PRE-VENTILATORY VERSUS POST-VENTILATORY SURFACTANT TREATMENT IN SURFACTANT-DEFICIENT PRETERM LAMBS

Twenty lambs at 127 days' gestation (term is 145 days) were randomly a ssigned to receive Infasurf (Calf Lung Surfactant Extract, ONY Inc., A mherst, NY) as an intratracheal bolus (3 mL kg(-1)) either into a flui d-filled lung before ventilation (n = 10), or after ventilation for 5 min (n = 10). All lambs were surfactant-deficient by analysis of lung liquid obtained before surfactant administration. Lambs were then mech anically ventilated for 4 h. Oxygenation for the lambs given surfactan t before ventilation did not change during the experiment; a/A pO(2) w as 0.50 +/- 0.13 at 1 h and 0.52 +/- 0.17 at 4 h. For the lambs given surfactant after initial ventilation, oxygenation decreased over time; a/A pO(2) decreased from 0.48 +/- 0.23 at 1 h to 0.37 +/- 0.22 at 4 h (P < 0.05). Compliance, as calculated from the Ventilator Efficiency Index (VEI), improved over time in both groups, but was always signifi cantly higher for lambs given surfactant before ventilation (P = 0.03) . Histologic examination of the lungs revealed no differences between the groups; no evidence of epithelial denudation or hyaline membrane f ormation was seen in either group. Thus, ventilation of surfactant-def icient newborn lambs for 5 min before surfactant administration result s in significantly decreased lung function when compared with surfacta nt administration before ventilation. These differences in lung functi on are not dependent on a histopathologic injury to the lung. It is po ssible that unevenness of deposition of the surfactant in an air-fille d lung, compared to more uniform deposition in a fluid-filled unventil ated lung, produces these differences.