SURFACTANT REPLACEMENT THERAPY IMPROVES VENTILATION INHOMOGENEITY IN INFANTS WITH RESPIRATORY-DISTRESS SYNDROME

Surfactant deficiency in newborn infants with hyaline membrane disease (HMD) reduces peripheral airway stability, leading to lung atelectasi s, inhomogeneity of distribution of ventilation, ventilation/perfusion mismatch, and hypoxemia. The aim of this study was to evaluate the im mediate effect of exogenous surfactant treatment on Ventilation inhomo geneity (VIH) in infants with HMD. Homogeneity of ventilation was meas ured repeatedly in ten infants (median gestational age 30 weeks and bi rthweight 1.50 kg) after Exosurf(R), and in six infants (median gestat ional age 30 weeks and birthweight 1.42 kg) after Survanta(R) treatmen t. Lung function was measured before and 0.5, 2, and 6 hours after adm inistration of a single dose of surfactant. The multiple breath nitrog en washout method was used to measure the time pattern of nitrogen eli mination from the lungs. VIH was evaluated by using both a compartment al lung model and a model-independent moment analysis. The two-compart ment lung model was found to dominate before surfactant treatment, whi le a single-compartment model (implying homogeneous ventilation) fitte d the washout data best 6 hours after Exosurf(R) treatment (P < 0.01). The same pattern occurred 2 hours after Survanta(R) administration. M oment analysis confirmed the reduction in VIH by both surfactants. Thi s study supports the hypothesis that the improved oxygenation after su rfactant treatment in infants with HMD results from a reduction in VIH and an increase in functional residual capacity (FRC). (C) 1997 Wiley -Liss, Inc.