Meta-analysis: Ventilation Strategies and Outcomes of the Acute Respiratory Distress Syndrome and Acute Lung Injury

Background: Trials have provided conflicting results regarding the effect of different ventilatory strategies on the outcomes of patients with the acute respiratory distress syndrome (ARDS) and acute lung injury. Purpose: To determine whether ventilation with low tidal volume (VT) and limited airway pressure or higher positive end-expiratory pressure (PEEP) improves outcomes for patients with ARDS or acute lung injury. Data Sources: Multiple computerized databases (through March 2009), reference lists of identified articles, and queries of principal investigators. No language restrictions were applied. Study Selection: Randomized, controlled trials (RCTs) reporting mortality and comparing lower versus higher VT ventilation, lower versus higher PEEP, or a combination of both in adults with ARDS or acute lung injury. Data Extraction: Using a standard protocol, 2 reviewer teams assessed trial eligibility and abstracted data on quality of study design and conduct, population characteristics, intervention, co-interventions, and confounding variables. Data Synthesis: 4 RCTs tested lower versus higher VT ventilation at similar PEEP in 1149 patients, 3 RCTs compared lower versus higher PEEP at low VT ventilation in 2299 patients, and 2 RCTs compared a combination of higher VT and lower PEEP ventilation versus lower VT and higher PEEP ventilation in 148 patients. Lower VT ventilation reduced hospital mortality (odds ratio, 0.75 [95% CI, 0.58 to 0.96]; P = 0.02) compared with higher VT ventilation at similar PEEP. Higher PEEP did not reduce hospital mortality ( odds ratio, 0.86 [CI, 0.72 to 1.02]; P = 0.08) compared with lower PEEP using low VT ventilation. Higher PEEP reduced the need for rescue therapy to prevent life-threatening hypoxemia (odds ratio, 0.51 [CI, 0.36 to 0.71]; P < 0.001) and death (odds ratio, 0.51 [CI, 0.36 to 0.71]; P < 0.001) in patients receiving rescue therapies. Limitations: Pooling according to similar ventilatory strategies resulted in few RCTs analyzed in each group. The benefit of low VT is derived from only 1 study. Conclusion: Available evidence from a limited number of RCTs shows better outcomes with routine use of low VT but not high PEEP ventilation in unselected patients with ARDS or acute lung injury. High PEEP may help to prevent life-threatening hypoxemia in selected patients.