Captopril Reduces the Dose Requirement for Sodium Nitroprusside Induced Hypotension

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Abstract
Patients [12] who required deliberate hypotension for spinal fusion operations were studied to investigate the efficacy of captopril for reducing dose requirement for sodium nitroprusside (SNP). Six patients, selected at random, were pretreated with captopril, 3 mg/kg po [orally], and the remaining 6 served as controls. All patients received a similar anesthetic technique, consisting of thiopental 3 mg/kg, pancuronium 0.1 mg/kg, morphine 0.5 mg/kg, plus N2O 70% in O2. SNP was used to maintain mean arterial pressure (MAP) at 50-55 mm Hg during deliberate hypotension lasting 140 .+-. 13 min (mean). Patients who received captopril required less SNP than untreated patients both early during hypotension (1.4 .+-. 0.5 vs. 4.8 .+-. 0.8 .mu.g/kg per min, P < 0.05), as well as late during hypotension (2.2 .+-. 0.2 vs. 5.6 .+-. 0.6 .mu.g/kg per min, P < 0.05). Whole blood CN- was significantly lower in the patients pretreated with captopril than the untreated controls both early in the hypotensive period (2.7 .+-. 0.6 vs. 13 .+-. 4 .mu.mol/l, P < 0.05) and also late in the hypotensive period (3.7 .+-. 0.8 vs. 30 .+-. 10 .mu.mol/l, P < 0.05). MAP was reduced by captopril pretreatment both following induction of anesthesia (64 .+-. 4 mm Hg captopril vs. 80 .+-. 4 mm Hg control, P < 0.05) and during surgery before deliberate hypotension (86 .+-. 5 mm Hg captopril vs. 100 .+-. 4 control, P < 0.05). Cardiac output did not differ significantly between the groups, either awake or after anesthetic induction. Evidently captopril pretreatment significantly reduces the dose of SNP required to produce deliberate hypotension and, therefore, reduces the potential for CN toxicity. No adverse hemodynamic consequences of combining captopril with thiopental, N2O or morphine anesthesia were observed.