The effects of sodium nitroprusside on cerebral blood flow and cerebral venous blood gases. I. Observations in awake man during and following moderate blood pressure reduction.

Cerebral blood flow (CBF) and cerebral venous blood gases were studied in seven patients before, during and after intravenous sodium nitroprusside infusion. The 133Xe intra-arterial injection method was used for the CBF measurements. A dose of sodium nitroprusside (mean 1.0 mg, mean infusion time 20 min), which reduced mean arterial blood pressure by a mean of 17%, resulted in a 13% decrease in CBF (P less than 0.05). Measurements obtained 5 and 20 min after termination of the sodium nitroprusside infusion showed no signs of a hyperaemic rebound effect. Arterial PCO2, metabolic rate of oxygen, arterio-venous oxygen difference and venous PO2 remained unchanged during and after infusion. It is concluded that sodium nitroprusside has a minor effect on cerebral haemodynamics, an effect that might be mediated by the sympathetic nervous system.