Maintenance of unconsciousness with low plasma propofol concentrations in the neohepatic phase of liver transplantation using bispectral index-guided propofol anesthesia: a case report.

The authors present a case where a drug-effect parameter, the bispectral index, was used to guide propofol infusion when propofol-remifentanil anesthesia was used for liver transplantation. The target concentration of remifentanil was kept constant throughout the operation, and the bispectral index indicated that propofol infusion was not required during the anhepatic and neohepatic phases of the operation. The measured plasma propofol concentrations during the neohepatic phase were far below the usual values that are used to maintain anesthesia. However, the bispectral index indicated a state of unconsciousness. The patient regained consciousness rapidly several minutes after administration of neostigmine and cessation of remifentanil infusion. The measured plasma propofol concentrations were similar before and after recovery of consciousness. The possible mechanisms for the maintenance of anesthesia at reduced propofol concentrations are multifactorial and may be related to reduced liver function as well as an interaction between propofol and remifentanil or the use of a neuromuscular relaxant to suppress somatic afferent activity.