Abstract: We included two trials involving 269 participants. The participants were mostly men (67%); the mean age was 65 years. The trials were conducted in China and Italy (one was a multicentre trial). Both trials included adults with acute respiratory failure after upper abdominal surgery. We judged both trials at high risk of bias. Compared to oxygen therapy, CPAP or bilevel NPPV may reduce the rate of tracheal intubation (risk ratio (RR) 0.25; 95% confidence interval (CI) 0.08 to 0.83; low quality evidence) with a number needed to treat for an additional beneficial outcome of 11. There was very low quality evidence that the intervention may also reduce ICU length of stay (mean difference (MD) -1.84 days; 95% CI -3.53 to -0.15). We found no differences for mortality (low quality evidence) and hospital length of stay. There was insufficient evidence to be certain that CPAP or NPPV had an effect on anastomotic leakage, pneumonia-related complications, and sepsis or infections. Findings from one trial of 60 participants suggested that bilevel NPPV, compared to oxygen therapy, may improve blood gas levels and blood pH one hour after the intervention (partial pressure of arterial oxygen (PaO2): MD 22.5 mm Hg; 95% CI 17.19 to 27.81; pH: MD 0.06; 95% CI 0.01 to 0.11; partial pressure of arterial carbon dioxide (PCO2) levels (MD -9.8 mm Hg; 95% CI -14.07 to -5.53). The trials included in this systematic review did not present data on the following outcomes that we intended to assess: gastric insufflation, fistulae, pneumothorax, bleeding, skin breakdown, eye irritation, sinus congestion, oronasal drying, and patient-ventilator asynchrony. The findings of this review indicate that CPAP or bilevel NPPV is an effective and safe intervention for the treatment of adults with acute respiratory failure after upper abdominal surgery. However, based on the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology, the quality of the evidence was low or very low. More good quality studies are needed to confirm these findings.

Plain-language summary: We searched scientific databases for clinical trials looking at the treatment of adults with acute respiratory failure following abdominal surgery. The trials compared NPPV with usual care(oxygen therapy through a face mask). We included two trials involving 269 participants.The participants were mostly men (67%) and on average 65 years of age. One trial was conducted in several intensive care units (ICU). Both trials included adults with acute respiratory failure after upper abdominal surgery. The evidence is current to May 2015. This review examined mortality, rate of tracheal intubation, length of stay in the ICU, length of hospital stay, complications after NPPV, and changes in the levels of gases within the blood (arterial blood gases). Compared with oxygen therapy, NPPV decreased the rate of tracheal intubation. Out of every 1000 adults who developed acute respiratory failure after upper abdominal surgery, 181 adults treated with oxygen therapy would need to be intubated compared with 54 adults treated with NPPV. When compared to oxygen therapy, NPPV tended to reduce mortality. However, since the number of participants included in the two trials was small, more studies are needed. The use of NPPV also reduced the length of stay in the ICU by almost two days when compared to oxygen therapy. However, the mean length of stay in the hospital was similar in the two groups. When compared to oxygen therapy, NPPV improved blood gas levels one hour after the intervention. There was insufficient evidence to be certain that CPAP or NPPV had an effect on anastomotic (e.g. where two pieces of intestine are joined together) leakage, pneumonia related complications and sepsis (blood poisoning) or infections. However, adults treated with NPPV had lower rates these complications than adults treated with oxygen. There was low quality evidence for hospital mortality, low quality of evidence for rate of tracheal intubation, and very low quality of evidence for ICU length of stay. The findings of this review showed that NPPV is an effective and safe treatment for adults with acute respiratory failure after upper abdominal surgery. However, due to the low quality of the evidence, more good quality studies are needed to confirm these findings.