Lung Function in Prematurely Delivered Rabbits Treated with a Synthetic Surfactant

Abstract

We treated prematurely delivered rabbit pups with the synthetic surfactant that has been named Exosurf. By weight. Exosurf is 61.8% dipalmitoylphosphatidytcholine, 6.8% hexadecanol, 4.6% tyloxapol, and 26.7% NaCl. This simple mixture, suspended at 15 mg lipid-ml⁻¹ water, has appropriate in vitro characteristics for a lung surfactant substitute. As determined by static pressure volume relationships performed after 30 min ventilation, lungs treated with Exosurf accepted significantly more gas at maximal inflation (36 versus 15 ml-kg⁻¹ body weight) and had significantly greater volumes during deflation than did saline-treated control lungs; lungs treated with natural rabbit surfactant (SAM) had significantly larger volumes at maximal inflation (65 versus 35 ml-kg⁻¹) and during deflation than did the Exosurf-treated lungs. After 30 min of ventilation with oxygen and fixation at 10 cm H₂O pressure, the ratio of air space to tissue space was determined by a point-counting technique, and mean linear intercepts were measured for air spaces. Exosurf-treated lungs were intermediate between SAM and saline-treated lungs in both measurements. With positive pressure ventilation to maintain a tidal volume of 6.5 to 7.5 ml-kg- 1 , total compliance was significantly greater and inspiratory pressure significantly lower in both SAM- and Exosurf-treated animals than in saline-treated control animals, although the lungs of the SAM-treated animals were more compliant than the lungs of animals treated with Exosurf. During the first minute of positive pressure ventilation, lungs treated with SAM or Exosurf expanded equally rapidly, both expanding more rapidly than the saline-treated lungs. Pulmonary air leaks were more common in SAM-treated lungs than in lungs from Exosurf-treated animals. We conclude that Exosurf significantly improves lung function in rabbits born at 26 days and 20 h after mating when compared with saline-treated control animals.