Effects of surfactant replacement on irregular overdistension of meconium-injured lungs in rats

Overdistension of the lungs is a cause of ventilator-induced lung injury. In meconium aspiration syndrome, irregular overdistension of the lungs often occurs.

We investigated whether surfactant replacement could restore the terminal airspaces in the lungs that had been distended after meconium aspiration.

Meconium aspiration was induced by injecting meconium (50 mg x kg(-1)) into the airways of adult rats anesthetized with pentobarbital and ventilated with pressure-preset mode. The animals were further ventilated with or without surfactant replacement (100 mg x kg(-1)), and the sizes of the terminal airspaces were determined after fixing the lungs at an airway pressure of 10 cm H2O on deflation.

Approximately 75 min after aspiration (early analysis point), alveolar ducts were widened and the mean ratio of the largest terminal airspace size class (> or =63,000 microm(2)) was 38.7% (n = 7), which was significantly higher than that of controls (6%, n = 7). Three hours after the early analysis point, the ratio increased to 50.2% (n = 7, p < 0.05), but surfactant replacement reversed the ratio to 18.8% (n = 7, p < 0.05).

In rats with meconium aspiration, surfactant replacement restored the distended terminal airspaces of the lungs and kept the spaces from irregular overdistension.