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

In 13 dogs the response of the cerebral circulation to changes in PaCO2 ranging from 20 to 60 torr was studied before and after administration of high doses of sodium thiopental. Infusion of sufficient barbiturate to produce 30- to 60-second burst suppression in the electroencephalogram was associated with a profound degree of cerebral vasoconstriction, equivalent to that produced by hypocapnia with PaCO2 = 20 torr. Furthermore, once sodium thiopental was administered, no significant difference in cerebral blood flow (CBF) or vascular resistance (CVR) was noted between PaCO2 of 30 and 20 torr. However, changes of approximately 15% in CBF and 30% in CVR were noted between PaCO2 at 40 and 20 torr. These data suggest that hyperventilation of PaCO2 of less than 30 torr may not effectively increase the degree of cerebral vasoconstriction in these circumstances.