Prediction of the acute response to surfactant therapy by pulmonary function testing

We tested the hypothesis that pretreatment pulmonary function values would be predictive of the response to the synthetic pulmonary surfactant, Exosurf (Burroughs Wellcome Co.) treatment of infants with respiratory distress syndrome (RDS). Pulmonary compliance and resistance were measured prior to Exosurf treatment in 40 infants with severe RDS. In 36 patients who survived for at least 24 hr the acute response to therapy was quantitated by calculated post-treatment/pretreatment ratios of ventilator efficiency index (VEI) and arterial/alveolar oxygen tension ratios [Pa/AO2]. The values of these calculated response ratios 24 and 48 hr after treatment varied widely among individual patients. The magnitude of the response was not related to birthweight, gestational age, age at treatment, pretreatment VEI, pretreatment Pa/AO2, or pretreatment pulmonary compliance. However, the response to Exosurf as measured by improvements in Pa/AO2 at 24 and 48 hr was related to pretreatment pulmonary resistance (r = -0.34, P less than 0.05 and r = -0.60, P less than 0.001), high pretreatment pulmonary resistance was associated with a poor response to Exosurf 24 and 48 hr after treatment.