The relationship between bispectral index and endtidal concentration of sevoflurane during anesthesia and recovery in spontaneously ventilating children

Abstract

Background: Global inverse correlation between BIS (bispectral index) and depth of anesthesia using sevoflurane has been documented in children in several studies under experimental conditions and in steady-state conditions during mechanically controlled ventilation. Because sevoflurane mask anesthesia combined with a peripheral nerve block is widely used in children, we studied the relationship between BIS and endtidal concentration of sevoflurane (PE(sevo)) under these conditions during surgery and emergence.

Methods: In this prospective blinded study of 32 children, the relationship between BIS and PE(sevo) was studied during sevoflurane anesthesia via facemask combined with peripheral nerve block. The intraoperative phase was studied during steady-state conditions (fixed PE(sevo)) and the emergence phase was studied during fast alveolar washout (FAW). BIS and PE(sevo) data fitted using the E(max) model. Coefficients of variation of BIS and PE(sevo) during the two periods were compared.

Results: Fit was adequate with the simple E(max) model. Intraoperative variation in BIS was large (28.4%), and larger than at awakening (28.4% vs 8%). At awakening, BIS varied less than PE(sevo) (8% vs 28.5%). No difference was found between children younger and those older than 5 years.

Conclusions: Caution is required for intraoperative titration based on BIS when spontaneous ventilation is maintained because of the wide variability compared with PE(sevo). During emergence using FAW, BIS varied significantly less than PE(sevo), but the clinical relevance of this point could be discussed during anesthesia without tracheal intubation.