Hemodynamic Effects of Medetomidine-Midazolam-Butorphanol and Medetomidine-Midazolam-Buprenorphine Combinations and Reversibility by Atipamezole in Dogs

OBJECTIVE--To characterize the hemodynamic effects of medetomidine (1 mg/m2 of body surface area; dosage, 39 to 46 micrograms/kg of body weight, IM) and midazolam (1 mg/kg of body weight, i.v.) combined with butorphanol (0.1 mg/kg, i.v.), buprenorphine (10 micrograms/kg, i.v.) or saline solution. Reversibility of these effects by atipamezole (2.5 mg/m2; dosage, 97.5 to 115 micrograms/kg, IM) was evaluated. DESIGN--2 treated groups and 1 control group, without repetition. ANIMALS--15 clinically normal dogs (3 groups of 5). PROCEDURE--Medetomidine was administered at time 0; midazolam and butorphanol, buprenorphine, or saline solution at time 20; and atipamezole at time 60. Heart rate, systemic and pulmonary arterial pressures, central venous pressure, body temperature, cardiac output, and arterial and mixed venous blood gas tensions and pH were measured. Cardiac index, stroke index, systemic and pulmonary vascular resistances, and left and right stroke work indexes were calculated. RESULTS--Body temperature, heart rate, cardiac index, and stroke index were significantly decrease below baseline values in some groups. Central venous pressure, pulmonary capillary wedge pressure, and systemic vascular resistance were significantly increased above baseline in all groups. Arterial and venous PO2 and pH decreased in all groups and PCO2 increased, but these changes were more pronounced when buprenorphine was administered. Arterial pressure decreased after atipamezole administration. CONCLUSION--The combinations seemed to result in cardiorespiratory depressant effects of similar importance and most of these effects, which are related to medetomidine, were reversed by atipamezole.