Impairment of surfactant activity and ventilation by proteins in lung edema fluid

We investigated the effects of lung edema protein on ventilatory mechanics with special reference to surfactant activity. The edema fluid was obtained from hyperoxia-exposed adult rabbits. In immature newborn rabbits that could not be artificially ventilated at an insufflation pressure of 25 cm H2O, mean tidal volumes of > 27 ml/kg were obtained by supplementation with a natural surfactant (S-alone) or natural surfactant mixed with lung edema fluid (EF), the edema protein-to-surfactant ratio of which was < or = 5.6. A mixture with a ratio of 11.2 (11.2-EF/S), however, decreased the volume to 10.9 ml/kg (P < 0.05 vs S-alone). Surfactant mixed with isolated albumin at a concentration equal to that in 11.2-EF/S decreased the tidal volume to 8.6 ml/kg (NS vs 11.2-EF/S), and with isolated fibrinogen lowered it to 18.1 mg/kg (P < 0.05 vs S-alone). We conclude that lung edema fluid impairs ventilation through surfactant inactivation when the protein-to-surfactant ratio increases, and that albumin and fibrinogen are the main causes of this impairment.