The effect of phenobarbital on asphyxia in the newborn monkey.

This study characterizes the circulatory changes associated with asphyxia in the newborn monkey and examines the effect of phenobarbital on asphyxia. The time to last gasp and duration of total asphyxia as well as heart rate at the start of resuscitation were the same in the phenobarbital-treated and untreated infants. Initial cardiac output was the same in both groups; there was a profound drop in cardiac output with asphyxia which was the same in both groups. Organs which preferentially receive a greater percentage of cardiac output during asphyxia are heart, total brain, and adrenal glands. Organs receiving a decreased percentage of cardiac output during asphyxia are kidneys, liver, and gastrointestinal tract. Cerebral hemisphere flow as a percentage of cardiac output is maintained during asphyxia, whereas paleoencephalon flow as a percentage of cardiac output increases significantly. These data confirm the circulatory redistribution of cardiac output in response to asphyxia described previously in the monkey fetus. The treated infants did not show the prolongation of time to last gasp reported in the monkey fetus; the dose of phenobarbital we used, although adequate to produce sedation, may have been too low to demonstrate the protective effect.