1271 PDA WITH SURFACTANT REPLACEMENT THERAPY

Abstract

Surfactant instillation into the trachea of preterm infants with RDS is associated with a 90% incidence of PDA. We studied the effects of surfactant therapy on the ductus arteriosus (DA) in 12 preterm lambs (.89 gestation). Flow (Q) across the DA and systemic blood flow were calculated from microsphere injections. All 12 lambs were paralyzed and ventilated with 100% O2. All developed respiratory failure (pH<7.1, PCO>60) by 30 min after birth. Between 30-60 mins after birth, 6 lambs were treated with tracheal instillation of 50 mg/kg surfactant lipid (purified from alveolar washes from adult sheep). There were no significant differences between control and treated animals prior to surfactant instillation for PCO2, pH, prostaglandin (PG) E2 concentrations, the ratio of L→R shunt through the DA vs systemic flow (Q shunt/Q syst), DA resistance, or the ratio of pulmonary to systemic vascular resistance (RP/RS). By 2 hr after birth treated lambs differed significantly from controls in pH (7.27±02 vs 6.97±08) and PCO2 (43.3±4.1 vs 85±15). There were no differences in PO2 (146±50 vs 84±44), PGE2 concentrations or DA resistance. However, there was a significantly larger shunt through the DA in treated lambs (Q shunt/syst=.70±.14 vs .25±10). This increased DA shunt was due to the significant drop in pulmonary vascular resistance (RP/RS=.47±.08 vs .76±.08) and not to a change in patency of the DA. Surfactant replacement may require interventions directed at the PDA to adequately treated sick preterm infants.