Animal studies of surfactant replacement therapy.

Before using surfactant preparations in animal experiments or in clinical trials, it is necessary that they fulfil specific in vivo requirements. But conclusive criteria for the effectiveness of a surfactant have not yet been defined. Thus, some standard levels for improvement of lung function, or threshold levels, must be established in standardized animal models with surfactant deficiency. The respiratory distress syndrome model of premature rabbit fetuses is the most sensitive model, followed by the surfactant deficiency model by lung lavage, while the model of viral pneumonia is the least sensitive when testing exogenous surfactant. With a less-effective exogenous surfactat, a small improvement in lung function in the rabbit fetus model and the lung lavage model can be observed, while in the viral pneumonia model almost no improvement occurred. Only a functional effective surfactant fulfilled all our criteria for functional improvement in lung function.