Influence of changes in arterial pCO2 on cerebral blood flow and metabolism during high-dose barbiturate therapy in dogs

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Abstract
In 13 dogs, the response of the cerebral circulation to changes in PaCO2 [arterial partial pressure of CO2] ranging from 20-60 torr was studied before and after administration of high doses of sodium thiopental. Infusion of sufficient barbiturate to produce 30-60 s burst suppression in the EEG was associated with a profound degree of cerebral vasoconstriction, equivalent to that produced by hypocapnia with PaCO2 = 20 torr. Once sodium thiopental was administered, no significant difference in cerebral blood flow or vascular resistance (CVR) was noted between PaCO2 of 30 and 20 torr. Changes of approximately 15% in CBF and 30% in CVR were noted between PaCO2 at 40 and 20 torr. Hyperventilation of PaCO2 of < 30 torr may not effectively increase the degree of cerebral vasoconstriction in these circumstances.