Cerebral metabolism in the newborn lamb with polycythemia

Infants with polycythemia and hyperviscosity are known to have a reduced cerebral blood flow. Eight newborn lambs were studied to determine what effect the reduction in cerebral blood flow might have on the cerebral delivery and uptake of oxygen, glucose, lactate, pyruvate, beta-hydroxybutyrate, and acetoacetate. Measurements of cerebral blood flow, hematocrit, blood viscosity as well as delivery and uptake of the forementioned substrates were made during a control period and at 60, 180, and 300 min after an exchange transfusion with packed newborn red blood cells was performed to increase the hematocrit. Sixty min after the exchange transfusion, cerebral blood flow fell while cerebral oxygen delivery and uptake were stable. Although arterial glucose concentration remained unchanged, there was a significant fall in cerebral glucose delivery. At 180 min after the exchange transfusion, the arterial glucose concentration fell from 90 to 70 mg/100 ml causing the cerebral glucose delivery to further decrease. This resulted in a significant fall in the cerebral glucose uptake and glucose:oxygen quotient. At 300 min arterial glucose concentration remained low but a rise in cerebral blood flow resulted in a small increase in the cerebral glucose delivery and consequently the cerebral glucose uptake and glucose:oxygen quotient returned to normal. We conclude that polycythemia results in a decrease in cerebral glucose delivery and uptake during normoglycemia.