Effects of Lidocaine, Dexmedetomidine or Their Combination on the Minimum Alveolar Concentration of Sevoflurane in Dogs

The aim of this study was to determine the effects of lidocaine (LIDO) and dexmedetomidine (DEX) or their combination (LIDO–DEX), administered by constant-rate infusion (CRI), on the minimum alveolar concentration (MAC) of sevoflurane in dogs. Seven healthy mongrel dogs were used with a 2-week washout interval between treatments in this study. Anesthesia was induced with propofol and maintained with sevoflurane in oxygen, and MAC of sevoflurane was determined after 90 min equilibration period in the dogs (SEV-MAC(BASAL)). Then, sevoflurane MAC was determined again in the dogs after 45 min equilibration period of one of the following treatments: an intravenous loading dose of lidocaine 2 mg/kg followed by 6 mg/kg/hr CRI (SEV-MAC(LIDO)); an intravenous loading dose of dexmedetomidine 2 µg/kg followed by 2 µg/kg/hr CRI (SEV-MAC(DEX)); or their combination (SEV-MAC(LIDO-DEX)). These SEV-MACs were determined in duplicate. Data were analyzed using ANOVA and post hoc Tuckey test when appropriate. The SEV-MAC(BASAL) was 1.82 ± 0.06%, SEV-MAC(LIDO) was 1.38 ± 0.08%, SEV-MAC(DEX) was 1.22 ± 0.10%, and SEV-MAC(LIDO-DEX) was 0.78 ± 0.06%. The CRI administration of lidocaine, dexmedetomidine and their combination produced a significant reduction in the MAC of sevoflurane by 26.1 ± 9.0% (P<0.0001), 43.7 ± 11.8% (P<0.0002) and 54.4 ± 9.8% (P<0.0001), respectively. The MAC reduction was significantly greater after the CRI combination of lidocaine and dexmedetomidine when compared with lidocaine CRI (P<0.0001) or dexmedetomidine CRI treatments (P<0.025).