Objective: To compare the effects of morphine-lidocaine-ketamine (MLK) and fentanyl-lidocaine-ketamine (FLK) combinations administered as constant rate infusions (CRIs) during and after veterinary procedures on postprocedure rectal temperature in dogs.
Animals: 32 clinically normal client-owned dogs undergoing nonemergent procedures.
Procedures: Dogs were randomly assigned to receive an MLK or FLK combination (16 dogs/group). During the procedure, each dog received 2% lidocaine hydrochloride (1 mg/kg/h; both groups), ketamine hydrochloride (0.6 mg/kg/h; both groups), and morphine (0.36 mg/kg/h; MLK group) or fentanyl (4 μg/kg/h; FLK group) via CRI for analgesia; esophageal temperature was maintained at 37° to 39°C. At extubation, each drug dose in each assigned combination was halved and administered (via CRI) for 12 additional hours for postprocedure analgesia. Rectal temperature and other data were recorded at baseline (prior to administration of premedicants), extubation (0 hours), and 0.5, 1.5, 3, 6, and 12 hours thereafter.
Results: Mean postprocedure rectal temperature was significantly lower at each postextubation time point for the MLK group, compared with corresponding values for the FLK group. Compared with the baseline value, mean postprocedure rectal temperature was significantly lower at 0, 0.5, 1.5, and 3 hours for the FLK group and at all postprocedure time points for the MLK group. Hypothermia (rectal temperature < 37°C) was detected at ≥ 1 postprocedure time point more often in dogs in the MLK group (9/16) than in the FLK group (1/16).
Conclusions and clinical relevance: Dogs that received an MLK combination for analgesia during and after a veterinary procedure developed hypothermia more commonly than did dogs that received an FLK combination under similar conditions.