Prone (face-down) position for mechanical ventilation of adults with acute respiratory failure

Review question

This review sought to investigate whether face-down ventilation could improve important outcomes by, for instance, reducing the death rate (mortality) among individuals requiring mechanical ventilation in intensive care. We also wanted to identify disadvantages and complications associated with prone positioning, as well as long-term benefits.

Background

People who are admitted to an intensive care unit and need assistance with breathing provided by a ventilator (mechanical ventilation) because of lung damage caused by illness have a high risk of dying. Lungs that are affected by conditions such as pneumonia will consist of normal and abnormal or diseased areas. Recovery of diseased areas takes time, and a person may need support with ventilation while this occurs. Ventilation support is potentially lifesaving, as it maintains proper oxygen levels in the blood while removing carbon dioxide waste. However, the ventilator itself can cause inflammation and thus additional lung complications. The harder a ventilator has to work to achieve normal oxygenation and removal of carbon dioxide, the more likely it is that healthy, normal areas of the lung may be damaged, and the person's condition made worse. Ventilation with the person lying face-down (prone) instead of face-up (supine) might improve how well the ventilator works, thereby reducing these undesirable side effects.

Study characteristics

We identified and included in this review randomized controlled trials of adults that compared conventional mechanical ventilation in the face-down versus the face-up position.

Key results

Reports from nine trials of 2165 participants (10 publications) show that prone ventilation did not appear to be of benefit for all participants requiring ventilation but identified some situations in which it may improve survival. One group of participants with the most severe lung damage appeared to have reduced mortality, as did participants who received treatment early and for prolonged periods. Complications were described. The most common of these were pressure sores and tracheal tube blockage or obstruction. Low blood pressure and abnormal heart rhythms were also seen. Clinicians need to be aware of these and to take preventative actions when possible. The application of prone position to all participants in intensive care who have low oxygen levels is not warranted, but some particular groups of participants, for example, those with especially low oxygen levels, would benefit from prone positioning. Further clinical trials would assist in clarifying potential benefits for such patient groups but further trials may not take place because of the very large treatment benefit observed in the most recent clinical trial of participants with very low oxygen levels. In the absence of new trials, meta-analysis of individual patient data may facilitate further assessment.

Quality of the evidence

The quality of the evidence for primary outcomes of this systematic review was low as a result of serious inconsistency and important potential bias.

The evidence is current to 31 January 2014. We reran searches in CENTRAL, MEDLINE, EMBASE, CINAHL and LILACS in June 2015. Five new studies of potential interest were added to the list of "Studies awaiting classification" and will be incorporated into formal review findings during the review update.

Authors' conclusions: 

We found no convincing evidence of benefit nor harm from universal application of PP in adults with hypoxaemia mechanically ventilated in intensive care units (ICUs). Three subgroups (early implementation of PP, prolonged adoption of PP and severe hypoxaemia at study entry) suggested that prone positioning may confer a statistically significant mortality advantage. Additional adequately powered studies would be required to confirm or refute these possibilities of subgroup benefit but are unlikely, given results of the most recent study and recommendations derived from several published subgroup analyses. Meta-analysis of individual patient data could be useful for further data exploration in this regard. Complications such as tracheal obstruction are increased with use of prone ventilation. Long-term mortality data (12 months and beyond), as well as functional, neuro-psychological and quality of life data, are required if future studies are to better inform the role of PP in the management of hypoxaemic respiratory failure in the ICU.

Read the full abstract...
Background: 

Acute hypoxaemia de novo or on a background of chronic hypoxaemia is a common reason for admission to intensive care and for provision of mechanical ventilation. Various refinements of mechanical ventilation or adjuncts are employed to improve patient outcomes. Mortality from acute respiratory distress syndrome, one of the main contributors to the need for mechanical ventilation for hypoxaemia, remains approximately 40%. Ventilation in the prone position may improve lung mechanics and gas exchange and could improve outcomes.

Objectives: 

The objectives of this review are (1) to ascertain whether prone ventilation offers a mortality advantage when compared with traditional supine or semi recumbent ventilation in patients with severe acute respiratory failure requiring conventional invasive artificial ventilation, and (2) to supplement previous systematic reviews on prone ventilation for hypoxaemic respiratory failure in an adult population.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 1), Ovid MEDLINE (1950 to 31 January 2014), EMBASE (1980 to 31 January 2014), the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to 31 January 2014) and Latin American Caribbean Health Sciences Literature (LILACS) (1992 to 31 January 2014) in Ovid MEDLINE for eligible randomized controlled trials. We also searched for studies by handsearching reference lists of relevant articles, by contacting colleagues and by handsearching published proceedings of relevant journals. We applied no language constraints, and we reran the searches in CENTRAL, MEDLINE, EMBASE, CINAHL and LILACS in June 2015. We added five new studies of potential interest to the list of "Studies awaiting classification" and will incorporate them into formal review findings during the review update.

Selection criteria: 

We included randomized controlled trials (RCTs) that examined the effects of prone position versus supine/semi recumbent position during conventional mechanical ventilation in adult participants with acute hypoxaemia.

Data collection and analysis: 

Two review authors independently reviewed all trials identified by the search and assessed them for suitability, methods and quality. Two review authors extracted data, and three review authors reviewed the data extracted. We analysed data using Review Manager software and pooled included studies to determine the risk ratio (RR) for mortality and the risk ratio or mean difference (MD) for secondary outcomes; we also performed subgroup analyses and sensitivity analyses.

Main results: 

We identified nine relevant RCTs, which enrolled a total of 2165 participants (10 publications). All recruited participants suffered from disorders of lung function causing moderate to severe hypoxaemia and requiring mechanical ventilation, so they were fairly comparable, given the heterogeneity of specific disease diagnoses in intensive care. Risk of bias, although acceptable in the view of the review authors, was inevitable: Blinding of participants and carers to treatment allocation was not possible (face-up vs face-down).

Primary analyses of short- and longer-term mortality pooled from six trials demonstrated an RR of 0.84 to 0.86 in favour of the prone position (PP), but findings were not statistically significant: In the short term, mortality for those ventilated prone was 33.4% (363/1086) and supine 38.3% (395/1031). This resulted in an RR of 0.84 (95% confidence interval (CI) 0.69 to 1.02) marginally in favour of PP. For longer-term mortality, results showed 41.7% (462/1107) for prone and 47.1% (490/1041) for supine positions, with an RR of 0.86 (95% CI 0.72 to 1.03). The quality of the evidence for both outcomes was rated as low as a result of important potential bias and serious inconsistency.

Subgroup analyses for mortality identified three groups consistently favouring PP: those recruited within 48 hours of meeting entry criteria (five trials; 1024 participants showed an RR of 0.75 (95% CI 0.59 to 94)); those treated in the PP for 16 or more hours per day (five trials; 1005 participants showed an RR of 0.77 (95% CI 0.61 to 0.99)); and participants with more severe hypoxaemia at trial entry (six trials; 1108 participants showed an RR of 0.77 (95% CI 0.65 to 0.92)). The quality of the evidence for these outcomes was rated as moderate as a result of potentially important bias.

Prone positioning appeared to influence adverse effects: Pressure sores (three trials; 366 participants) with an RR of 1.37 (95% CI 1.05 to 1.79) and tracheal tube obstruction with an RR of 1.78 (95% CI 1.22 to 2.60) were increased with prone ventilation. Reporting of arrhythmias was reduced with PP, with an RR of 0.64 (95% CI 0.47 to 0.87).

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