Eight RCTs (n=431) were included in the review. Median sample size was 41 (range 16 to 148). Six trials were considered to be of high methodological quality. Risk of bias was unclear in the remaining two trials. All trials used concealed allocation and reported data permitting intention-to-treat analysis. Withdrawals and losses to follow-up were minimal.
High frequency oscillation significantly reduced mortality at discharge or 30 days (RR 0.77, 95% CI 0.61 to 0.98; six RCTs). There was no evidence of statistically significant heterogeneity (I2=0%). There were no statistically significant differences in treatment effect in the subgroup analyses, including that of tidal volume in control groups. There was no evidence of publication bias.
There was a statistically significantly reduced rate of treatment failure (refractory hypoxaemia, hypercapnia, hypotension or barotrauma) in groups treated with high frequency oscillation (RR 0.67, 95% CI 0.46, 0.99; five RCTs) without significant heterogeneity (I2=0%). There were no other statistically significant differences between treatment groups, including adverse events.
Analyses of physiological outcomes were also reported: increases in PaO2/FiO2 ratio of 16% to 24% relative to conventional mechanical ventilation and increased mean airway pressure by 22% to 33% at 24, 48, and 72 hours, but no effects on the oxygenation index and PaCO2.