Lung volumes and alveolar expansion pattern in immature rabbits treated with serumdiluted surfactant. acute respiratory distress syndrome, mechanical ventilation often induces alveolar overdistension aggravating the primary insult. To examine the mechanism of overdistension, surfactant-deficient immature rabbits were anesthetized with pentobarbital sodium, and their lungs were treated with serum-diluted modified natural surfactant (porcine lung extract; 2 mg/ml, 10 ml/kg). By mechanical

more »

... ion with a peak inspiration pressure of 22.5 cmH2O, the animals had a tidal volume of 14.7 ml/kg (mean), when 2.5 cmH2O positive end-expiratory pressure was added. This volume was similar to that in animals treated with nondiluted modified natural surfactant (24 mg/ml in Ringer solution, 10 ml/kg). However, the lungs fixed at 10 cmH 2O on the deflation limbs of the pressurevolume curve had the largest alveolar/alveolar duct profiles (Ն48,000 m 2 ), accounting for 38% of the terminal air spaces, and the smallest (Ͻ6,000 m 2 ), accounting for 31%. These values were higher than those in animals treated with nondiluted modified natural surfactant (P Ͻ 0.05). We conclude that administration of serum-diluted surfactant to immature neonatal lungs leads to patchy overdistension of terminal air spaces, similar to the expansion pattern that may be seen after dilution of endogenous surfactant with proteinaceous edema fluid in acute respiratory distress syndrome. acute respiratory distress syndrome; alveolar overdistension; dynamic surface tension; positive end-expiratory pressure