Scintigraphy and radiography in oleic acid pulmonary microvascular injury: effects of positive end-expiratory pressure (PEEP).

Using computerized gamma scintigraphy, 10-cm H2O PEEP did not alter the rate of capillary protein leakage in dogs following pulmonary microvascular injury with 0.01 to 0.2 ml/kg oleic acid. A rising lung:heart radioactivity ratio, or 'slope of injury,' was seen during PEEP which paralleled the 'slope of injury' had PEEP not been used. A sudden decrease in lung and heart count activity (p less than 0.001) and decreased lung:heart radioactivity ratio (p less than 0.001) occurred with PEEP at all doses of oleic acid studied. An apparent improvement in the standard chest roentgenogram was seen within 2 minutes following PEEP in dogs given 0.2 ml/kg oleic acid. However, progression of the radiographic infiltrate occurred in these animals during 30 minutes of PEEP. When all vessels leading to and from the heart and lungs were ligated, PEEP produced a 60% fall in count activity over the lung without any change in cardiac radioactivity. The apparent radiographic improvement and 2/3 of the fall in lung radioactivity with PEEP were due to an increased pulmonary air volume and 1/3 due to a decreased pulmonary blood volume. The decreased cardiac output with PEEP must be secondary to decreased ventricular filling rather than decreased ventricular function.