Experimental pulmonary edema: the effect of positive end-expiratory pressure on lung water

The effect of 10 cm of positive end-expiratory pressure (PEEP) on lung water was studied during pulmonary edema induced in dogs by inflating a Foley balloon placed in the left atrium. Colloid oncotic pressure (COP) was measured directly. Intrapleural pressure (IPP) was measured after surgical closure of the chest. Transmural left atrial (LA) pressure (LA minus IPP) minus COP was considered to be the net force driving water out of the capillaries. LA pressure was elevated so that transmural LA pressure minus COP averaged +7.5 mm Hg. Water accumulation was expressed as the ratio of wet to dry weight. The control ratio of wet to dry lung weight was 4.30 +/- 0.10 (+/- SE). After 2 hours of standardized pulmonary edema and ventilation without PEEP, wet-to-dry lung weight was 5.63 +/- 0.24. In animals ventilated with 10 cm of PEEP through 2 hours of pulmonary edema the ratio was 5.36 +/- 0.14. Animals ventilated with 10 cm of PEEP showed a significant increase in functional residual capacity and decreased intrapulmonary shunt. Ten centimeters of PEEP, however, had no statistically significant effect on water accumulation during experimental pulmonary edema.