Cardiorespiratory effects of induction and maintenance of anesthesia with ketamine-midazolam combination, with and without prior administration of butorphanol or oxymorphone

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Summary Cardiorespiratory effects of an iv administered bolus of ketamine (7.5 mg/kg of body weight) and midazolam (0.375 mg/kg) followed by iv infusion of ketamine (200 μg/kg/min) and midazolam (10 μg/kg/min) for 60 minutes was determined in 6 dogs. Ketamine-midazolam combination was administered to dogs on 3 occasions to determine effects of prior administration of iv administered saline solution (1 ml), butorphanol (0.2 mg/kg), or oxymorphone (0.1 mg/kg). The infusion rate of ketamine and midazolam was decreased by 25% for anesthetic maintenance after opioid administration. There were no significant differences in cardiorespiratory variables after saline solution or butorphanol administration; however, oxymorphone caused significant (P < 0.05) increases in mean arterial blood pressure, systemic vascular resistance, and breathing rate. Bolus administration of ketamine-midazolam combination after saline solution caused significant (P < 0.05) increases in heart rate, mean arterial blood pressure, cardiac index, mean pulmonary blood pressure, venous admixture, and significant decreases in stroke index, pulmonary capillary wedge pressure, arterial and mixed venous oxygen tension, arterial oxygen content, and alveolar-arterial oxygen gradient. Opioid administration was associated with significantly (P < 0.05) lower values than was saline administration for heart rate, mean arterial blood pressure, and arterial and mixed venous pH and with higher values for stroke index, pulmonary capillary wedge pressure, and arterial and mixed venous carbon dioxide tension. Prior oxymorphone administration resulted in the highest (P < 0.05) values for mean pulmonary blood pressure, venous admixture, and arterial and mixed venous carbon dioxide tension, and the lowest values for arterial oxygen tension, and arterial and mixed venous pH. Each treatment provided otherwise uncomplicated anesthetic induction, maintenance, and recovery. Time to extubation, sternal recumbency, and walking with minimal ataxia was similar for each treatment.