Sevoflurane Sparing Effect of Morphine in Tegus (Salvator merianae) – A Preliminary Study

Abstract

This study aimed to determine the minimum anesthetic concentration (MAC) of sevoflurane in tegus (Salvator merianae) and the morphine-sparing effect on this variable. In a prospective, non-blinded, crossover study, MAC was first determined in 6 tegus under sevoflurane anesthesia alone (MACSEVO) and then following intramuscular administration of morphine (10 mg/kg), administered 3 hour before sevoflurane anesthesia (MACSEVO+MOR). A standard bracketing technique was applied to determine the MAC by an electrical supramaximal noxious stimulus (50 Hz, 30 mA) delivered at the base of the tail of the tegus. The end-tidal sevoflurane fraction was reduced or increased by 10% in any evidence of negative or positive motor responses, respectively. The MAC was calculated as the mean of the 2 highest successive sevoflurane concentrations that permitted positive responses and the 2 lowest that prevented positive responses. Heart rate, esophageal temperature, and noninvasive mean arterial blood pressure were assessed every 10 minutes. The MAC was significantly different between MACSEVO (2.41 ± 0.06%) and MACSEVO+MORF (1.88 ± 0.43%) (P = .007), with a mean ± SD morphine-induced reduction in the sevoflurane MAC of 22 ± 18% (P = .0158). Heart rate, mean arterial blood pressure, and esophageal temperature did not differ between groups or within groups over time. Results showed that intramuscular premedication with 10 mg/kg morphine produced a sevoflurane sparing effect in tegus with no significant impact on cardiovascular variables.