions may contribute to the development of postoperative adverse events and may influence the results. In our analysis, one of the studies did not specify the comorbid conditions.42 One limitation of the included studies is the lack of uniformity while reporting postoperative adverse events. Jensen et al.42 reported on anastomotic leaks, pulmonary complications, LOS, and death, whereas other studies reported on hypoxemia and ICU admissions. The trials also differed in how CPAP was applied, including the type of interfaces, devices, and the duration of use. With advances in anesthesia and surgery, postoperative cardiopulmonary adverse events are rare. The small number of patients in this meta-analysis who developed serious cardiopulmonary events is a limitation. Also, for LOS data, some patients in the study by Gupta et al. were receiving home CPAP, and we may not have seen the true effect of preoperative and/or postoperative CPAP. In the study by Rennotte et al., the LOS showed wide CIs as well.
The impact of reduction in AHI, shortened LOS, and the efficacy of CPAP in postoperative adverse events needs further investigation. It is difficult to conduct RCTs with a placebo arm in which patients with known OSA receiving home CPAP therapy are randomized to placebo perioperatively, which effectively deprives them from their standard home CPAP therapy for OSA. From a pragmatic standpoint, an RCT would be more feasible, although still challenging, in patients who are newly diagnosed with OSA and are waiting for their treatment. In fact, O’Gorman et al.22 had to discontinue their RCT after enrolling 86 patients labeled as high suspicion for OSA based on a screening questionnaire because of increased physician and patient awareness of postoperative complications associated with OSA and an unwillingness for patients identified at high risk for OSA to be randomized to standard care. Their sample size calculation was originally estimated at 208 patients. This might be the reason for the limited number of RCTs in the literature, because long-term CPAP use has been associated with a reduction in cardiovascular morbidity and mortality in both men and women with severe OSA.48,49 We may expect more observational studies on this topic. It is therefore important to have a summary of the existing data from systematic reviews and meta-analyses of the literature.
Moreover, we believe that it is important not to overinterpret our results. Given the improvement in surgical and anesthesia techniques, devastating postoperative outcomes have become relatively rare events. As such, it will be difficult to design an adequately powered RCT to assess the effectiveness of preoperative and/or postoperative CPAP on devastating cardiopulmonary outcomes. Our data also show that postoperative CPAP compliance is 50%. Despite the poor compliance, we found a 12% risk reduction in the CPAP group. It is plausible that larger studies with improved preoperative and postoperative CPAP compliance may further decrease postoperative adverse events, thus favoring CPAP use in OSA surgical patients. Nevertheless, the recent findings that diagnosed OSA patients with a CPAP prescription have fewer cardiac complications is important and may have implications for the optimal perioperative care of these patients.54
Importantly, this review summarizes the existing limited literature, and our hope is that it fosters further clinical research in this field by anesthesiologists and sleep medicine specialists. CPAP is an important intervention that is likely underused by anesthesiologists in the perioperative period. Further research also is needed to rigorously examine the possible beneficial impact of CPAP on the airway, lungs, circulatory, and nervous system. The only 2 RCTs were not designed to address the various potential perioperative benefits of CPAP. Further research is needed to address this important aspect of perioperative CPAP use in patients with OSA.
This paper serves several purposes: raising the awareness of preoperative and postoperative use of CPAP, educating the health professional about the findings in the literature, and serving as an impetus for further research in several areas.
We hope this review and meta-analysis will stimulate the readership and provide a focused assessment of the current limited state of knowledge so that future investigators and clinicians can formulate clinically relevant questions such as: (1) Which OSA phenotype undergoing which type of surgery would benefit the most from preoperative/postoperative CPAP treatment? (2) What is the optimal time and duration of CPAP therapy in the preoperative period? (3) What is the possible beneficial impact of CPAP on the airway, lungs, circulatory, and nervous system? (4) What are the best types of CPAP devices for perioperative use? (5) What are the reasons for the lack of compliance with CPAP and to determine how to improve perioperative CPAP compliance (6) What is the cost-effectiveness of preoperative diagnosis of OSA and perioperative implementation of CPAP therapy?
In conclusion, this systematic review suggests that CPAP therapy significantly reduces postoperative AHI and there was a trend toward shorter LOS in OSA patients. There was no significant difference in adverse events between the CPAP versus no-CPAP group. Further research is needed in the area of preoperative and postoperative CPAP use.
Name: Mahesh Nagappa, MD, DNB, MNAMS.
Contribution: This author helped conduct the study, analyze the data, and write the manuscript.
Attestation: Mahesh Nagappa approved the final manuscript.
Name: Babak Mokhlesi, MD, MSc.
Contribution: This author helped conduct the study, analyze the data, and write the manuscript.
Attestation: Babak Mokhlesi approved the final manuscript.
Name: Jean Wong, MD, FRCPC.
Contribution: This author helped analyze the data and write the manuscript.
Attestation: Jean Wong approved the final manuscript.
Name: David T. Wong, MD.
Contribution: This author helped analyze the data and write the manuscript.
Attestation: David T. Wong approved the final manuscript.
Name: Roop Kaw, MD.
Contribution: This author helped analyze the data and write the manuscript.
Attestation: Roop Kaw approved the final manuscript.
Name: Frances Chung, MD, FRCPC.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Frances Chung approved the final manuscript.
This manuscript was handled by: Peter S. A. Glass, MBChB.
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© 2015 International Anesthesia Research Society
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