Usefulness of permutation entropy as an anesthetic depth indicator in children

Permutation entropy (PE) as a complexity measure has been introduced to monitor anesthetic depth for adult. However, PE has not yet been evaluated for its clinical applicability as an indicator of anesthetic depth in children. Therefore, in order to investigate the validity of PE, we compared PE with BIS using pharmacodynamic (PD) modeling in children. Electroencephalogram (EEG) was obtained from BIS monitor during sevoflurane deepening and lightening protocol. End-tidal sevoflurane concentration (Etsevo) and BIS were measured simultaneously. PE was calculated from the processed EEG with the scale ranging from 0 to 100. NONMEM software was used to investigate the PD relationship between Etsevo with BIS and PE. Adjusted PE (APE) values were decreased as anesthesia deepened. APE and BIS showed significant linear correlation (P < 0.001), indicating that PE also reflects anesthesia depth. PD parameters for APE and BIS were estimated with a sigmoid Emax model which describes the relationship between Etsevo and APE/BIS (E (o) : 78, E (max) : 17.6, C (e50) : 2.5 vol%; gamma: 13.1, k (eo) : 0.47 min(-1) for APE; E (o) : 89.4; E (max) : 15.7; C (e50) : 2.2 vol%; gamma: 6.6, k(eo): 0.52 min(-1) for BIS). PE seems to be a useful indicator of anesthetic depth, which is comparable to BIS in children.