THE EFFECTS OF MULTIPLE SMALL DOSES OF EXOGENOUS SURFACTANT ON EXPERIMENTAL RESPIRATORY-FAILURE INDUCED BY LUNG LAVAGE IN RATS

Aim: To test the effect on pulmonary gas exchange and mechanics of mul tiple small doses of exogenous surfactant as an alternative to bolus d elivery in experimental respiratory failure induced by lung lavage. Me thods: After anesthesia, tracheostomy and constant volume ventilation, respiratory failure was induced by lung lavage in 20 rats. Animals we re randomly assigned to an untreated control group or two experimental groups. Equal total doses of modified porcine surfactant (200 mg . kg (-1) body weight,) were given by tracheal instillation, either as a si ngle bolus or in four (50 mg . kg(-1) b.w.) fractional doses at 10-min intervals. Arterial pH and blood gases, and peak inspiratory pressure (PIP) were measured. Results: After lavage, a rapid decrease in arter ial pH and PaO2, and an increase in PaCO2 and PIP were observed in all animals. In bath surfactant-treated groups, PaO2 increased after surf actant instillation, and remained significantly higher than controls t hroughout the experiment. Arterial pH was significantly higher and PaC O2 significantly lower only in the single bolus group. In the multiple dose group, these levels were similar to those of controls. Conclusio ns: In surfactant-depleted rats with respiratory failure, instillation of four fractional surfactant doses did not result in the same enhanc ement on gas exchange and PLP, in the following 60 min, as same total dose given by a single bolus.