Normal EEG in very premature infants: reference criteria.

OBJECTIVES

Objectives were to precise EEG criteria of normality in very premature infants.

METHODS

The neonatal electroencephalograms (EEGs) of 17 neurologically normal very premature infants recorded at a conceptional age (CA) of 26-28 weeks have been analyzed. The normality of the infants was defined as normal neonatal cranial ultrasound scans and normal neurological outcome at a minimum postnatal age of 2 years.

RESULTS

All tracings were discontinuous. The bursts (amplitude >/=30 microV) were interhemispherically synchronous and lasted up to 3 min. The interburst intervals lasted up to 46 s. EEG patterns consisted mainly of slow waves (</=3 Hz), with high amplitude (up to 300 microV), occipital predominance and superimposed alpha, beta and theta rhythms. High amplitude theta rhythms predominated on temporal areas, beta rhythms were mainly central, whereas alpha rhythms were central and occipital. Sleep state differentiation began as early as 26 weeks CA. On a given trace, the existence of more mature graphoelements than expected for the CA reflected a normal increasing maturation.

CONCLUSIONS

EEG has constant and reproductible patterns in normal very premature infants. This can constitute a basis for the determination of EEG criteria for neurological prognosis in infants of 26-28 weeks CA.