Changes in oxygenation and compliance as related to body position in acute lung injury

Body positioning during mechanical ventilation for acute lung injury has not been studied in a detailed manner. We evaluated the relationship between oxygenation, compliance, and body position during mechanical ventilation of patients with acute lung injury (ALI). Sixteen patients on mechanical ventilation with a diagnosis of ALI (partial pressure of oxygen/fraction of inspired oxygen <300 and no clinical evidence of congestive heart failure) were prospectively studied. Each patient was placed in a supine position followed by a 30 degrees head elevation and a 45 degrees head elevation. Data obtained in each position (after a 45-60 minute equilibration time) included static pulmonary compliance and partial pressure of oxygen from arterial blood gas sampling. Oxygenation is not improved and compliance is adversely affected by upright body positioning as compared to the supine position in patients receiving mechanical ventilation for ALI.