INTRODUCTION: Little is known about surfactant metabolism in newborn infants as radioactive isotopes cannot be used in humans. We used the stable isotope labelled dipalmitoylphosphatidylcholine (13C-DPPC) as tracer to study exogenous surfactant metabolism in preterm infants with RDS.

METHODS: We studied 8 preterm infants with RDS who required exogenous surfactant. Patients with proven infection were excluded. All infants received 100 mg/kg/dose of porcine surfactant (Curosurfr Chiesi, ITALY) as rescue treatment for RDS and 5 mg/kg/dose of 13C-DPPC as tracer. Birth weight was 1.2±0.2 kg and gestational age 29.0±2.7 wks. 13C-enrichment of palmitic acid of PC from tracheal aspirates was measured by gas chromatography-mass spectrometry every 12 hours until extubation. 13C-enrichment of plasma lipids and of the gastric content was also measured. Half-life was calculated from the mono-exponential part of the downslope of the enrichment-time-curve.

RESULTS: Half-life of the first (n=5) and second (n=6) surfactant doses was 39.8±25.9 and 48.9±33.7 hours respectively (p=0.38, NS). After endotracheal administration of surfactant with 13C-DPPC 13C-enrichment was found in the plasma lipids of all the studied infants and in the gastric content of 4 infants.

CONCLUSIONS: We present a novel and safe method to study exogenous surfactant kinetics in human infants. The half-lifes found in this study were slighly shorter than those obtained by us for endogenous surfactant in preterm infants with RDS. The marked differences found between patients warrant further investigations.