Abstract
The effects of 1.0 and 1.5 minimum alveolar concentrations (MAC) of isoflurane on mean systemic arterial pressure, heart rate, stroke volume, cardiac output, total body oxygen consumption, myocardial oxygen consumption, and regional distribution of blood flow were studied in newborn lambs. Fractional extraction of oxygen for the total body and for the myocardium were calculated. MAC for isoflurane was first determined in eight lambs less than 10 days old. The mean value obtained was 1.51%. Six different lambs were used for cardiovascular study. Heart rate, stroke volume, cardiac output, and mean systemic arterial pressure decreased significantly during isoflurane anesthesia. Mean systemic arterial pressure and cardiac output decreased in a dose-dependent manner. Heart rate decreased significantly at 1.0 MAC isoflurane, but no further at 1.5 MAC. Stroke volume decreased only at 1.5 MAC. Cardiac output and total body oxygen consumption decreased by similar amounts at 1.0 MAC. Although cardiac output fell further at 1.5 MAC, oxygen consumption did not. Fractional extraction of oxygen increased only at 1.5 MAC. Myocardial blood flow and oxygen consumption decreased in parallel at 1.0 MAC, with no significant change during 1.5 MAC. Myocardial fractional oxygen extraction did not change. Although blood flow to all six body regions decreased significantly from control at both concentrations of isoflurane, blood flow to all organs except the adrenal did not differ significantly during 1.0 and 1.5 MAC. The authors conclude that a decrease in oxygen requirement during isoflurane anesthesia results in an appropriate decrease in oxygen delivery, with no apparent diversion of cardiac output from non-vital to vital organs.(ABSTRACT TRUNCATED AT 250 WORDS)
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