Experimental Models of Acute Respiratory Distress Syndrome: Clinical Relevance and Response to Surfactant Therapy

Surfactant therapy for acute respiratory distress syndrome (ARDS) has shown encouraging results in animal studies, but not always in clinical trials. Efficacy of this therapy may be limited to ARDS caused by indirect injury, but mistiming of its application in clinical trials may be responsible for the discouraging results. In addition, the therapy may not last long enough to be effective. In rats with acidified milk aspiration, the effects of aerosolized surfactant therapy followed by inhalation of aerosolized dextran (molecular weight, 40,000) last significantly longer than those of aerosolized surfactant therapy alone. This mode of surfactant therapy could lead to better results since it can be started and repeated at any time.

Aerosolized surfactant therapy for endotoxin-induced experimental acute respiratory distress syndrome in rats

We have compared the effects of inhalation of aerosolized surfactant on experimental acute respiratory distress syndrome. Escherichia coli endotoxin (55 (SD 20) mg kg(-1)) was injected into the tracheas of 36 adult rats anaesthetized and mechanically ventilated with pure oxygen. When the Pa(O(2)) decreased to 11.3 (3.3) kPa, the animals were randomly subjected to inhalation of aerosolized modified natural surfactant (MNS) for 0 min (control group), 30, 60, and 120 min. In the control group, Pa(O(2)) remained below 12 kPa for 180 min. In the groups receiving inhalation of surfactant for 30 and 60 min, Pa(O(2)) increased but decreased soon after termination of the inhalation. In contrast, Pa(O(2)) of the group receiving inhalation of surfactant for 120 min continued to increase, reaching 52.1 (12.5) kPa at 180 min (P<0.05 vs control). Thus, we conclude that improvement in gas exchange as a result of inhalation of MNS depends on the duration of inhalation.