Temporal effects of prolonged hypoxaemia and reoxygenation on systemic, pulmonary and mesenteric perfusions in newborn piglets

Objective: Temporal effects of prolonged hypoxaemia and reoxygenation, on the systemic pulmonary and mesenteric circulations in newborn piglets, were investigated. Methods: Two groups [control (n=5), hypoxaemic (n=7)] of 1-3 day old anaesthetised piglets were instrumented with ultrasound flow probes placed to measure cardiac, hepatic arterial flow and portal venous flow indices, and catheters inserted for measurements of systemic and pulmonary arterial pressures. Hypoxaemia with arterial oxygen saturation 40-50% was maintained for 3 h, followed by reoxygenation with 100% inspired oxygen. Results: Cardiac index was transiently elevated at 30-60 min of hypoxaemia (23% increase from baseline 158+/-39 ml/kg/min), along with increases in stroke volume but not heart rate. A significant decrease in systemic vascular resistance after 30 min of hypoxaemia was followed by hypotension at 180 min of hypoxaemia. Progressive pulmonary hypertension with significant vasoconstriction was found after 30 min of hypoxaemia, The hypoxaemic mesenteric vasoconstriction was transient with a 37% decrease in portal venous flow index at 15 min of hypoxaemia (29+/-12 vs. 46+/-18 ml/kg/min of baseline, p<0.05). The hepatic arterial to total hepatic oxygen delivery ratio increased significantly during hypoxaemia, In contrast to the significant increase in systemic oxygen extraction throughout hypoxaemia, elevation in mesenteric oxygen extraction decreased after 30 min of hypoxaemia associated with modest decreases in oxygen consumption. Following reoxygenation, the pulmonary hypertension was partially reversed. Cardiac index decreased further (130+/-39 ml/kg/min) with reduced stroke volume, persistent systemic hypotension and decreased systemic oxygen delivery. Conclusions: We demonstrated differential temporal changes in systemic, pulmonary and mesenteric circulatory responses during prolonged hypoxaemia. Cautions need to be taken upon reoxygenation because the neonates are at risk of developing myocardial stunning, persistent pulmonary hypertension and necrotising enterocolitis. (C) 1998 Elsevier Science B.V. All rights reserved.