The Quantity of Natural Surfactant Necessary to Prevent the Respiratory Distress Syndrome in Premature Lambs

Abstract

Summary: Premature lambs at 118 to 122 days of gestation were delivered by caesarean section and received before the first breath 0, 19, 53 or 64 mg natural surfactant total lipid (TL) per kg body weight (BW). The seven lambs receiving no surfactant died within 40.1 ± 7.5 min, whereas the lambs treated with surfactant survived the 2-hr experimental period. Nineteen mg surfactant TL per kg BW preserved lung function; the pH and blood gas measurements were similar to those measured in lambs receiving 53 mg TL per kg BW or more surfactant. Pressure volume and surface tension characteristics were significantly improved after the administration of 19 mg of surfactant, but surface activity was still poor when compared to lambs receiving 53 mg TL per kg BW or more surfactant. The dose of surfactant (53 mg TL per kg BW) that resulted in good surface activity measurements in vitro was similar to other estimates of the amount of surfactant necessary to cover the alveolar space. Speculation: Differences were observed in the quantities of surfactant needed to normalize the clinical status and the pressure-volume and surface balance characteristics of the excised lungs and lung extracts. This may indicate that clinical status is the better way to evaluate the surfactant replacement therapy.