Abstract
Cardiovascular effects of nitrous oxide during enflurane anesthesia were studied in 12 healthy, young volunteer subjects ventilated to maintain normal PaC0]. Twelve circulatory variables were measured and 13 more calculated. When nitrogen, 70 per cent, was added to enflurane, 1.86 per cent (1 MAC), or enflurane, 2.93 per cent end-tidal, no change was observed. When nitrous oxide, 70 per cent, was added, only minimal changes were observed. In a second part of the study, enflurane was compared with enflurane-nitrous oxide, 70 per cent, at equipotent levels. The following three variables (in percentages) decreased less in relation to awake control values at 1 MAC enflurane-nitrous oxide-oxygen than at 1 MAC enflurane-oxygen: left ventricular stroke work, -47.2 vs. -55.9; aortic dP/dt, -44.0 vs. -57.1; pressure- pulse product, -26.6 ns. -39.4. Forearm venous compliance decreased more: -26.0 vs. 2.9. The difference between the anesthetic mixtures was much more noticeable at 1.5 MAC, where eight variables (in percentages) decreased less with enfluranenitrous oxide-oxygen than with enflurane-oxygen: cardiac output, -6.9 vs. -22.1; stroke volume, -31.4 ns. -46.0; left ventricular minute work, -32.6 vs. —49.6; left ventricular stroke work, -50.8 vs. -65.8; left ventricular stroke power, -48.2 us. -63.1; ballistocardiogram, -34.5ns. -49.1; aortic dP/dt, -49.7ns. -65.8; pressure-pulse product, -32.3 vs. -42.3. Heart rate increased less when nitrous oxide was included in the mixture: 34.5 ns. 43.6. The lack of response during the addition of nitrous oxide to enflurane-oxygen is contrary to the significant sympathomimetic response seen when nitrous oxide is added to halothane, fluroxene, or diethyl ether. The apparent protection afforded by nitrous oxide at equipotent anesthetic levels is small enough that the main consideration in choosing between the two mixtures should be the concentration of oxygen needed by the patient.
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