We studied the cardiovascular effects of enflurane in 12 unpremedicated volunteers without surgery under conditions of constant arterial CO, tension and body temperature. During the first hour of anesthesia 1 MAC (1.86% end-tidal) was associated with decreased cardiac output (CO) by 25.9%, stroke volume (SV) by 39.6%, systemic vascular resistance (SVR) by 16.1%, IJ wave of the ballistocardiogram (Beg) by 39%. and aortic dP/dt by 60.7% compared to awake values. Heart rate (HR) increased 22.4%, but blood pressure (BP) declined by 36%. Central venous pressure (CVP) rose less than 1 torr. Plethysmographic measurements of finger (skin) and forearm (muscle) blood flow did not significantly change from awake levels, but forearm vascular resistance was reduced. An increase to 1.5 MAC caused further declines in SV, aortic dP/dt, and Bcg, but not in BP or CO. Heart rate increased and the CVP rose 3.8 torr above control. Two MAC enflurane could not be achieved without progressive and profound hypotension.
During the sixth hour of continuous anesthesia, we observed some recovery of cardiovascular performance. Cardiac output, SV, and aortic dP/dt returned toward awake levels at 1 MAC, but not at 1.5 MAC. Systemic vascular resistance declined during the interval, and BP remained unaltered.
The margin of safety between concentrations of cnflurane required for surgical anesthesia and hazardous concentrations is less during controlled ventilation than is the margin of safety associated with other potent inhalation anesthetics.