Feasibility and effectiveness of prone position in morbidly obese ARDS patients: a case-control clinical study

Introduction

Obese patients are at risk of developing atelectasis and acute respiratory distress syndrome (ARDS) [1]. The prone position (PP) may reduce atelectasis, and improves oxygenation and outcome in severe hypoxemic patients in ARDS [2], but little is known about its effect in obese ARDS patients.

Methods

Morbidly obese patients (body mass index (BMI) ≥35 kg/m²) in PP with ARDS (PaO₂/FiO₂ ratio ≤200 mmHg) were matched to nonobese (BMI <30 kg/m²) ARDS patients in a case-control clinical study. The primary endpoints were safety and complications of PP; the second endpoints were the effect on oxygenation (PaO₂/FiO₂ ratio at the end of PP), length of mechanical ventilation and ICU stay, nosocomial infections and mortality.

Results

Between January 2005 and December 2009, 149 patients were admitted for ARDS. Thirty-three obese patients were matched with 33 nonobese patients. Median PP duration was 9 (6 to 11) hours in obese patients and 8 (7 to 12) hours in nonobese patients (P = 0.28). We collected 51 complications, of which 25 in obese patients and 26 in nonobese patients. The number of patients with at least one complication was similar across groups (n = 10, 30%). The PaO₂/FiO₂ ratio (Figure 1) increased significantly more in obese patients (from 118 ± 43 to 222 ± 84 mmHg) than in nonobese patients (from 113 ± 43 mmHg to 174 ± 80 mmHg, P = 0.03). Length of mechanical ventilation, ICU stay and nosocomial infections did not differ significantly, but mortality at 90 days was significantly lower in obese patients (27 vs. 48%, P < 0.05).

Figure 1

Individual variations of PaO ₂ /FiO ₂ ratio between supine and prone positions in obese and nonobese patients.

Conclusion

PP seems safe in obese patients and may improve oxygenation more than in nonobese patients. Obese patients could be a subgroup of ARDS patients who may benefit most from PP.