143 MYOCARDIAL METABOLIC AND HEMODYNAMIC CHANGES DURING ACUTELY INDUCED ASPHYXIA IN FETAL LAMBS

Abstract

Two days after instrumentation, we measured heart rate (HR), arterial blood pressure (BP), left ventricular myocardial blood flow (MBF), and myocardial consumption of oxygen, glucose and lactate in 6 fetal sheep (118-128 days gestation) in utero during acute progressive asphyxia induced by gradual constriction of a common uterine artery snare. Ascending aortic blood oxygen content decreased by 70% from 7.5 to 2.2 ml/dl. Ascending aortic blood oxygen saturation fell from 60% to 15%. pH fell from 7.40 to 7.04, while PCO2 increased from 46 to 72 torr. Coronary sinus PO2 fell from 11.6 to 6.6 torr. MBF increased 317% above the control of 239 ml/100g/min. Hemoglobin concentration was maintained from 9.3 to 10.8 g/dl during the study. HR, BP, and rate-pressure product remained unchanged. Myocardial oxygen consumption and extraction were maintained until an arterial oxygen saturation of 20-25%, after which they decreased. During hypoxemia, myocardial glucose consumption markedly increased and net lactate uptake by the myocardium occurred until an arterial PO2 of 12 torr (O2 saturation of 21%) was reached. Below this level lactate production occurred in 3 of 6 fetuses. Thus the fetal lamb has a marked reserve to increase myocardial blood flow and maintain myocardial oxygenation and substrate delivery during acute severe asphyxia.