Surfactant replacement reverses respiratory failure induced by intratracheal endotoxin in rats

Abstract

Objective To evaluate the effect of surfactant replacement on respiratory failure induced by intratracheal injection of endotoxin in rats. Design Prospective, randomized study. Setting Laboratory at a large university. Subjects Male Wistar rats, weighing 353 plus minus 50 (SD) g. Interventions Escherichia coli endotoxin (53 plus minus 19 mg/kg) was injected into the trachea of 32 rats anesthetized with pentobarbital and mechanically ventilated with an FIO₂ of 1.0. After PaO₂ decreased to less than 200 torr (less than 26.7 kPa), the rats were assigned to three groups: a) a surfactant group (n equals 16), given a modified natural surfactant suspension (100 mg/kg in 2.0 mL/kg of saline) by instillation into the airway; b) a saline control group (n equals 8), given 2.0 mL/kg of saline; and c) an air control group (n equals 8), given 2.0 mL/kg of air. An additional nine rats were ventilated in the same way but were not given endotoxin. Measurements and Main Results Among the rats receiving endotoxin, the PaO sub 2 of the saline and air control groups remained less than 200 torr (less than 26.7 kPa), while PaO₂ of the surfactant group increased to 390 plus minus 116 torr (52.0 plus minus 15.5 kPa; p less than .05 vs. the preassignment value) 15 mins after the assignment. These high levels were maintained throughout the experiment. Surfactant replacement also led to significant improvements in the PaCO₂, the dynamic lung-thorax compliance, the pressure-volume recordings of the lung, and the chest roentgenograms. Histologic examination showed that the alveoli of the surfactant group were better aerated than the alveoli of the control groups. Findings in the rats not given endotoxin were almost normal, indicating that the influences of mechanical ventilation were negligible. Conclusion Surfactant replacement reversed respiratory failure induced by intratracheal injection of endotoxin in rats. (Crit Care Med 1995; 23:149-156)