Abstract 1314 Poster Session IV, Tuesday, 5/4 (poster 242)

With the increasing survival of extremely premature infants, the need for early, simple and reliable tools to establish neurological prognosis evaluation is becoming crucial. Characteristics and usefulness of EEG are well assessed in mature newborns. The aim of this study is to define reference criteria for EEG in very premature infants.

Methods: the neonatal EEGs of 17 neurologically normal preterm infants, < 28 weeks gestational age (GA) have been analyzed. EEGs have been recorded during 40 to 60 minutes, on day 3, 7 and 15 to 21 with the conventional method. Normality of the infants was defined as the absence of any clinical abnormality within the neonatal period, normal head ultrasounds, and normal neurological outcome at 2 years of age or more. The analysis assessed continuity (i.e. duration of bursts with an amplitude ≥30µv), discontinuity (i.e. duration of interburst intervals), EEG patterns (α, β, δ, θ rhythms and other transients), temporal and spatial organization as well as sleep-wake differentiation.

Results: all tracings show discontinuities lasting up to 46 sec. Bursts are usually synchronous, lasting up to 3 minutes. EEG patterns consist mainly of δ waves (≤ 2 Hz), with high amplitude (up to 300µv) and occipital predominance. Other rhythms occur in short bursts: α, β, θ, intermixed with the δ waves. High rhythmic θ waves predominate on temporal areas, β waves are mainly rolandic, α waves are rolandic and occipital, reflecting spatial organization. These different rhythms are often organized in "spindle-shaped" bursts: the amplitude of the waves slightly increasing then decreasing during the burst. Sporadic multifocal sharp waves and frontal sharp transients may be observed. Variations in the continuity are related to the onset of clinical sleep differentiation. Some EEGs show patterns more mature than expected for the actual GA.

Conclusion: in premature infants < 28 weeks GA, EEG is a useful tool with constant reference patterns in normal infants. The different rhythms occur in characteristic "spindle-shaped" bursts. Discontinuous intervals up to 46 sec are normally observed. Patterns more mature than expected for GA suggest a progressing maturation. Further studies are needed to delineate the limits between these physiologic tracings and the appearance of other patterns, in addition to the well-known positive rolandic sharp waves, recorded in infants presenting neurological abnormalities.