HEMODYNAMIC-EFFECTS OF MEDETOMIDINE IN THE DOG - A DOSE TITRATION STUDY

Objective-To characterize the hemodynamic effects of medetomidine admi nistered intravenously at doses ranging from 1 to 20 mu g/kg, and to d etermine whether these effects are dose dependent. Study Design-Prospe ctive randomized multidose trial. Animals-Twenty-five clinically norma l male beagles (5 groups of 5), aged 1 to 4 years and weighing 13.5 +/ - 1.7 kg. Methods-Medetomidine, at a dose of 1, 2, 5, 10, or 20 mu g/k g, was administered intravenously at time 0. Heart rate, arterial pres sure, central venous pressure, mean pulmonary arterial pressure, pulmo nary capillary wedge pressure, body temperature, cardiac output, and p acked cell volume were measured immediately before and at selected tim es after medetomidine administration (3, 7, 10, 20, 30, 40, 50, and 60 minutes in all groups, at 90 minutes for the 10 and 20 mu g/kg groups , and at 120 minutes for the highest dose). Cardiac index, stroke inde x, rate-pressure product, systemic vascular resistance index, pulmonar y vascular resistance index, and left and right ventricular stroke wor k indices were calculated. The degree of sedation was subjectively sco red by an observer who was blinded to the treatment used. Results-Hear t rate, rate-pressure product, cardiac index, and left and right ventr icular stroke work indices decreased below baseline values. Central ve nous pressure and systemic vascular resistance index increased above b aseline measurements. Except in the 2 mu g/kg group, after an initial and short lasting increase, a prolonged decrease in arterial pressure was observed. Conclusions-Hemodynamic changes were observed with the i ntravenous (IV) administration of medetomidine, at any dose. However, the two lowest doses (1 and 2 mu g/kg) produced less cardiovascular de pression. Clinical Relevance-Medetomidine is an alpha-2 adrenoceptor a gonist widely used in dogs, producing sedation, analgesia and cardiova scular depression. When using IV medetomidine, a reduction of the reco mmended dosage (ie, +/-30 to 40 mu g/kg) by up to 6 times did not sign ificantly influence the cardiovascular effects. (C) Copyright 1998 by The American College of Veterinary Surgeons.