Cardiopulmonary effects of oleic acid-induced pulmonary edema and mechanical ventilation

In order to define the mechanisms whereby cardiac output and arterial oxygen transport are reduced by acute permeability pulmonary edema and by positive end-expiratory pressure (PEEP), hemodynamic, respiratory, and lung water changes were measured in 12 mechanically ventilated dogs prior to the injection of oleic acid and at 1, 2.5, and 4 hr after the injection. Measurements were performed at each interval before and after the addition of 20 cm H2O PEEP. Positive end-expiratory pressure was not continued between measurements. One hour after the oleic acid injection, the lung water content and the pulmonary vascular resistance had increased more than 100% while the right ventricular (RV) volume, RV stroke volume, and PaO2 had decreased more than 35%. Each application of PEEP increased the PaO2 to control levels. However, PEEP also significantly increased the lung water content and pulmonary vascular resistance, and decreased the RV volume and stroke volume by 33%. The extravasation of fluid from the intravascular to the interstitial and alveolar spaces of the lung with oleic acid pulmonary edema is associated with substantial decreases in right ventricular volume and stroke volume and significant increases in the pulmonary vascular resistance. Treatment with 20 cm H2O PEEP further increases the lung water content and pulmonary vascular resistance and substantially reduces the right ventricular volume and stroke volume.