Alveolar fluid clearance in healthy pigs and influence of positive end-expiratory pressure

Introduction: The objectives were to characterize alveolar fluid clearance (AFC) in pigs with normal lungs and to analyze the effect of immediate application of positive end-expiratory pressure (PEEP). Methods: Animals (n = 25) were mechanically ventilated and divided into four groups: small edema (SE) group, producing pulmonary edema (PE) by intratracheal instillation of 4 ml/kg of saline solution; small edema with PEEP (SE + PEEP) group, same as previous but applying PEEP of 10 cmH(2)O; large edema (LE) group, producing PE by instillation of 10 ml/kg of saline solution; and large edema with PEEP (LE + PEEP) group, same as LE group but applying PEEP of 10 cmH(2)O. AFC was estimated from differences in extravascular lung water values obtained by transpulmonary thermodilution method. Results: At one hour, AFC was 19.4% in SE group and 18.0% in LE group. In the SE + PEEP group, the AFC rate was higher at one hour than at subsequent time points and higher than in the SE group (45.4% vs. 19.4% at one hour, P < 0.05). The AFC rate was also significantly higher in the LE + PEEP than in the LE group at three hours and four hours. Conclusions: In this pig model, the AFC rate is around 20% at one hour and around 50% at four hours, regardless of the amount of edema, and is increased by the application of PEEP.