Isoflurane MAC determination in dogs using three intensities of constant-current electrical stimulation

ObjectivesTo compare isoflurane minimum alveolar concentrations (MACs) in dogs determined using three intensities of constant-current electrical stimulation applied at the tail, and thoracic and pelvic limbs, and to compare isoflurane MACs obtained with all combinations of electrical stimulation and anatomic site with those obtained using the tail clamp as the noxious stimulus. Study designRandomized trial. AnimalsSix mixed-breed, adult female dogs aged 1-2years and weighing 11.14.4kg. MethodsIn each dog, MAC was determined by thebracketing method with the tail clamp (MAC(TAILCLAMP)), and three electrical currents (10mA, 30mA, 50mA) at three anatomic sites (thoracic limb, pelvic limb, tail). Each MAC achieved with electrical stimulation was compared with MAC(TAILCLAMP) using a mixed-model anova and Dunnett's procedure for multiple comparisons. The effects of current intensity and anatomic site on isoflurane MAC were tested using a mixed-model anova followed by Tukey's test for multiple comparisons (p<0.05). ResultsMean MAC(TAILCLAMP) was 1.69%. MACs achieved with currents of 30mA and 50mA did not differ independently of anatomic site. When currents of 10mA were applied to the tail and thoracic limb, resulting MACs were lower than those obtained using currents of 30mA and 50mA. Currents of 30mA and 50mA provided MACs that did not differ from those of MAC(TAILCLAMP), whereas a current of 10mA achieved the same result only for the pelvic limb. Conclusions and clinical relevanceIsoflurane MAC is affected by current intensity and anatomic site. Current intensities of 30mA and 50mA provided consistent results when applied to the tail, and thoracic and pelvic limbs that did not differ from those obtained using the tail clamp. Consequently, they can be used in place of the tail clamp in MAC studies in dogs.