The importance of prone position ventilation in ARDS for the improvement of oxygenation index

Introduction

In acute respiratory distress syndrome (ARDS) change from supine (SP) to prone position can improve gas exchange by recruiting alveoli situated in dorsal dependent regions and by alteration of ventilation/perfusion ratio. The aim of this study was to investigate the effect of prone position (PP) after application of high fractional inspired oxygen (hFiO₂), inverse ratio ventilation (IRV), positive end exspiratory pressure (PEEP)as well as kinetic therapy (KT) and hemofiltration (HF) did not lead to a breakthrough in treatment of severe ARDS.

Methods

We studied 22 consecutive patients with severe ARDS (mean age 64 ± 11.16 [SE] years) in a clinical follow-up design. All patients received hFiO₂ IRV and PEEP before starting prone position, while 15 obtained HF (Prisma^® Hospal) and 3 KT (Rotorest^®). Prone position was commenced 82 h median time (range 6 to 417 h) after onset of severe ARDS at a mean PaO₂/FiO₂ ratio of 98.02 ± 6.11 (SEM) mmHg. We compared individual oxygenation index (PaO₂/FiO₂) before and after start of prone position with linear regression analysis (Excel^® regression-procedure; SPSS^® T-test).

Results

In the stage of supine position neither treatment with hFiO₂, IRV, PEEP nor HF and KT led to an improvement of oxygenation index. After starting prone position ventilation 20 of 22 patients showed a significant increase of the oxygenation index (responder: Y_[SP]= [-46.11 ± 3.41] × X + [194.03 ± 3.78]:

Y_[PP] = [25.00 ± 3.05] × - + [170.36 ± 2.68]: [mean ± SEM]; P < 0.05), while 2 patients showed no improvement of oxygenation index (slope of regression SP/PP: 42.96/-22.70 and -11.63/-19.33). Renal failure of these two non-responders was not treated by HF. Improvement of oxygenation index was independent of duration in supine before the begin prone position (range 6 to 417 h). In one patient PP was started actually after 417 h of treatment at our Intensive Care Unit.

Conclusion

Starting prone position seems to mark a U-turn for oxygenation for the majority of patients with severe ARDS, while application of high fractional inspired oxygen, inverse ratio ventilation, positive end exspiratory pressure as well as kinetic therapy and hemofiltration do not necessarily improve oxygenation. The timing of this non invasive technique primarily depends on the decision to turn the patient from supine to prone. We recommend prone position in ARDS as soon as possible to reduce lung injury and complications resulting of mechanical ventilation.