Quantitative sleep stage analyses as a window to neonatal neurologic function.

OBJECTIVE: To test the hypothesis that neonatal sleep physiology reflects cerebral dysfunction, we compared neurologic examination scores to the proportions of recorded sleep/wake states, sleep depth, and sleep fragmentation in critically ill neonates.
METHODS: Newborn infants (≥35 weeks gestation) who required intensive care and were at risk for seizures were monitored with 8- to 12-hour polysomnograms (PSGs). For each infant, the distribution of sleep-wake states, entropy of the sequence of state transitions, and delta power from the EEG portion of the PSG were quantified. Standardized neurologic examination (Thompson) scores were calculated.
RESULTS: Twenty-eight infants participated (mean gestational age 39.0 ± 1.6 weeks). An increased fraction of quiet sleep correlated with worse neurologic examination scores (Spearman rho = 0.54, p = 0.003), but the proportion of active sleep did not (p > 0.1). Higher state entropy corresponded to better examination scores (rho = -0.43, p = 0.023). Decreased delta power during quiet sleep, but not the power at other frequencies, was also associated with worse examination scores (rho = -0.48, p = 0.009). These findings retained significance after adjustment for gestational age or postmenstrual age at the time of the PSG. Sleep stage transition probabilities were also related to examination scores.
CONCLUSIONS: Among critically ill neonates at risk for CNS dysfunction, several features of recorded sleep-including analyses of sleep stages, depth, and fragmentation-showed associations with neurologic examination scores. Quantitative PSG analyses may add useful objective information to the traditional neurologic assessment of critically ill neonates.