The effect of electrocortical state on cerebral carbohydrate metabolism in fetal sheep

We measured hemispherical cerebral blood flow and arteriovenous differences across the cerebral cortex for glucose, oxygen, and lactate during the two primary electroencephalographic patterns (high and low voltage) in unanesthetized, near-term fetal sheep. Oxygen consumption was 127 μmol/min/100 g brain in high voltage and was 14% higher in low voltage. Glucose uptake was 19 μmol/min/100 g and was 37% higher in low voltage. Cerebral blood flow was 112 ml/min/100 g and was 29% higher in low voltage. The glucose:oxygen quotient increased from 0.91 in high voltage to 1.08 in low voltage. There was a net lactate efflux of 3.2 μmol/min/100 g during low voltage compared to a net influx of 3.3 μmol/min/100 g in high voltage. During high voltage the fetal brain uses a small amount of lactate for oxidative metabolism. During low voltage, glucose uptake exceeds the oxygen uptake needed for completely aerobic consumption, and a portion of the energy utilized by the brain is produced anaerobically.