The effects of sodium nitroprusside on cerebral blood flow and cerebral venous blood gases

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Abstract
Cerebral blood flow (CBF) and cerebral venous blood gases were investigated in 7 awake patients during hypotension induced with sodium nitroprusside. Infusion of the drug into the internal carotid artery produced no changes in cerebral hemodynamics. I.v. nitroprusside infusion resulted in a decrease in both CBF and jugular venous PO2 [partial pressure of O2] (P < 0.01, respectively). Reducing mean arterial blood pressure 18 and 43% produced a mean CBF fall of 6 and 27% respectively. Arteriovenous O2 difference increased in consonance with the CBF decrease (P < 0.01). Arterial PCO2 [partial pressure of CO2] fell during the infusion (P < 0.01). At 18% blood pressure reduction, the observed PCO2 decrease of 0.25 kPa could account for the 6% CBF decrease. At 43% blood pressure reduction, PCO2 fell by 0.53 kPa, a decrease which could not explain the observed CBF fall of 27%. Dizziness and incipient fainting occurred in the patients at this point. Apparently sodium nitroprusside has a minor but significant effect on cerebral hemodynamics in normal awake men.