Lung Regional Metabolic Activity and Gas Volume Changes Induced by Tidal Ventilation in Patients with Acute Lung Injury.

RATIONALE: During acute lung injury, mechanical ventilation can aggravate inflammation by promoting alveolar distension and cyclic recruitment-derecruitment. As an estimate of the intensity of inflammation, metabolic activity can be measured by positron emission tomography imaging of [(18)F]fluoro-2-deoxy-D-glucose. OBJECTIVE: To assess the relationship between gas volume changes induced by tidal ventilation and pulmonary metabolic activity in patients with acute lung injury. METHODS: In thirteen mechanically ventilated patients with acute lung injury and relatively high PEEP, we performed a positron emission tomography scan of the chest and three computed tomography scans: at mean airway pressure, end-expiration and end-inspiration. Metabolic activity was measured from the [(18)F]fluoro-2-deoxy-D-glucose uptake rate. The computed tomography scans were used to classify lung regions as derecruited throughout the respiratory cycle, undergoing recruitment-derecruitment, and normally aerated. MEASUREMENTS AND MAIN RESULTS: Metabolic activity of normally aerated lung was positively correlated both with plateau pressure, showing a pronounced increase above 26-27 cmH2O, and with regional tidal volume normalized by end-expiratory lung gas volume. This relationship did not appear to be caused by a higher underlying parenchymal metabolic activity in patients with higher plateau pressure. Regions undergoing cyclic recruitment-derecruitment did not have higher metabolic activity than those collapsed throughout the respiratory cycle. CONCLUSIONS: In patients with acute lung injury managed with relatively high end-expiratory pressure, metabolic activity of aerated regions was associated with both plateau pressure and regional tidal volume normalized by end-expiratory lung gas volume, while no association was found between cyclic recruitment-derecruitment and increased metabolic activity.