SODIUM-NITROPRUSSIDE INDUCED HYPOTENSION - HEMODYNAMIC-RESPONSE AND DOSE REQUIREMENTS DURING PROPOFOL OR HALOTHANE ANESTHESIA

This study was designed to investigate the influence of anaesthesia in duced and maintained with propofol on the haemodynamic effects and the dose requirements of SNP during the course of induced hypotension. Tw enty-four adult ASA physical status I patients undergoing middle ear s urgery were randomly assigned to receive anaesthesia with either morph ine, thiopentone, d-tubocurarine, halothane 0.6% end-tidal and N2O 70% in oxygen (group I n =12), or morphine, propofol, d-tubocurarine, pro pofol infusion 108 mug.kg-1.min-1 and N2O in oxygen (group 2 n = 12). Mean arterial blood pressure (MAP) was reduced to 60-65 mmHg in all pa tients using a continuous infusion of sodium nitroprusside (SNP) 0.01% . Propofol produced a significant (17%) reduction in the MAP before in stitution of SNP infusion. This was related to a 24% reduction in the systemic vascular resistance index (SVRI). In the halothane group SVRI was significantly reduced during SNP infusion. Halothane anaesthesia was associated with significant reflex tachycardia in response to SNP induced hypotension. Eight patients in the halothane group (66%) requi red propranolol 0.5-3 mg to control tachycardia. Propofol anaesthesia attenuated significantly the reflex tachycardia in response to SNP ind uced hypotension. Two patients in the propofol group (16%) required 0. 5 mg propranolol to control reflex tachycardia. The mean SNP dose requ irements were 7.25 +/- 1.6 and 2.1 +/- 1.4 mug. kg-1.min-1 in the halo thane and propofol groups, respectively (P < 0.0001). None of the pati ents in the two groups developed rebound hypertension following SNP wi thdrawal. It is concluded that propofol anaesthesia reduces significan tly the dose requirements for SNP through attenuation of the homeostat ic reflex increase in the heart rate and systemic vascular resistance.