Cardiopulmonary effects of medetomidine in heartworm-infected and noninfected dogs

Abstract

Summary Medetomidine, an investigational drug indicated for clinical use as a short-term chemical restraint in dogs, was evaluated for its cardiopulmonary effects, in 10 naturally heartworm-infected (HW+) and 10 noninfected (hw−) Beagles. The drug was randomly administered IV (30 μg/kg of body weight) and IM (40 μg/kg) in single injections to all dogs. Heart rate, respiratory rate, ecg, blood gas tensions, blood pH, central venous and arterial pressures were measured at 0, 15, 30, 60, 90, 120, and 180 minutes. Medetomidine induced an immediate significant (P ≤ 0.001) increase in mean arterial blood pressure followed by decreased blood pressure that remained below normal throughout the study in both groups, irrespective of route of administration. Medetomidine increased central venous pressure, over time, for both groups and both routes of administration. Heart and respiratory rates were significantly (P ≤ 0.001) decreased after medetomidine administration and remained reduced for the duration of the study in all dogs. The ecg variables were not significantly different between groups or between routes of administration. The HW+ dogs tended to have higher mean Pao2 than did HW− dogs at several postinjection determination times, particularly when the drug was administered IM. The Pao2; decreased during the first 30 minutes in both groups and tended to increase gradually thereafter. The pH decreased over time for both groups and both routes. A significant (P ≤ 0.05) decrease in pH was seen in the HW− dogs, compared with HW+ dogs at each measuring time for both routes. The Paco2 did not significantly change for groups or routes. In general, bradycardia was the predominant cardiovascular effect seen after medetomidine administration in all dogs, irrespective of route. Lowering of blood pressure and heart rate (after a transient blood pressure increase) was synchronized with sedation in these dogs. The overall clinical response with regard to cardiopulmonary effects in HW+ dogs was similar to that in HW− dogs.