Abstract
Objective
To characterize the hemodynamic effects of continuous rate infusions (CRI) of medetomidine
administered at doses ranging from 0 to 3 μg kg−1 hour−1.
Study design
Prospective, blinded, randomized experimental trial.
Animals
Six adult purpose-bred mongrel dogs.
Methods
Anesthesia was induced with sevoflurane for placement of arterial and venous catheters.
Dogs recovered from anesthesia after which baseline hemodynamic measurements were
obtained via lithium dilution cardiac output (CO) determination, with subsequent measurements
via pulse power analysis to provide continuous CO determinations. Medetomidine, 1,
2, or 3 μg kg−1 hour−1 or a volume equivalent placebo, was administered via CRI for 60 minutes. Systolic,
mean, and diastolic arterial pressure, heart rate (HR), CO and stroke volume were
measured and stroke index (SI), cardiac index (CI), total peripheral resistance (TPR),
and total peripheral resistance index (TPRI) were calculated at 3, 7, 10, 20, 30,
45, 60, 90, and 120 minutes from the start of the infusion.
Results
Increase in dose decreased SI by 25%, 19%, and 30%, HR by 33%, 57%, and 60%, CI by
50%, 65%, 70% and increased TPRI by 109%, 235%, and 222% from baseline to the 60-minute
measurement for the 1, 2, and 3 μg kg−1 hour−1 doses, respectively. HR, TPRI, and CI all showed significant differences over the
duration of the study from the placebo treatment.
Conclusions
Medetomidine CRI produces clinically relevant changes in CO, TPR, and HR. The demonstrated
decrease in CO is largely because of bradycardia and the degree of cardiovascular
depression appears to be dose-dependent. These findings are consistent with previously
described hemodynamic changes with single bolus administration of medetomidine.
Clinical relevance
Low-dose medetomidine CRIs produce clinically relevant hemodynamic depression at doses
as low as 1 μg kg−1 hour−1 and should be used cautiously in dogs.
Keywords
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Article info
Publication history
Accepted:
April 19,
2009
Received:
September 3,
2008
Identification
Copyright
© 2010 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Inc. All rights reserved.
