Increased cerebral blood flow and plasma epinephrine in hypoglycemic, preterm neonates

Cerebral blood flow, plasma epinephrine, and plasma norepinephrine were measured in 25 spontaneously breathing, preterm neonates (mean gestational age 30.4 weeks) 2 hours after birth, during a routine screening for low blood glucose levels. Increased cerebral blood flow and plasma epinephrine values were observed when blood glucose levels were low, whereas plasma norepinephrine was constant throughout the blood glucose range. Hypoglycemia (defined as blood glucose concentration less than 30 mg/dL) was found in 13 neonates who were treated with intravenous glucose and milk enterally. Blood glucose levels were normal in the remaining 12 control neonates who received milk by a gastric line. Approximately 30 minutes after treatment with intravenous glucose and/or milk, cerebral blood flow had decreased by a mean of 11.3% in the 13 hypoglycemic neonates but was still 37.5% higher than cerebral blood flow in the control neonates despite normalization of plasma epinephrine concentration. Mean arterial blood pressure and blood gas values were identical between groups throughout the investigation. It is suggested that a normal coupling between cerebral metabolic demands and flow is present in very preterm neonates and that epinephrine may play a role in the cerebral hyperperfusion. Although none of the neonates had clinical signs of hypoglycemia, the data suggest that counterregulatory mechanisms are invoked when blood glucose values are less than 30 to 45 mg/dL.