EEG patterns in 10 extreme premature neonates with normal neurological outcome: qualitative and quantitative data

The aim of this prospective study was to describe and quantify EEG patterns in 10 very premature infants (24 weeks 2 days– 26 weeks 4 days GA) without neonatal neurological pathology and with a normal outcome at 3 years of age for nine of them. EEG and eye movements were recorded in the first 5 days of life. All tracings were discontinuous; EEG inactivity (<15 μV) never exceeded 1 min, representing 45.3% of total recording time. The EEG bursts, mainly synchronous, could last up to 83 s when >50 μV and to 197 s when >15 μV. High voltage delta waves (0.5 Hz; up to 330 μV), either smooth or superimposed with 7–12 Hz rhythms, were the most typical and frequent figures, mainly in temporal (mean number 257.2±73.3) and occipital (237.7±65.8 per hour recording) areas. In temporal areas, they appeared mainly in clusters; more often unilateral than bilateral (P<0.05). Occipital delta waves were as often bilateral and synchronous as unilateral. The two distinct frontal delta waves were significantly less numerous than other delta waves (P<0.05). Bursts of hypersynchronous high voltage delta waves and of diffuse sharp theta waves were less numerous than other waves (P<0.01). Considering periods with or without eye movements, the mean percentage and the mean longest period of EEG activity (≤50 μV) were significantly greater (P<0.01) when eye movements were present, indicating a rough sleep state differentiation as early as 25 weeks CA. These EEG patterns are qualitatively and quantitatively reproducible. They constitute standards of normality and a basis for the determination of neurological prognosis.