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.
The dose of volatile anesthetic agents is measured in minimum alveolar concentration (MAC) multiples. MAC, however, is a reflection of the activity of volatile agents on the spinal cord and it is not clear whether equi-MAC doses of volatile agents result in equivalent analgesia and hypnosis.
In patients anesthetized with 1.0 minimum alveolar concentration of either desflurane or sevoflurane, analgesic and hypnotic potency, as measured by surgical pleth index and bispectral index, were greater with desflurane than with sevoflurane.
The results suggest that volatile agent equivalence of effect at the spinal cord is not equivalent to the effect at the brain, when evaluated by analgesia and hypnosis.