Opioid-sparing effect of a medetomidine constant rate infusion during thoraco-lumbar hemilaminectomy in dogs administered a ketamine infusion.

OBJECTIVE

To evaluate the perioperative opioid-sparing effect of a medetomidine (MED) infusion compared to a saline (SAL) infusion in otherwise healthy dogs undergoing thoraco-lumbar hemilaminectomy surgery.

STUDY

DESIGN

Randomized, partially blinded, clinical study.

ANIMALS: A total of 44 client-owned adult dogs.

METHODS

All dogs were administered a 1 μg kg-1 MED loading dose, followed by a 1.7 μg kg-1 hour-1 constant rate infusion (CRI) intravenously or equivalent volumes of SAL. Infusions were started 10-15 minutes before surgical incision and continued throughout the surgical procedure. All dogs were administered a standardized anaesthetic and analgesic protocol (including a ketamine CRI). Multiparametric monitoring, including invasive arterial blood pressure, was performed. A trained investigator, unaware of the treatment, performed pain scores for 4 hours postoperatively. Rescue analgesia consisted of fentanyl administered intraoperatively and methadone postoperatively. Data were tested for normality and analysed with Fisher's exact test, Mann-Whitney U-test, analysis of variance and Kaplan-Meier survival analysis. Data are shown as median (interquartile range) and p-value was set at < 0.05.

RESULTS

The total dose of fentanyl was significantly lower with MED 0 (0-0.8) μg kg-1 hour-1 compared to SAL 3 (1.8-5.3) μg kg-1 hour-1 (p = 0.004). In the MED group, one dog compared to 12 dogs in the SAL group required a fentanyl CRI (p = 0.001). There were no statistically significant differences between groups regarding the total dose of methadone administered.

CONCLUSIONS AND CLINICAL RELEVANCE: The addition of a low-dose medetomidine CRI to the anaesthetic protocol decreased the need for a fentanyl CRI in otherwise healthy dogs undergoing thoraco-lumbar hemilaminectomy surgery during administration of a ketamine CRI.