The effect of hypopnea on low-pressure pulmonary edema.

The effects of the mechanical factors involved in ventilation on pulmonary edema are only partially understood. To clarify the effect of ventilation on the adult respiratory distress syndrome (ARDS), we examined the effect of reducing rate and tidal volume on oleic acid-induced low-pressure pulmonary edema in dogs, hypothesizing that hypopnea would reduce lung edema. We placed the experimental animals on venous-venous extracorporeal membrane oxygenation (ECMO) for CO2 clearance and oxygenation 1 h after the injury. This allowed reduction of the ventilatory rate from 17.2 +/- 4.8 to 3.3 +/- 0.8 breaths/min and tidal volume from 20 to 16 ml/kg, effectively resting the injured lung. After 5 h of hypopnea there was no reduction in edema by gravimetric or extravascular thermal volume measurements. The ECMO-facilitated hypopnea reduced airway pressure and pulmonary artery pressure while improving arterial oxygen saturation but increased venous admixture. These results suggest that there may be a supportive role for ECMO-assisted hypopnea, but there was no direct beneficial effect of hypopnea on edema.