Six young healthy mixed breed dogs of both sexes were used for this study. Following parameters were measured; arterial, central venous, and pulmonary arterial blood pressures; heart rates(HR); and cardiac output(CO). Immediately after baseline(BL) measurements(time 0), each dog received an IM injection of either a combination of medetomidine at 10mcg/kg and atropine at 0.04mg/kg(group MAA), or medetomidine at 10mcg/kg(group MA). Atipamezole at 50mcg/kg was administered IM one hour later(time 60; T60) to each dog. For comparison, the cardiopulmonary measurements were taken at 5 minute intervals for the first 20 minutes following each drug administration, then at 10 minute intervals for further 40 minutes, totaling to 120 minutes of entire measurement time.

HR decreased markedly in both groups at T5, but thereafter, in group MAA, markedly increased and then returned to BL by T60, whilst in group MA remained decreased until T60. Atipamezole increased HR in both groups. Mean arterial blood pressure(MABP) increased from 93mmHg(BL) to 133 within 5 minutes, peaked to 168mmHg at T20 and then gradually decreased to 121mmHg at T60, whilst in group MA, increased from 97mmHg(BL) to 118mmHg within five minutes, but gradually decreased to 104mmHg at T60. CO decreased markedly within five minutes in both groups, but, in group MAA, returned to BL within thirty minutes, whilst in group MA, CO remained decreased until time 60.

These results demonstrated while CO is better maintained, marked changes in MABP and HR warrant to avoid indiscriminate use of medetomidine with atropine in some patient population.