In two meta-analyses and one previous observational study, prone positioning was associated with improved survival for patients with severely hypoxemic acute respiratory distress syndrome (ARDS). However, the findings in these studies were in contradistinction to previously conducted randomized trials. To further evaluate the effectiveness of early prone positioning in severe ARDS, Guerin and colleagues from the PROSEVA Study Group designed a randomized controlled trial comparing early application of prone positioning versus supine positioning for patients with severe ARDS. Results were published in a recent issue of The New England Journal of Medicine.
The pre-Berlin definition of ARDS was used to screen 3,449 patients from 26 intensive care units (ICU) in France and one in Spain. After a stabilization period of 12 to 24 hours, patients were randomly assigned to a prone or supine positioning study group. Patients in the prone group were placed in a prone position for at least 16 consecutive hours every day for up to 28 days. Outcomes assessors were blinded to group assignments. The primary outcome of interest was mortality at day 28. Secondary end points were rate of extubation, ICU length of stay, complications, and several other outcomes. Data were analyzed according to the intention-to-treat principle; patient survival was assessed with the Kaplan-Meier method and Cox proportional-hazards regression.
There were 229 patients assigned to the supine group and 237 assigned to the prone group. Patients were similar within the two groups with the exception of a higher Sequential Organ Failure Assessment (SOFA) score and more vasopressor use in the supine group, as well as more neuromuscular blocker use in the prone group. Mortality at day 28 was significantly lower in the prone group (16%) compared to the supine group (32.8%; p<0.001). After adjustment for the SOFA score, patients in the prone group had a lower hazard of death compared to the supine group (hazard ratio = 0.42; 95% confidence interval [CI], 0.26-0.66; p<0.001). Patients in the prone group also had improved 90-day survival and more ventilator-free days compared to the supine group. No significant differences were detected between the groups in terms of complications.
The positive findings found in this study may be different from those of previous negative randomized trials for several reasons. Patients in this study had longer prone-positioning sessions administered over several days. Tidal volumes and plateau pressures were more rigorously controlled than in previous trials. Patients were also recruited into the study only after a period of 12 hours during which ARDS criteria were clearly confirmed. The external generalizability of this work may be limited in centers where technical and logistical expertise for prone positioning is limited; the low rate of complications in this study may not be observed in such centers.
Concise Critical Appraisal is a regular feature authored by SCCM member Samuel M. Galvagno Jr., DO, PhD. Each installment highlights journal articles most relevant to the critical care practitioner.