ABSTRACT
The deliberate hypotension with esmolol or sodium nitroprusside(SNP) was provided subsequently in random order with six dogs. Anesthesia was maintained with 0.8 vol% halothane, end-tidal, in N2O/O2, 50: 50, with vecuronium. Mean arterial pressure was reduced 30-35% to 70 mmHg, with use of SNP or esmolol. Mean arterial pressure, heart rate, mean pulmonary arterial pressure, arterial blood gas analysis, and cardiac output were measured both prior to the deliberate hypotension and at 70 mmHg of mean arterial pressure induced with esmolol or SNP. The following results were observed; 1) The mean doses required were 725+/-250 ug/kg/min in esmolol and 12+/-2 ug/kg/min in SNP. 2) Esmolol was associated with a decrease in cardiac output (from 2.13+/-0.23 to 1.27+/-0.23 L/min), in heart rate (from 128+/-14 to 91+/-11/min), and an increase in central venous pressure (from 9.2+/-3.27 to 11.60+/-3.21 mmHg)(p<0.05). 3) SNP decreased systemic vascular resistance from 41111+/-484 to 2175+/-451 dynessec/cm5 (P<0.05), trended to increase heart rate. 4) A change in arterial blood gas analysis before and during deliberate hypotension with esmolol or SNP was not significant. As to mechanism of hypotensive effect, SNP caused decrease in systemic vascular resistance by 47% but esmolol significantly reduced cardiac output by 40% and heart rate by 29%. The result of present study suggests that when moderately deliberate hypotension with only esmolol was done, the potential for marked myocardial depression must be recognized. The differences in pharmacologic properties for the different hypotensive agents suggest that combinations of these agents may be provide a pharmacologic profile superior to either agent alone.