Does Equi–Minimum Alveolar Concentration Value Ensure Equivalent Analgesic or Hypnotic Potency?

Abstract

BACKGROUND Minimum alveolar concentration (MAC) has traditionally been used to compare the potency of volatile anesthetics. However, as it reflects the spinal mechanism of immobility rather than the cerebral mechanism of analgesia and hypnosis, it is doubtful that equi-MAC connotes equivalent analgesic or hypnotic potency. The level of analgesia and hypnosis can be assessed using surgical pleth index and bispectral index (BIS) values, respectively. This study was designed to compare the surgical pleth index and BIS values produced by equi-MAC of desflurane and sevoflurane in patients undergoing single-agent volatile anesthesia. METHODS Eighty-nine patients were randomly allocated to two groups receiving either desflurane (n = 44) or sevoflurane (n = 45). Anesthesia was only maintained with assigned volatile anesthetic of age-corrected 1.0 MAC. Surgical pleth index values as an analgesic estimate and BIS values as a hypnotic estimate were obtained under standard tetanic stimulation. RESULTS Post-stimulation surgical pleth index values (mean ± SD), the primary outcome, were significantly lower for the desflurane group than those for the sevoflurane group (49 ± 10 vs. 64 ± 14, difference, 15 [95% CI, 10 to 20], P < 0.001). The desflurane group showed significantly lower poststimulation BIS values (median [interquartile range]) than the sevoflurane group (36 [31 to 41] vs. 41 [38 to 47], difference, 6 [95% CI, 2 to 9], P = 0.001). CONCLUSIONS During a steady-state of 1.0 MAC, desflurane and sevoflurane did not cause similar surgical pleth index and BIS values under the standardized nociceptive stimulus. These findings suggest that equi-MAC of desflurane and sevoflurane may not ensure equivalent analgesic or hypnotic potency.