Use of sodium nitroprusside in post-coronary bypass surgery. A plea for conservatism.

In 292 patients who underwent coronary artery bypass graft (CABG) surgery, seven patients developed sodium nitroprusside (SNP) toxicity in the postoperative period. Duration of infusion varied between 26 to 160 hrs and total SNP dose ranged from 1.8 to 12 mg/kg body weight. All patients were critically ill and required ventilatory support in the postoperative period. Tachyphylaxis to SNP requiring increase of SNP dose for control of hypertension, and loss of consciousness were the major signs of toxicity. Other commonly described signs of SNP toxicity were absent in those patients. Discontinuation of SNP therapy and treatment with sodium thiosulfate was followed by improvement in four patients. Three patients who failed to regain consciousness later died because of hemodynamic, pulmonary and/or renal complications. Our observation suggests that recommended doses of SNP may be toxic in unstable post-CABG patients. We recommend that the dose and duration of SNP infusion be minimized in critically ill patients.