Review of sleep-EEG in preterm and term neonates

Abstract

Neonatal sleep is a crucial state that involves endogenous driven brain activity, important for neuronal survival and guidance of brain networks. Sequential EEG-sleep analysis in preterm infants provides insights into functional brain integrity and can document deviations of the biologically pre-programmed process of sleep ontogenesis during the neonatal period. Visual assessment of neonatal sleep-EEG, with integration of both cerebral and non-cerebral measures to better define neonatal state, is still considered the gold standard. Electrographic patterns evolve over time and are gradually time locked with behavioural characteristics which allow classification of quiet sleep and active sleep periods during the last 10weeks of gestation. Near term age, the neonate expresses a short ultradian sleep cycle, with two distinct active and quiet sleep, as well as brief periods of transitional or indeterminate sleep. Qualitative assessment of neonatal sleep is however challenged by biological and environmental variables that influence the expression of EEG-sleep patterns and sleep organization. Developing normative EEG-sleep data with the aid of automated analytic methods, can further improve our understanding of extra-uterine brain development and state organization under stressful or pathological conditions. Based on those developmental biomarkers of normal and abnormal brain function, research can be conducted to support and optimise sleep in the NICU, with the ultimate goal to improve therapeutic interventions and neurodevelopmental outcome.

Keywords: Brain maturation; EEG-monitoring; Preterm neonate; Sleep ontogenesis; Sleep-wake cycle.

Fig. 1. Preterm neonate (25 2/7 weeks GA), recorded at 25 3/7 PMA

a. Rudimentary state differentiation with more continuous and discontinuous EEG. High voltage central (red arrow) and temporal delta activity during more continuous EEG, lasting 20 s. b. Period of high discontinuity, with long IBIs alternated with high amplitude burst activity. Fluctuation of rudimentary state can also be observed in the aEEG trends (red arrow). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. Preterm neonate (26 3/7 weeks GA), recorded at 30 2/7 weeks PMA.

a. Continuous EEG activity associated with REM (red arrow). b. Discontinuous EEG (tracé discontinu) during QS, no REM and more regular breathing (red arrow). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3. Preterm neonate (30 4/7 weeks GA), recorded at 32 3/7 weeks PMA.

a. Continuous tracing during AS. Delta waves with superimposed fast rhythms (delta brushes) in both temporal and occipital brain regions. Irregular breathing pattern. Sleep state organization is now clearly visible in the aEEG trend. b. Preterm neonate (30 4/7 weeks GA), recorded at 32 3/7 weeks PMA. Discontinuous tracing during QS, with IBI's ≤ 15 s. More regular breathing pattern. Temporal theta activity mainly during QS and occipital delta brushes.

Fig. 4. Preterm neonate (29 4/7 weeks GA), recorded at 34 4/7 weeks PMA.

a. Continuous tracing during AS. Clear decrease in amplitude. Delta waves with superimposed fast rhythms (delta brushes) in the occipital brain regions (red circle). Immature frontal transient (symmetrical) (red arrow). Irregular breathing pattern. b. Tracé discontinu during QS, with IBI's ≤ 10s. More regular breathing pattern. Temporal theta decreased during QS and occipital delta brushes (red circle). Three periods of tracé discontinu can be observed in the aEEG trend. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5. Late term neonate (36 weeks GA), recorded at 38 6/7 weeks PMA.

Continuous activity with mixed frequencies during AS1 associated with REM, with higher amplitude and lower frequencies than during AS2. Frontal transients (red arrow) and slow anterior dysrhythmia in frontal regions (red line). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6. Preterm neonate (29 4/7 weeks GA), recorded at 36 3/7 weeks PMA.

Continuous tracing with low voltage irregular pattern during AS2 and REM (red arrow). EMG was omitted from this figure due to technical artefact. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 7. Late term neonate (36 weeks GA), recorded at 38 6/7 weeks PMA.

Tracé alternant activity during QS. Length bursts = length IBIs, IBI amplitude ≥ 25 μV (red line). Delta brushes only in QS (red circle) and rolandic theta (red line). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 8. Term neonate (41 2/7 weeks GA), recorded at 42 3/7 weeks PMA.

High voltage slow wave sleep at QS onset.