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Preterm rabbit fetuses, delivered on the 27th day of gestation, were studied following upper airway instillation with either natural surfactant (NSA) obtained from the lavage of adult rabbit lungs or with a protein-free suspension of lipids extracted from lung wash (ESA). First, lung compliance was studied postmortem. The administration of 25 microliters of either preparation resulted in greater hysteresis (P less than 0.05) than was observed in control fetuses receiving no surfactant material. Increasing the phospholipid concentration stepwise from 10 to 50 mg/ml improved airway expansion and stability. No further improvement was encountered with concentrations greater than 50 mg/ml. There was no significant difference in compliance response between NSA and ESA. Morphometry of the lungs also indicated that the two preparations had an equal effect on compliance. Second, it was determined how neonatal survival was affected by a pharyngeal deposition, prior to the first breath, of 50 microliters NSA or ESA. Both treatment groups demonstrated improved survival (P less than 0.001) when compared with controls receiving no pharyngeal deposition. These findings offer further support to the concept that protein is not required for the efficacy of a surfactant supplementation. The equivalence of the two preparations suggests that a sterile suspension of a protein-free surfactant extract could be used to prevent or treat respiratory distress in preterm neonates.

Six preterm infants with severe hyaline membrane disease requiring ventilation were treated, at a median age of 15.5 hours, with a single intratracheal bolus of a bovine surfactant suspension. Arterial oxygenation increased dramatically, and chest radiograms showed improvement after two to four hours. However, a variable degree of deterioration occurred within 24 hours. All of the infants required oxygen therapy for several weeks, and one developed severe bronchopulmonary dysplasia.

The incorporation of intraperitoneally injected 3H-glycerol and 14C-palmitate into the lipids of lung, liver and brain was examined in premature rabbits (27 days gestation, term 31) both in utero and in control or surfactant-treated neonates. With the lung, there was an increased incorporation after delivery, especially with the surfactant-treated pups. The incorporation of 3H-glycerol into liver lipids was markedly reduced after birth, particularly with the nontreated controls. The liver:lung ratios of the incorporations were decreased after delivery. In all three tissues, the relative incorporations into the individual lipids were not affected to any great extent by birth or surfactant treatment. In lung, the disaturated and monoenoic species, respectively, of phosphatidylcholine accounted for the major proportion of the radioactivity. After birth there was a small increase in the labelling of the monoenoic species at the expense of the disaturated species with both control and surfactant-treated neonates. These observations support the proposal that surfactant treatment of the prematurely delivered neonate could be used prophylactically for the prevention of the respiratory distress syndrome.

Six preterm infants with severe hyaline membrane disease requiring ventilation were treated, at a median age of 15.5 hours, with a single intratracheal bolus of a bovine surfactant suspension. Arterial oxygenation increased dramatically, and chest radiograms showed improvement after two to four hours. However, a variable degree of deterioration occurred within 24 hours. All of the infants required oxygen therapy for several weeks, and one developed severe bronchopulmonary dysplasia.