OBJECTIVE: To evaluate the sparing effects of fentanyl and maropitant on sevoflurane minimum alveolar concentrations that block autonomic responses (MACBAR) and the hemodynamic and electroencephalographic responses to noxious stimuli in dogs. METHODS: The sevoflurane MACBAR was determined in 5 healthy male Beagles with or without continuous infusions of fentanyl and maropitant. Then, intermittent noxious stimulation was applied at 1.3, 1.0, and 0.7 MACBAR. Heart rate (HR), mean arterial pressure (MAP), and Patient State Index (PSI) were measured for 6 minutes before and during 6 minutes of stimulation and analyzed with generalized linear mixed-effects models. Patient State Index occurrences above 50 during stimulation were noted. The effective dose for burst suppression was determined. RESULTS: The baseline MACBAR was 2.26% (1.34, 3.19). No MACBAR-sparing effect of fentanyl and maropitant was observed. At 1.3 MACBAR, MAP, HR, and PSI were 50 (41, 91) mm Hg, 90 (64, 112) beats/min, and 2 (0, 44). Mean arterial pressure and PSI increased, but not HR, with lower MACBAR multiples (P <
.001). Noxious stimulation did not alter HR or PSI but elevated MAP. No PSI above 50 occurred at 1.3 MACBAR
however, 2 and 3 dogs showed brief PSI increases at 1.0 and 0.7 MACBAR. The effective dose for burst suppression was 3.15% (2.75, 3.75). CONCLUSIONS: Fentanyl and maropitant showed no MACBAR-sparing effect. At higher sevoflurane concentrations, noxious stimuli triggered an autonomic response
however, burst suppression was observed in the electroencephalogram. CLINICAL RELEVANCE: Variations in HR and MAP are unreliable indicators of anesthetic depth measured by electroencephalogram.