Neonatal electroencephalography shows low sensitivity to anesthesia.

This study examined EEG under clinical anesthesia in neonates and infants, to clarify how growth affects EEG during anesthesia. Subjects comprised 62 neonates and infants. Patients were divided into four groups according to age: Group 1 (neonates), <1 month; Group 2, 1-2 months; Group 3, 3-5 months; and Group 4, 6 months to 2 years. Anesthesia was maintained with sevoflurane and fentanyl and/or caudal block. At four points of sevoflurane concentration (0.5%, 1%, 1.5%, and 2%), 90% spectral edge frequency (SEF90), burst suppression ratio (BSR), relative beta ratio (RBR) and approximate entropy (ApEn) were analyzed. In Group 4, SEF90, BSR, RBR and ApEn changes were dependent on the concentration of anesthesia, along with changes in sevoflurane concentration from 0.5% to 2% (from 14.3 (2.7) [mean (SD)] Hz to 8.2 (3.8) Hz, from 0.0 to 0.32 (0.36), from -1.58 (0.14) to -1.10 (0.15), and from 0.56 (0.25) to 0.24 (0.25) respectively; p<0.05 each). Conversely, these processed EEG parameters in Group 1 showed little anesthesia-dependent change under sevoflurane concentrations between 0.5% and 2% (SEF90: 7.3 (1.2) Hz vs. 7.7 (2.1) Hz; BSR: 0.51 (0.20) vs. 0.62 (0.29); RBR: -1.00 (0.17) vs. -1.03 (0.27); ApEn: 0.32 (0.18) vs. 0.25 (0.14), respectively). The unique EEG features of neonates during anesthesia rapidly change to the usual anesthesia-dependent patterns seen in older children, with a boundary of 3-5 months old. In infants younger than 6 months old, neural network regulation reflected in EEG by anesthesia is weak.