• Tak Kyu Oh, Woosik Eom, Jiyeon Yim, Namwoo Kim, Kyungho Kwon, Seong-Eun Kim, and Dae Hyun Kim.
• From the *Department of Anesthesiology and Pain Medicine, National Cancer Center, Gyeonggi-do, Republic of Korea; †Department of Anesthesiology and Pain Medicine, Moonsan Central General Hospital, Gyeonggi-do, Republic of Korea; and ‡Department of Biostatistics, Korea University College of Medicine, Seongbuk-gu, Republic of Korea.
• Anesth. Analg. 2017 Jul 1; 125 (1): 156-161.

BackgroundOpioid analgesics decrease the minimum alveolar concentration of inhalation agents during the acute phase response. However, the effect of chronic opioid exposure on minimum alveolar concentration of inhalation agents remains unknown. This study aimed to determine the concentration of sevoflurane necessary to maintain a bispectral index (BIS) <50 (SEVOBIS50) in patients with chronic opioid use compared with those naïve to opioid use.MethodsWe included chronic opioid users who received a stable dose of oral morphine of at least 60 mg/d according to the morphine equivalent daily dose for at least 4 weeks and opioid-naïve patients. General anesthesia that included thiopental, vecuronium, and sevoflurane in oxygen was administered to all patients. Anesthesia was maintained using predetermined end-tidal sevoflurane concentrations. Fifteen minutes after achieving the determined end-tidal sevoflurane concentration through closed circuit anesthesia, BIS was measured for 1 minute in both groups. SEVOBIS50 was determined using Dixon's up-down method and probit analysis.ResultsNineteen and 18 patients from the chronic opioid and control groups, respectively, were included in the final analysis. SEVOBIS50values for the chronic opioid and control patients were 0.84 (95% confidence interval, 0.58-1.11) and 1.18 (95% confidence interval, 0.96-1.40), respectively (P = .0346).ConclusionsOur results suggest that the end-tidal concentration of sevoflurane necessary to maintain a BIS <50 is lower for chronic opioid users than for opioid-naïve patients.

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