Rectal temperature changes during sleep state transitions in term and preterm neonates at postconceptional term ages

Mean rectal temperatures in neonates were investigated during sleep state transitions as assessed by visually analyzed electroencephalographic-polygraphic recordings. Continuous 3-hour studies were obtained on 3 term and 5 preterm infants at postconceptional term ages using a 24-channel computerized monitoring system. In the study, 1,461 min were assigned an EEG state by traditional criteria. Mean rectal temperature measurements were tabulated for each minute of sleep. Data were analyzed both as 1,461 consecutive minutes of sleep, and as 28 complete ultradian neonatal sleep cycles. Exploratory analyses were performed using t tests, Mann-Whitney U tests, and one-way analysis of variance. Decreases in mean rectal temperatures followed a transition from active to quiet sleep for only the term group. The preterm group had higher temperatures at sleep onset than the term group and demonstrated no changes during state transitions. Higher temperatures were maintained in the preterm group during both active and quiet sleep (i.e., 36.7 degrees C versus 36.4 degrees C, P = .02) when 28 complete cycles of sleep were compared and during the transition when 658 min of active sleep were compared to 617 min of quiet sleep. These findings are preliminary; however, the phenomenon of state-dependent changes in mean rectal temperature in neonates based on electroencephalographic sleep is unreported. Higher mean rectal temperatures during active sleep and altered temperature responses during transition to quiet sleep in the preterm infant suggest altered brain function because of the preterm infant's adaptation to the extrauterine experience.