The oxygenation variations related to prone positioning during mechanical ventilation: a clinical comparison between ARDS and non-ARDS hypoxemic patients

Objectives: To compare, in clinical practice, the oxygenation variations related to prone positioning (PP) during mechanical ventilation in ARDS and non-ARDS hypoxemic patients. Design and setting: Prospective observational study of data on consecutive patients treated with the same protocol in the intensive care unit (ICU) of a university hospital. Patients: From May 1996 to December 1998, 226 PP periods without adjunction of nitric oxide (NO) inhalation and/or almitrine bismesylate infusion, performed in 59 mechanically ventilated hypoxemic patients (arterial oxygen tension/fractional inspired oxygen (PaO2/FIO2) ratio <300 mmHg) with no evidence of left ventricular failure, were included in this study. Measurements: Arterial blood gas was measured before the PP, at 1 h from the beginning of the PP, at the end of the PP and 1 h after returning to the supine position. Results: We analyzed 136 PP periods in 34 non-ARDS patients (60.2%) and 90 in 25 ARDS patients. The PP was repeated and the duration of the PP periods was: 10.6±0.22 h. The PP during the mechanical ventilation appeared to be safe and well tolerated. A PaO2/FIO2 ratio improvement at the end of the PP period, occurred for 196 periods (86.7%) with a mean PaO2/FIO2 ratio increase of +46.4±0.03% at the end of the PP periods compared to the baseline supine value. The PaO2/FIO2 ratio variations at 1 h after the start of the PP, at the end of the PP period and at 1 h after the return to supine were not different in ARDS or non-ARDS hypoxemic patients. The PaO2/FIO2 ratio improvement appeared to be more intense and more rapid in ARDS patients. Conclusions: In about 90% of periods, PP improved the PaO2/FIO2 ratio in patients with ARDS as well as in hypoxemic patients with non-ARDS. Studies are necessary to determine the impact of PP on survival and the mechanical ventilation duration in ARDS or non-ARDS hypoxemic patients.