Effects of exogenous surfactant on acute lung injury induced by intratracheal instillation of infant formula or human breast milk in rabbits

Abstract

Background: An animal experimental model or acute lung injury after intratracheal instillation of acidified milk products has been recently demonstrated. Exogenous administration of surfactant has proved to be successful treatment for acute lung injury induced by many causes including acid aspiration. The authors conducted this study to investigate whether exogenous surfactant can reduce the magnitude of lung damage induced in rabbits by acidified milk products. Methods: The lung injury was induced by intratracheal instillation of acidified human breast milk or acidified infant formula (0.8 ml/kg, pH 1.8). Thirty minutes after the insult, some animals were treated with intratracheal surfactant 100 or 200 mg/kg. Lung compliance and alveolar-to-arterial oxygen gradient were recorded during ventilation. After 4 or 12 h, the lungs were excised to determine physiologic and histologic lung damage. Albumin, interleukin-8, and eicosanoids in bronchoalveolar lavage fluid and superoxide production by neutrophils were measured. Results: The acidified milk products increased A-aD(O2) (550 ± 52 and 156 ± 28 mmHg; mean ± SD at 4 h in saline solution and infant formula groups, respectively), lung wet-to-dry weight ratio (6.6 ± 0.5 and 5.6 ± 0.2), % neutrophils in bronchoalveolar lavage fluid (84 ± 4% and 8 ± 2%), and decreased compliance (0.76 ± 0.09 and 1.90 ± 0.11 ml/cm H2O). Surfactant improved these variables in a dose-dependent manner (A-aD(O2) = 363 ± 50 and 237 ± 55 mmHg in 100-mg/kg and 200-mg/kg surfactant groups). Surfactant attenuated extensive histologic changes caused by the milk products. Superoxide production was less in rabbits receiving surfactant than in those not receiving it. Conclusion: Exogenous surfactant improved physiologic, histologic, and biochemical lung injury induced by acidified milk products in a dose-dependent manner. The effectiveness of surfactant may be caused, in part, by inhibition of neutrophils' sequestration and activation. These data indicate that intratracheal instillation of surfactant may be a promising therapeutic modality in acute lung injury resulting from aspiration of acidified milk products.