Surfactant phosphatidylcholine metabolism in neonates with meconium aspiration syndrome

Objective

Because meconium directly inhibits surfactant function, we sought to determine the effect of meconium on endogenous surfactant synthesis and clearance.

Study design

We studied surfactant phosphatidylcholine kinetics with the use of stable isotopes in 11 newborn infants with meconium aspiration syndrome (MAS) who required extracorporeal membrane oxygenation (ECMO). For comparison we studied 6 neonates with persistent pulmonary hypertension (PPHN) on ECMO and 10 term neonates ventilated for non-pulmonary indications and not on ECMO. All patients received a 24-hour [U-¹³C]glucose infusion as precursor for the palmitic acid in surfactant phosphatidylcholine.

Results

In the meconium group, the maximal ¹³C-incorporation in phosphatidylcholine (PC) was half of that in controls (0.09 ± 0.01 vs 0.18 ± 0.03 atom percent excess [APE], P = .027). There was a trend toward lower surfactant synthesis in the MAS group (3.3 ± 0.7%/day) and PPHN group (2.6 ± 0.3%/day) compared with controls 8.0 ± 2.4%/day, P = .058). Significantly lower PC concentrations in tracheal aspirates were found in the MAS group (4.4 ± 2.6 mg/mL) and PPHN group (3.6 ± 2.0 mg/mL) compared with controls (12.8 ± 2.6 mg/mL, P = .01). Endogenously synthesized surfactant had a similar half-life in all groups, ranging from 63 to 98 hours.

Conclusion

We conclude that surfactant synthesis is disturbed and that surfactant PC concentrations are low in infants with MAS on ECMO.

Abbreviations: ANOVA, Analysis of variance, APE, Atom percent excess, ASR, Absolute synthesis rate, AaDO₂, Alveolar-arterial oxygen tension difference, BAL, Bronchoalveolar lavage, ECMO, Extracorporal membrane oxygenation, E_gluc, Enrichment of plasma glucose, ELF, Epithelial lining fluid, E_max, Maximum enrichment, FSR, Fractional synthesis rate, MAP, Mean airway pressure, MAS, Meconium aspiration syndrome, OI, Oxygenation Index, PC, Phosphatidylcholine, PPHN, Persistent pulmonary hypertension of the newborn, SP-A, Surfactant protein-A, T_app, Time of first appearance of the label, T_max, Time of maximal enrichment