Review question
Does continuous positive airway pressure during the postoperative period help reduce death and major lung complications after major abdominal surgery?
Background
General anaesthesia can lead to reduced lung volumes and collapse of the alveoli as well as to reversible, patchy collapse of areas of lung (atelectasis) and subsequent low oxygenation. These problems are worse in those patients undergoing upper abdominal surgery, in those who have predisposing factors such as obesity and chronic lung disease and in smokers. Continuous positive airway pressure (CPAP) is a type of therapy that uses a high-pressure gas source to deliver constant pressure to the airways throughout both inspiration and expiration in spontaneously breathing people; oxygen is added in appropriate amounts. CPAP uses a variety of masks, which are placed over the nose or mouth. The aim of this technique is to improve the oxygenation of patients while preventing common postoperative complications in vulnerable people, especially smokers and the obese.
This review was conducted to determine whether any difference can be found in death and major chest complications following major abdominal operations between patients treated with CPAP and those given standard care (oxygen by mask and physiotherapy).
Study characteristics
We searched the literature until 15 September 2013. We included all adults who underwent elective major abdominal surgery. We included only studies in which the intervention was started postoperatively.
We employed the standard methods of the Cochrane Anaesthesia Review Group for data collection and analysis. A total of 709 participants were included in the 10 selected trials. Considerable differences between studies were noted in the populations studied, duration of treatment and supportive care provided.
Key results
Two controlled trials (413 participants) reported deaths; no clear evidence showed a difference between CPAP and control groups. Six trials (249 participants) reported on atelectasis, which was reduced in the CPAP group. Pneumonia was reported in five trials (563 participants), and the rate of pneumonia was reduced in the CPAP group. The need for further respiratory support with artificial ventilation (reintubation) was reported in two studies, which favoured CPAP. No clear evidence revealed a difference between CPAP and control groups in rates of admission to intensive care units, nor were severely low oxygen levels reported.
Few studies reported on length of hospital stay and harm due to CPAP.
Quality of evidence
Substantial variability was seen in trial characteristics (heterogeneity), and risk of bias was high in six of the 10 studies. The included studies were small, and some were at least 20 years old; currently, computed tomography (CT) scans are used more often than chest x-rays and clinical examination alone for diagnosis. The summary of findings (GRADE) suggests that the strength of evidence supporting the use of CPAP was ‘very low.’ This means that recommendations based on currently available evidence from randomized controlled trials investigating use of CPAP during the postoperative period are not definitive.
Very low-quality evidence from this review suggests that CPAP initiated during the postoperative period might reduce postoperative atelectasis, pneumonia and reintubation, but its effects on mortality, hypoxia or invasive ventilation are uncertain. Evidence is not sufficiently strong to confirm the benefits or harms of CPAP during the postoperative period in those undergoing major abdominal surgery. Most of the included studies did not report on adverse effects attributed to CPAP.
New, high-quality research is much needed to evaluate the use of CPAP in preventing mortality and morbidity following major abdominal surgery. With increasing availability of CPAP to our surgical patients and its potential to improve outcomes (possibly in conjunction with intraoperative lung protective ventilation strategies), unanswered questions regarding its efficacy and safety need to be addressed. Any future study must report on the adverse effects of CPAP.
Major abdominal surgery can be associated with a number of serious complications that may impair patient recovery. In particular, postoperative pulmonary complications (PPCs), including respiratory complications such as atelectasis and pneumonia, are a major contributor to postoperative morbidity and may even contribute to increased mortality. Continuous positive airway pressure (CPAP) is a type of therapy that uses a high-pressure gas source to deliver constant positive pressure to the airways throughout both inspiration and expiration. This approach is expected to prevent some pulmonary complications, thus reducing mortality.
To determine whether any difference can be found in the rate of mortality and adverse events following major abdominal surgery in patients treated postoperatively with CPAP versus standard care, which may include traditional oxygen delivery systems, physiotherapy and incentive spirometry.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) 2013, Issue 9; Ovid MEDLINE (1966 to 15 September 2013); EMBASE (1988 to 15 September 2013); Web of Science (to September 2013) and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (to September 2013).
We included all randomized controlled trials (RCTs) in which CPAP was compared with standard care for prevention of postoperative mortality and adverse events following major abdominal surgery. We included all adults (adults as defined by individual studies) of both sexes. The intervention of CPAP was applied during the postoperative period. We excluded studies in which participants had received PEEP during surgery.
Two review authors independently selected studies that met the selection criteria from all studies identified by the search strategy. Two review authors extracted the data and assessed risk of bias separately, using a data extraction form. Data entry into RevMan was performed by one review author and was checked by another for accuracy. We performed a limited meta-analysis and constructed a summary of findings table.
We selected 10 studies for inclusion in the review from 5236 studies identified in the search. These 10 studies included a total of 709 participants. Risk of bias for the included studies was assessed as high in six studies and as unclear in four studies.
Two RCTs reported all-cause mortality. Among 413 participants, there was no clear evidence of a difference in mortality between CPAP and control groups, and considerable heterogeneity between trials was noted (risk ratio (RR) 1.28, 95% confidence interval (CI) 0.35 to 4.66; I2 = 75%).
Six studies reported demonstrable atelectasis in the study population. A reduction in atelectasis was observed in the CPAP group, although heterogeneity between studies was substantial (RR 0.62, 95% CI 0.45 to 0.86; I2 = 61%). Pneumonia was reported in five studies, including 563 participants; CPAP reduced the rate of pneumonia, and no important heterogeneity was noted (RR 0.43, 95% CI 0.21 to 0.84; I2 = 0%). The number of participants identified as having serious hypoxia was reported in two studies, with no clear difference between CPAP and control groups, given imprecise results and substantial heterogeneity between trials (RR 0.48, 95% CI 0.22 to 1.02; I2 = 67%). A reduced rate of reintubation was reported in the CPAP group compared with the control group in two studies, and no important heterogeneity was identified (RR 0.14, 95% CI 0.03 to 0.58; I2 = 0%). Admission into the intensive care unit (ICU) for invasive ventilation and supportive care was reduced in the CPAP group, but this finding did not reach statistical significance (RR 0.45, 95% CI 0.18 to 1.14; I2 = 0).
Secondary outcomes such as length of hospital stay and adverse effects were only minimally reported.
A summary of findings table was constructed using the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) principle. The quality of evidence was determined to be very low.