Abstract: We included 24 studies of critically ill adults. No study reported mortality as an outcome of interest. Two randomized controlled trials (RCTs) examined lateral positioning for pulmonary morbidity outcomes but provided insufficient information for meta-analysis. A total of 22 randomized trials examined effects of lateral positioning (four parallel-group and 18 cross-over designs) by measuring various continuous data outcomes commonly used to detect adverse cardiopulmonary events within critical care areas. However, parallel-group studies were not comparable, and cross-over studies provided limited data as the result of unit of analysis errors. Eight studies provided some data; most of these were single studies with small effects that were imprecise. We pooled partial pressure of arterial oxygen (PaO2) as a measure to detect hypoxaemia from two small studies of participants with unilateral lung disease (n = 19). The mean difference (MD) between lateral positions (bad lung down versus good lung down) was approximately 50 mmHg (MD -49.26 mmHg, 95% confidence interval (CI) -67.33 to -31.18; P value < 0.00001). Despite a lower mean PaO2 for bad lung down, hypoxaemia (mean PaO2 < 60 mmHg) was not consistently reported. Furthermore, pooled data had methodological shortcomings with unclear risk of bias. We had similar doubts regarding internal validity for other studies included in the review. Review authors could provide no clinical practice recommendations based on the findings of included studies. Available research could not eliminate the uncertainty surrounding benefits and/or risks associated with lateral positioning of critically ill adult patients. Research gaps include the effectiveness of lateral positioning compared with semi recumbent positioning for mechanically ventilated patients, lateral positioning compared with prone positioning for acute respiratory distress syndrome (ARDS) and less frequent changes in body position. We recommend that future research be undertaken to address whether the routine practice of repositioning patients on their side benefits all, some or few critically ill patients.

Plain-language summary: We included randomized studies of critically ill adults receiving treatment in intensive care units and in other critical care areas. We selected studies that included lateral positioning after a single turn or following repetitive turns. The duration of each body position was 10 minutes or longer. Comparisons included the other lateral position (opposite side), as well as supine (lying on your back), semi recumbent (lying on your back with your upper body elevated to a 45-degree angle) and prone (lying on your stomach) positions. Results We found 24 eligible studies. No studies reported on mortality. Two studies reported on pulmonary morbidity following cardiac surgery, but available data were insufficient for analysis. The other studies reported measures that we included to identify clinical adverse events. Most of these studies did not report results in a way that could be combined for review of evidence, and trial design was often dissimilar. We compared two studies of critically ill adults with unilateral lung disease (one 'bad lung' and one 'good lung'). Oxygen levels within the blood were lower for 'bad lung down' (side lying with the 'bad lung' lowermost). However, the sample was small, both studies were of poor quality and very low oxygen levels in the blood were not consistently found across studies. Therefore, results need to be viewed with caution. Conclusion We found no clear evidence on the effectiveness of routine lateral repositioning or the effects of a single turn for critically ill patients. Good quality studies are needed to find out whether routine lateral repositioning is still recommended for most critically ill patients, and whether one body position is best avoided for some.