BLOOD FLOW AND OXYGEN CONSUMPTION OF THE HUMAN BRAIN DURING ANESTHESIA PRODUCED BY THIOPENTAL

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Abstract
The investigations were carried out on 11 young females and 1 young male who, following premedication with demerol and scopolamine or morphine and atropine, were anesthetized with 0.5 to 1.6 g. of thiopental Na for minor surgical procedures. Bilateral internal jugular venapuncture was performed in 10 patients and unilateral in 2 patients. Cerebral blood flow was measured by the nitrous oxide method. Pulse rate and mean arterial blood pressure were recorded before and during each flow detn. Blood gas analyses were made with the Van Slyke-Niell apparatus. Blood pH was detd. anaerobically with a closed glass electrode and Cambridge potentiometer. Cerebral metabolic rate in terms of cerebral O2 consumption and cerebrovascular resistance were calculated by the method of Kety. Cerebral utilization of O2 was depressed from a normal of 3.3 to a mean of 2.1 ml. O2/100 g. of brain/min. The avg. cerebral arteriovenous O2 difference was lowered from a normal of 6.3 vol.% to 3.7 vol.%. Although the mean arterial blood pressure decreased from a normal of 85 mm. Hg to 71 mm. Hg, the cerebral blood flow increased from a normal of 54 to a mean of 61 ml./100 g. of brain/min. This latter can be explained by the fact that the cerebrovascular resistance, primarily a measure of cerebral vessel tone, was lowered from a normal mean of 1.6 units to 1.3 units. The lowered cerebrovascular resistance was probably due in part to the slight anemia found in these patients and to the vasodilatory effect of the increased CO2 tensions found in the arterial and internal jugular blood. Arterial O2 content was 10% lower than could be expected with complete hemoglobin saturation, which in conjunction with the CO2 retention indicates some degree of respiratory depression as expected from intraven. thiopental. The cerebral respiratory quotient was decreased from 1.00 to 0.89. The results of all bilateral measurements in the various patients were practically identical for each side, and it is therefore concluded that the venous blood of the cortical and subcortical areas mix adequately before entering the jugular veins.

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