Mechanism by which the prone position improves oxygenation in acute lung injury, with NO inhalation or not: role of the bronchial drainage effect.

Objectives: A bronchial secretion draining effect is frequently suggested a s a mechanism for oxygenation improvement during prone positioning (PP) in patients with acute respiratory distress syndrome (ARDS). Nevertheless, it has never really been evaluated. The aim of this study was to search for an interrelationship between the volume of the bronchial secretion and the im provement of the PaO2/FIO2 ratio during prone positioning, with NO inhalati on or not. Study desing: Open prospective clinical study. Patients: The study included 15 consecutive patients with severe ARDS (PaO2 /FIO2 < 200 after alveolar recruitment, Murray score > 2,5). Methods: They were returned to the prone position for 4 hours (h0-h4) combi ned with an inhalation of 5 ppm NO during 1 hour (h2-h3). Tracheal suctions were performed hourly between h-2 and h6 and weighed on a precision scale from h-l to h6. Haemodynamic, blood gas and respiratory compliance were rec orded at h0, h2, h3, h4 and h6. Results: No significant haemodynamic changes were observed in the various p hases. Compared with the baseline condition at h0, PP and PP+NO respectivel y improved PaO2/FIO2 by 102 +/- 62% at h2 (P < 0.005) and 156 +/- 79% at h3 (P < 0.005/h0 and < 0.01/h2). 14/15 patients responded to PP and 15/15 to PP+NO (gain in PaO2/FIO2 > 10%). Concerning secretions, we collected 3.0 +/ - 7.5 g, 4.4 +/- 6.1 g, 1.7 +/- 1.4 g and 1,7 +/- 1,6 between h-2 and h0, h 0 and h2, h2 and h4, h4 and h6. Individual assessments showed no relationsh ip between the PaO2/FIO2, evolution at any time and the quantity of secreti ons obtained during the first 2 hours in the prone position. Six patients p resented secretions of less than Ig between h0 and h2, and for whom the imp rovement in oxygenation was higher than average (115 +/- 53% at h2). Conclusion: In patients with little or moderate secretions, the improvement observed in oxygenation, with or without NO, does not depend on their volu me. (C) 2000 Editions scientifiques et medicales Elsevier SAS.