Respiratory support, surface activity and protein content during nosocomial infection in preterm neonates.

Small volume bronchoalveolar lavages from 10 infants (26.6 +/- 0.4 weeks gestational age) during postnatal nosocomial infection were fractioned by differential centrifugation into large (LA) and small (SA) surfactant aggregates. Before deterioration of the clinical status, the surface tension at minimum bubble radius (gamma min), as measured in a pulsating bubble surfactometer, was reduced to about 14 mN/m by LA and to about 22 mN/m by the corresponding SA. The gamma min of both LA and SA increased during clinical deterioration, was highest at the worst clinical state and returned during recovery to values in the range before deterioration. Respiratory support significantly correlated to gamma min at all times. In contrast, no correlation was observed for total protein or albumin content of the LA or SA fractions. The SA fraction was characterized by a 10-fold higher protein content than LA. These data demonstrate functional impairment of surfactant in subfractions during mechanical ventilation and nosocomial infection in preterm neonates that are not fully explained by inhibition with increasing amounts of total protein.