The hemodynamic effects of medetomidine continuous rate infusions in the dog.
OBJECTIVE
To characterize the hemodynamic effects of continuous rate infusions (CRI) of medetomidine administered at doses ranging from 0 to 3 microg kg(-1) hour(-1).


METHODS
Prospective, blinded, randomized experimental trial.


METHODS
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 microg 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 microg 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.


CONCLUSIONS
Low-dose medetomidine CRIs produce clinically relevant hemodynamic depression at doses as low as 1 microg kg(-1) hour(-1) and should be used cautiously in dogs.
Department of Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA. jcarter@rossvet.edu.kn
Jennifer E
JE
Carter
Nigel B
NB
Campbell
Lysa P
LP
Posner
Cliff
C
Swanson
D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007262:Infusions, Intravenous / Q000662:veterinary; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D013318:Stroke Volume / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects
D018712:Analgesics, Non-Narcotic; D020926:Medetomidine