Comparison of anesthesia with a morphine-lidocaine-ketamine infusion or a morphine-lidocaine epidural on time to extubation in dogs

Objective: To evaluate and compare the time to extubation in two commonly used methods of analgesia in dogs undergoing elective pelvic limb orthopedic procedures. Study design: Prospective, randomized, double-blinded clinical study. Animals: Twenty-five adult, client-owned, healthy dogs aged 4.4 ± 1.6 years and weighing 38.5 ±3.5 kg. Methods: All dogs were premedicated with dexmedetomidine (5-10 μg kg^-1) intramuscularly (IM) and anesthesia was induced with propofol (2-6 mg kg^-1) intravenously (IV). Atipamazole (0.05-0.1 mg kg^-1) was administered IM after instrumentation. Anesthesia was maintained with isoflurane in oxygen. Dogs were randomly assigned to one of two groups. In one group, morphine (0.1 mg kg^-1) and lidocaine (2% lidocaine added to a total volume of 0.2 mL kg^-1) were administered epidurally and a saline placebo constant rate infusion (CRI) was administered IV (group EPI). In the other group (group MLK), morphine (4 μg kg^-1 minute^-1), lidocaine (50 μg kg^-1 minute^-1) and ketamine (10 μg kg^-1 minute^-1) were administered as an IV CRI and a saline placebo was administered by epidural injection. Temperature at the discontinuation of isoflurane, temperature at extubation, time to extubation, duration of inhalation anesthesia and duration of surgery were recorded. Results: No significant differences between the groups were found in time to extubation, temperature at the end of surgery, temperature at extubation and total surgical time. Total anesthesia time was significantly longer in group EPI. Conclusions and clinical relevance: Administration of MLK at the doses reported in this study did not prolong the time to extubation in comparison with a morphine-lidocaine epidural nerve block. The results indicate that concern over prolonging the time to extubation is not a reason to avoid the administration of MLK.