Changes in anterior fontanel pressure in preterm neonates receiving isoflurane, halothane, fentanyl, or ketamine

The effects of anesthetics on intracranial pressure (ICP) may be different in preterm neonates than in adults because the neonate's cranial sutures are not yet fused. The authors monitored changes in anterior fontanel pressure (AFP), a noninvasive indicator of ICP, during anesthesia in 44 preterm neonates without neurologic disease. Atropine, 0.02 mg/kg, and pancuronium, 0.1 mg/kg, were given intravenously to all patients, who were ventilated with oxygen and air. Anterior fontanel pressure was monitored and recorded continuously with a Ladd AFP monitor. Systolic blood pressure (SAP) and mean blood pressure (MAP) were recorded at 1-min intervals. After a 5-min control period of stable AFP, each of the four groups of 11 patients then received either 0.75% isoflurane, 0.5% halothane, 20 micrograms/kg fentanyl, or 2 mg/kg ketamine. Anterior fontanel pressure decreased 11% during isoflurane administration, 9% during halothane administration, 10% after fentanyl, and 10% after ketamine. These changes were statistically significant, but clinically mild, and AFP remained within the normal range. Statistically significant decreases in SAP and MAP occurred during isoflurane and halothane administration, but not after fentanyl or ketamine. The authors conclude that indirectly measured ICP decreases slightly in preterm neonates without neurologic disease after administration of the anesthetics studied. The difference between these results and those of studies of ICP in adults is presumably due to the compliance of the neonate's open-sutured cranium.