Abstract 14: Pulmonary Hemodynamics in Neonatal Lambs with Pulmonary Hypertension - Effect of Resuscitation with 21% versus 100% Oxygen

Abstract

The optimal level of O 2 supplementation during neonatal resuscitation is controversial. We recently published data that resuscitation with 21% or 100% O 2 for 30 min results in similar decreases in pulmonary vascular resistance (PVR) in normal newborn lambs ( Pediatr Res in press) . However, the effect of resuscitation with 21% or 100% O 2 on pulmonary hemodynamics in lambs with in-utero pulmonary hypertension (PH) is not known. Methods: PH was induced in fetal lambs by antenatal ductal ligation at 126 d of gestation (term ~ 145 d). Lambs were delivered 9 d later by C-section and ventilated with 21% O 2 or 100% O 2 for 30 min. Control lambs without PH were ventilated similarly for comparison (n=4 −7 in each group). The lambs were instrumented to measure PVR prior to delivery. After 30 min, lambs with PH were ventilated with 50% O 2 and pulmonary vasodilator responses to inhaled NO 20 ppm were evaluated. Results: PVR was significantly higher in lambs with PH compared to control. The decrease in PVR was similar by 30 min in 21% and 100% O 2 resuscitated control lambs. In contrast, 100% O 2 resuscitation resulted in a significantly greater decrease in PVR in lambs with PH (fig A ). However, 100% O 2 resuscitation impaired subsequent decrease in PVR in response to inhaled NO in both control and PH lambs (fig B ). Conclusions: 100% O 2 resuscitation results in a greater decrease in PVR but impairs subsequent pulmonary vasodilation to NO in lambs with PH. Speculation: Ventilation of PH lambs with 100% O 2 significantly increases lung isoprostane levels ( AJRCCM 2006 174 12:1370 ). We speculate that a similar increase in reactive oxygen species following 100% O 2 resuscitation interferes with the vasodilator response to NO.