Abstract: We included 10 trials involving 878 participants, among which 28 participants in two trials did not provide complete data due to loss to follow-up. We judged all trials to be at high risk of bias. Semi-recumbent position (30º to 60º) versus supine position (0° to 10°) A semi-recumbent position (30º to 60º) significantly reduced the risk of clinically suspected VAP compared to a 0º to 10º supine position (eight trials, 759 participants, 14.3% versus 40.2%, RR 0.36; 95% CI 0.25 to 0.50; risk difference (RD) 25.7%; 95% CI 20.1% to 30.1%; GRADE: moderate quality evidence). There was no significant difference between the two positions in the following outcomes: microbiologically confirmed VAP (three trials, 419 participants, 12.6% versus 31.6%, RR 0.44; 95% CI 0.11 to 1.77; GRADE: very low quality evidence), ICU mortality (two trials, 307 participants, 29.8% versus 34.3%, RR 0.87; 95% CI 0.59 to 1.27; GRADE: low quality evidence), hospital mortality (three trials, 346 participants, 23.8% versus 27.6%, RR 0.84; 95% CI 0.59 to 1.20; GRADE: low quality evidence), length of ICU stay (three trials, 346 participants, MD -1.64 days; 95% CI -4.41 to 1.14 days; GRADE moderate quality evidence), length of hospital stay (two trials, 260 participants, MD -9.47 days; 95% CI -34.21 to 15.27 days; GRADE: very low quality evidence), duration of ventilation (four trials, 458 participants, MD -3.35 days; 95% CI -7.80 to 1.09 days), antibiotic use (three trials, 284 participants, 84.8% versus 84.2%, RR 1.00; 95% CI 0.97 to 1.03) and pressure ulcers (one trial, 221 participants, 28% versus 30%, RR 0.91; 95% CI 0.60 to 1.38; GRADE: low quality evidence). No other adverse events were reported. Semi-recumbent position (45°) versus 25° to 30° We found no statistically significant differences in the following prespecified outcomes: clinically suspected VAP (two trials, 91 participants, RR 0.74; 95% CI 0.35 to 1.56; GRADE: very low quality evidence), microbiologically confirmed VAP (one trial, 30 participants, RR 0.61; 95% CI 0.20 to 1.84: GRADE: very low quality evidence), ICU mortality (one trial, 30 participants, RR 0.57; 95% CI 0.15 to 2.13; GRADE: very low quality evidence), hospital mortality (two trials, 91 participants, RR 1.00; 95% CI 0.38 to 2.65; GRADE: very low quality evidence), length of ICU stay (one trial, 30 participants, MD 1.6 days; 95% CI -0.88 to 4.08 days; GRADE: very low quality evidence) and antibiotic use (two trials, 91 participants, RR 1.11; 95% CI 0.84 to 1.47). No adverse events were reported. A semi-recumbent position (≧ 30º) may reduce clinically suspected VAP compared to a 0° to 10° supine position. However, the evidence is seriously limited with a high risk of bias. No adequate evidence is available to draw any definitive conclusion on other outcomes and the comparison of alternative semi-recumbent positions. Adverse events, particularly venous thromboembolism, were under-reported.

Plain-language summary: We identified 10 studies involving 878 participants. Twenty-eight participants were lost to follow-up. The evidence is current up to 27 October 2015. All participants were recruited from intensive care units (ICUs) and received mechanical ventilation for more than 48 hours. Moderate quality evidence from eight studies involving 759 participants demonstrated that a semi-recumbent (30º to 60º) position reduced clinically suspected VAP by 25.7% when compared to a 0° to 10° supine position. Based on this result, we would expect that out of 1000 critically ill adult patients who are nursed in the semi-recumbent position (30º to 60º) for more than 48 hours, 145 patients would experience clinically suspected VAP compared to 402 patients nursed in the 0° to 10° supine position. There was no significant difference between the two positions in reducing microbiologically confirmed VAP (very low quality evidence), mortality (low quality evidence), length of ICU stay (moderate quality evidence), hospital stay (very low quality evidence), duration of ventilation or use of antibiotics. The main limitations of the evidence were the small numbers of participants contributing data to the analyses and that for some studies researchers would have known which treatment group participants were from (a risk of bias). Only two studies with 91 participants compared different degrees of bed head angle (45° versus 25° to 30° semi-recumbent position). Very low quality evidence showed no statistically significant differences in the effects of VAP (clinically suspected and microbiologically confirmed), mortality (ICU and hospital), length of ICU stay or use of antibiotics. Only one study reported the adverse event of pressure ulcers and did not find a difference between the 45° semi-recumbent and 10° supine positions. No other adverse events, such as thromboembolism, or side effects on heart rate or blood pressure were reported. The balance of the benefit and harm of semi-recumbent positioning still remains uncertain due to the limited numbers of studies and the low quality of the existing evidence. More high quality evidence is required on the effects of the semi-recumbent versus supine position and the optimal body positions.