The aim of this study is to evaluate the cardiopulmonary and acid-base effects of continuous rate infusion of butorphanol in isoflurane anesthetized horses breathing spontaneously. Six adults equines will be used distributed in two groups GB (butorphanol group) and GC (control group), being respected a minimum interval of 7 days among the protocols. The animals will receive from preanesthetic medication xylazine (0.5mg/kg IV) and 10 minutes after, ketamine (1.5mg/kg IV) associated to midazolam (0.1mg/kg IV). Immediately after, the equines will be intubated and submitted to anesthesia by the administration of isoflurane, diluted in O2. After 30 minutes, the animals from GB will received, butorphanol (0.05 mg/kg IV) and immediately after continuous rate infusion of butorphanol, at the dose of 13 mcg/kg/h. In GC the same methodology will be adopted, being substituted the opioid by the saline solution at 0.9%. The variables HR, SAP, DAP, MAP, RR, ETCO2, SpO2, PaO2, PAO2, PaCO2, SaO2, HCO3, BE, pHa and Temperature will be measured immediately before the application of the opioid or saline solution at 0.9% (M0). New measurements will be accomplished 15 minutes after the continuous rate infusion of butorphanol or saline (M15) and the other measurements will be carried out at 15 minutes intervals, for a period of 60 minutes M30, M45, M60 and M75, respectively. All the numeric data will be evaluated by analysis of variance for repeated measures (ANOVA), followed by the Tukey test (p<0.05).
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