Combined general-epidural anesthesia decreases the desflurane requirement for equivalent A-line ARX index in colorectal surgery

Abstract

Background: The present study used the A-line ARX index, derived from auditory evoked potential measurements, to examine the effect of epidural lidocaine on the end-tidal concentration of desflurane during general anesthesia.

Methods: Thirty ASA I-II patients scheduled for elective colorectal surgery were included and randomized, in a double-blinded fashion, to receive general anesthesia, and 15 ml of either 2% lidocaine (group GE, n=15) or normal saline (group GS, n=15) was administered epidurally with a maintenance infusion rate of 6 ml h-1. After a 10-min high-flow oxygen wash-in period, desflurane was titrated to a target A-line ARX index (AAI) of 20+/-5.

Results: Epidural lidocaine reduced the end-tidal concentration of desflurane required to maintain an adequate clinical effect by 42% compared to general anesthesia alone (2.6% vs. 4.5%, respectively; P<0.001). The initial mean value of AAI was 87.8 (range 78-99) in group GE and 88.13 (79-99) in group GS before general anesthesia induction, the AAI values were approximately 19.7 (15-25) in group GE and 20.2 (16-25) in group GS during anesthesia maintenance, and returned to 84.53 (77-98) in group GE and 86.87 (79-98) in group GS when the patients regained consciousness in the recovery room. No statistical difference in the AAI values was observed either before, during, or after emergence of anesthesia. No patient reported intraoperative awareness.

Conclusions: Lower-than-expected concentrations of volatile anesthetics are sufficient to maintain appropriate a clinical anesthesia effect during combined general-epidural anesthesia under auditory-evoked potential monitoring.