Comparison of nitroprusside, nitroglycerin, and deep isoflurane anesthesia for induced hypotension

Three methods of inducing hypotension were studied for their effects on the cardiovascular system and intrapulmonary shunting. Thirty patients were anesthetized with isoflurane in 70% N2O to a total of 1.25 to 1.3 MAC. Patients were divided into three groups of 10 each on the basis of the drug used to induce hypotension; sodium nitroprusside (SNP), nitroglycerin (NTG), or deep isoflurane anesthesia (ISF). Cardiac index was significantly decreased by NTG and ISF at a mean arterial blood pressure of 40 mm Hg compared to SNP (P less than 0.05). Systemic vascular resistance was decreased in all groups. Mixed venous oxygen content was significantly decreased from control in the NTG and ISF groups. There was no difference between the groups in arterial and mixed venous O2 content. Intrapulmonary shunting decreased with induction and, in the NTG and SNP groups, increased slightly but not significantly with induction of hypotension. Our data do not show a clear superiority of any agent over the other to induce hypotension, although SNP and perhaps ISF appear to be better than NTG to induce hypotension.