Monitoring of anesthetic depth is important for successful general anesthesia, yet no such a monitor is widespread. Recently, anesthesia-monitoring device based on time-frequency balanced spectral entropy of electroencephalogram monitoring was developed and available in clinical practices. This study was performed to evaluate the effectiveness of this monitor on the consumption of anesthetic drugs and recovery time in general inhalational anesthesia.

Patients scheduled for elective operation under inhalational anesthesia were randomly allocated to entropy (E) group (with entropy monitoring) or non-entropy (NE) group (without entropy monitoring). Anesthesia was maintained with sevoflurane, air, and remifentanil in all patients. In E group, the concentration of sevoflurane was adjusted to keep the state entropy (SE) value between 40 and 60. The concentration of sevoflurane in NE group was controlled to keep heart rate and blood pressure within ± 20% of the baseline value without the information of SE. After the operation, entropy values, end-tidal sevoflurane concentration, and recovery time were compared with each other.

A total of 60 patients were studied. Entropy values were higher during anesthesia period in the E group (P < 0.05). Consequently, mean end-tidal sevoflurane concentration was lower in the E group during anesthesia period (P < 0.05). And all recovery time was shorter in the E group (P < 0.05).

Entropy monitoring assisted titration of sevoflurane, as indicated by higher entropy values, decreased mean end-tidal sevoflurane concentration, and shorter recovery times in the entropy group.