TEMPORAL EFFECTS OF PROLONGED HYPOXEMIA 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 pigl ets, were investigated. Methods: Two groups [control (n=5), hypoxaemic (n=7)] of 1-3 day old anaesthetised piglets were instrumented with ul trasound flow probes placed to measure cardiac, hepatic arterial flow and portal venous flow indices, and catheters inserted for measurement s of systemic and pulmonary arterial pressures. Hypoxaemia with arteri al oxygen saturation 40-50% was maintained for 3 h, followed by reoxyg enation with 100% inspired oxygen. Results: Cardiac index was transien tly elevated at 30-60 min of hypoxaemia (23% increase from baseline 15 8+/-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 hypoxaemi a. Progressive pulmonary hypertension with significant vasoconstrictio n was found after 30 min of hypoxaemia, The hypoxaemic mesenteric vaso constriction was transient with a 37% decrease in portal venous flow i ndex at 15 min of hypoxaemia (29+/-12 vs. 46+/-18 ml/kg/min of baselin e, p<0.05). The hepatic arterial to total hepatic oxygen delivery rati o increased significantly during hypoxaemia, In contrast to the signif icant increase in systemic oxygen extraction throughout hypoxaemia, el evation in mesenteric oxygen extraction decreased after 30 min of hypo xaemia associated with modest decreases in oxygen consumption. Followi ng reoxygenation, the pulmonary hypertension was partially reversed. C ardiac index decreased further (130+/-39 ml/kg/min) with reduced strok e volume, persistent systemic hypotension and decreased systemic oxyge n delivery. Conclusions: We demonstrated differential temporal changes in systemic, pulmonary and mesenteric circulatory responses during pr olonged hypoxaemia. Cautions need to be taken upon reoxygenation becau se the neonates are at risk of developing myocardial stunning, persist ent pulmonary hypertension and necrotising enterocolitis. (C) 1998 Els evier Science B.V. All rights reserved.