RESUSCITATION WITH 21% OR 100% OXYGEN IS EQUALLY EFFECTIVE IN RESTORING PERFUSION AND OXYGEN METABOLISM IN THE LIVER OF HYPOXIC NEWBORN PIGLETS

Abstract

The differential effects of the use of high or low oxygen levels during resuscitation on the neonatal liver are unknown. We compared the hepatic hemodynamics and oxygen metabolism in hypoxic newborn piglets resuscitated with 21% or 100% oxygen. Twenty-seven piglets (age, 1-3 days; weight, 1.5-2.0 kg) were acutely instrumented to measure cardiac output, hepatic artery, and portal venous blood flows (hepatic artery flow index [HAFI] and portal venous flow index [PVFI], respectively). The animals underwent 2 h of hypoxia (fraction of inspired oxygen, 0.10-0.15), then reoxygenation with 21% (n = 9) or 100% (n = 9) oxygen for 1 h, then 1 h with 21% oxygen. The controls (n = 9) were sham-operated without hypoxia-reoxygenation. Oxygen transport and plasma lactate concentrations were studied. Hypoxic animals had hypotension and decreased cardiac index with metabolic acidosis (mean pH, 7.00-7.02; P < 0.05 vs. controls). The PVFI and the total hepatic blood flow (THFI = PVFI + HAFI), despite the absence of significant change in HAFI, decreased to 16 +/- 2 mL/min/kg and 19 +/- 3 mL/min/kg, respectively (versus 24 +/- 2 mL/min/kg and 28 +/- 2 mL/min/kg of controls; P < 0.05). Fifteen minutes after reoxygenation, the cardiac index improved, PVFI recovered, HAFI was maintained, and THFI was not different between the groups. The hepatic oxygen consumption decreased (59%; P < 0.05) and the extraction increased (89%; P < 0.001) during hypoxia. Similarly, on reoxygenation, the hepatic oxygen consumption improved; however, extraction decreased versus controls on 100% but not on 21% oxygen (P < 0.05). The plasma lactate concentrations increased in both groups with hypoxia and were not different during reoxygenation between the group administered with 21% oxygen and the group administered with 100% oxygen. The hypoxic neonatal liver has reduced hepatic blood flow but has relatively preserved HAFI, and oxygen consumption recovered similarly on reoxygenation with 21% and 100% oxygen. The increased oxygen extraction during hypoxia normalized in 21% but reduced in 100% reoxygenation, with no differences in plasma lactate concentrations.