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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

Prone positioning in hypoxemic respiratory failure: meta-analysis of randomized controlled trials

P Kopterides, II Siempos, and A Armaganidis.

Review published: 2009.

Link to full article: [Journal publisher]

CRD summary

The review found that prone positioning did not appear to affect overall mortality associated with hypoxaemic respiratory failure compared with supine positioning, although it may benefit the most severely-ill patients. The review was well conducted and the authors’ conclusions appear reliable.

Authors' objectives

To evaluate the effect of prone positioning on clinical outcomes in patients with hypoxaemic respiratory failure.


MEDLINE, Current Contents and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched from inception to January 2007 for studies in any language. Search terms were reported. Reference lists of relevant studies and reviews were also checked.

Study selection

Randomised controlled trials (RCTs) that compared prone with supine positioning in the management of adults with hypoxaemic respiratory failure were eligible for inclusion. Trials were required to report intensive care unit mortality (primary outcome), hospital mortality, clinical outcomes or complications of both positions. Outcomes were defined in detail in the review. Trials reporting only gas exchange, haemodynamics or respiratory mechanics were excluded.

Participants in the included trials were adults undergoing mechanical ventilation, most of whom had acute lung injury or acute respiratory distress syndrome. The mean Simplified Acute Physiology Score II varied across trial groups, ranging from 38 to 46.1 (where reported). The proportion of cases in which hypoxaemic respiratory failure was caused by pneumonia varied across trial groups, ranging from 14 to 62%. The time interval from diagnosis to initiation of prone positioning also differed across trials. The mean daily duration of prone positioning (where reported) ranged from seven to 17 hours (daily mean); the overall duration ranged from two days to at least 10 days. Trials differed as to whether participants receiving co-interventions (e.g. nitric oxide) were eligible.

Two reviewers independently selected the studies.

Assessment of study quality

Trials were allocated 1 point for specifying each of the following: randomisation, random sequence generation, allocation concealment, double blinding, and information on withdrawals or drop-outs (maximum 5 points). Trials were designated as high quality (more than 2 points) or low quality (2 points or fewer).

Two reviewers independently assessed study validity.

Data extraction

Odds ratios (ORs) were extracted or calculated for dichotomous outcomes and mean differences for continuous outcomes, with 95% confidence intervals (CIs). Data were analysed both by intention-to-treat and per protocol (including only clinically evaluable participants who had not crossed over from one study arm to the other).

Two reviewers independently extracted the data, resolving differences by consensus or by referral to a third reviewer.

Methods of synthesis

Trials were combined to calculate pooled odd ratios and 95% confidence intervals for dichotomous data, using the Mantel-Haenszel fixed-effect and DerSimonian and Laird random-effects models. For continuous data weighted mean differences (WMDs) and 95% confidence intervals were calculated. Heterogeneity was assessed using the χ2 and I2 tests. Fixed-effect models were presented, although it was planned to use random-effects if there was significant statistical heterogeneity. Publication bias was not formally assessed as there were too few trials. A post-hoc subgroup analysis investigated intensive care unit mortality in the most severely-ill group (as defined in the review).

Results of the review

Four RCTs were included (n=1,271 patients, range 40 to 791). Three were high quality trials (scoring 3 out of 5 points) and one low quality trial (scoring 2 points).

There was no statistically significant difference between the prone and supine position groups in overall intensive care unit (ICU) mortality (four RCTs). However among the most severely-ill patients, the prone position was associated with significantly lower ICU mortality (OR 0.34, 95% CI 0.18 to 0.66; two RCTs; n=195 patients).

There was no statistically significant difference between the prone and supine position groups in ventilator-associated pneumonia (three RCTs), ICU length of stay (one RCT), duration of mechanical ventilation (two RCTs) or pneumothorax (two RCTs).

In the prone positioning group, there was a significantly higher rate of new or worsening pressure sores (OR 1.49, 95% CI 1.17 to 1.89; three RCTs; n=1,135 patients).

There was no significant statistical heterogeneity for any analysis.

All results presented above were by intention-to-treat.

Authors' conclusions

Prone positioning did not appear to affect overall mortality among patients with hypoxaemic respiratory failure, although a benefit for the most severely-ill patients could not be excluded.

CRD commentary

The objectives and inclusion criteria of the review were clear and relevant sources were searched for studies in any language. It was unclear whether the search was limited by publication status, but there were insufficient studies to assess the potential for publication bias. Steps were taken to minimise the risk of reviewer bias and error by having more than one reviewer independently select studies, assess validity and extract the data.

Appropriate statistical techniques were used to combine the trials and assess for heterogeneity. The authors acknowledged the potential for bias in the review arising from the small amount of data and from differences between the trials; they were suitably cautious in interpreting their main findings.

The review was well conducted and the authors’ conclusions appear reliable.

Implications of the review for practice and research

Practice: The authors stated that explicit guidelines on the use of prone positioning would facilitate its implementation and decrease associated potential safety risks.

Research: The authors stated that a multi-centre study should be conducted among patients with severe hypoxaemic respiratory failure, with prone positioning started early for up to 20 hours per day, adequate treatment duration, well-defined outcomes, and protocols for ventilation and care practices. They noted that such a study was currently in progress.


Not stated.

Bibliographic details

Kopterides P, Siempos II, Armaganidis A. Prone positioning in hypoxemic respiratory failure: meta-analysis of randomized controlled trials. Journal of Critical Care 2009; 24(1): 89-100. [PubMed: 19272544]

Indexing Status

Subject indexing assigned by NLM


Adult; Anoxia /mortality /physiopathology /therapy; Critical Care /methods; Evidence-Based Practice; Hospital Mortality; Humans; Incidence; Length of Stay; Patient Selection; Pneumonia, Ventilator-Associated /epidemiology /etiology; Pneumothorax /epidemiology /etiology; Pressure Ulcer /epidemiology /etiology; Prone Position /physiology; Randomized Controlled Trials as Topic; Research Design; Respiration, Artificial /adverse effects /methods; Respiratory Distress Syndrome, Adult /mortality /therapy; Respiratory Insufficiency /mortality /physiopathology /therapy; Respiratory Mechanics; Safety; Supine Position /physiology; Tidal Volume; Treatment Outcome



Database entry date


Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 19272544


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