Cardiovascular effects of sodium nitroprusside in cerebral aneurysm surgery

Cardiovascular effects of sodium nitroprusside (SNP) were studied in 17 patients undergoing cerebral aneurysm surgery under controlled hypotension. In 10 patients oxygen uptake was also calculated. Mean arterial blood pressure was decreased from 91 to 58 mmHg by SNP due to reductions in both total peripheral resistance (29%) and cardiac output (15%). Mean right atrial and pulmonary capillary wedge pressures were reduced during hypotension. Total oxygen uptake remained constant throughout the procedure. There was no significant change in arterial oxygen tension in the hypotensive period, but after discontinuation of SNP infusion it was significantly increased. The haemodynamic effects of SNP in patients with a recent subarachnoid haemorrhage and its effect on blood oxygenation are discussed. It is concluded that the fall in cardiac output is related to a reduction of central blood volume and might be more pronounced in these patients than in normal subjects.