The Effects of Profound Hypocapnia and Dilutional Anemia on Canine Cerebral Metabolism and Blood Flow

The effects of hypocapnia and dilutional anemia on cerebral metabolism and circulation were examined in 20 anesthetized dogs. In ten dogs, a reduction in Paco2 to 11 mm Hg did not alter the cerebral oxygen consumption rate (CMRo2), but with subsequent dilution of hemoglobin to 5 gm/100 ml of blood, a significant decrease in CMRo2 was observed. In ten other dogs, anemia alone did not alter CMRo2 bat with the addition of hypocapnia, a reduction in CMRo2 similar to that of the first group was observed. An increase in cerebral glucose consumption rate and a decrease in die oxygen–glucose index were observed in both groups of dogs prior to changes in CMRo2. Changes in cerebral blood flow and cerebrovascular resistance (CVR) due to hypocapnia alone or hemodilution alone were of the expected directions and magnitudes. However, in dogs hyperventilated after hemodilution, no change in CAR occurred. In these dogs, the reduction in CMRo2 that occurred was secondary to a reduction in O. extraction from the blood.