RESUMO
OBJECTIVE: To compare the cardiovascular effects of a combination of medetomidine and vatinoxan (MVX) versus medetomidine (MED) alone administered intramuscularly (IM) and to determine whether heart rate (HR) can be used as a surrogate for cardiac output (CO) after the use of medetomidine with or without vatinoxan. STUDY DESIGN: A randomized, blinded, experimental, crossover study. ANIMALS: A group of eight healthy Beagle dogs aged 4.6 (2.3-9.4) years and weighing 12.9 (9-14.7) kg, median (range). METHODS: Each dog was injected with 1 mg m-2 medetomidine with or without 20 mg m-2 vatinoxan IM with a washout period of 7 days. Cardiovascular data and arterial and mixed venous blood gas samples were collected at baseline, 5, 10, 15, 20, 35, 45, 60, 90 and 120 minutes after treatment administration. CO was measured at all time points via thermodilution. Differences between treatments, period and sequence were evaluated with repeated measures analysis of covariance and the relationship between HR and CO was assessed with a repeated measures analysis of variance; p values < 0.05 were deemed significant. RESULTS: The CO was 47-96% lower after MED than after MVX (p < 0.0001). Increases in systemic, pulmonary arterial and right atrial pressures and oxygen extraction ratio were significantly higher after MED than after MVX (all p < 0.0001). HR was significantly lower after MED and the linear relationship to CO was significant (p < 0.0001). CONCLUSIONS AND CLINICAL RELEVANCE: Overall, MED affected the cardiovascular system more negatively than MVX, and the difference in cardiovascular function between the treatments can be considered clinically relevant. HR was linearly related to CO, and decreases in HR reflected cardiac performance for dogs sedated with medetomidine with or without vatinoxan.