Surfactant Replacement Improves Lung Recoil in Rabbit Lungs after Acid Aspiration

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Abstract
We tested the hypothesis that surfactant replacement would be beneficial in the acid-aspiration model of acute lung injury. HCl (0.1 N, 2 ml/kg) was injected into the trachea of excised rabbit lungs (n = 8). Control lungs (n = 4) had no intervention. All were perfused with Tyrode''s solution mixed 1:1 with autologous whole blood at 40 ml/min/kg for 30 min, and then degassed. A modified natural surfactant (Survanta, Ross Laboratories) was then injected into the trachea of four lungs injured with HCl (100 mg/kg at 25 mg/ml). Two quasi-static pressure-volume curves were determined. The mean alveolar pressures at 50, 60, 70, 80, and 90% of TLC were greater in the HCl group than in the control group (p < 0.05). However, no difference was observed between the control lungs and those that received HCl + Survanta. In 13 anesthetized, paralyzed, and ventilated rabbits, deflation pressure-volume curves were determined from TLC to FRC (measured by helium dilution). Then, 0.1 N HCl (3 ml/kg) was injected into the trachea and, in seven, Survanta was instilled 5 min later. The mean alveolar pressures at 60, 70, 80, and 90% TLC were higher at 15 and 60 min in the HCl group compared with their pre-HCl time point (P < 0.05). In the HCl + Survanta group, no differences were seen at 15 min, and only slight increases were seen at 60 min. No effect of surfactant replacement on arterial blood gases was observed. HCl aspiration increased recoil in both excised and in vivo lungs, and surfactant replacement with Survanta returned recoil to normal.