Post-surgical Evaluation of the Analgesic Impact of Epidural Tramadol, when Associated with Levobupivacaine, in Bitches Undergoing Mastectomy and Ovariohysterectomy

Abstract

Background:Mammary tumors are the most common neoplasms in female dogs. Surgical removal of the mammary gland chain is considered the standard treatment and is usually performed along with ovariohysterectomy (OH) to suppress ovarian hormonal influence. Mastectomies cause moderate to severe pain and require preferential multimodal analgesic protocols. The aim of this study was to compare the postoperative analgesic efficacy and the recovery times on female dogs undergoing mastectomies and OH between those treated with epidural levobupivacaine alone and those treated with associated doses of tramadol and anesthetized with propofol.Materials, Methods & Results:Eighteen female dogs were pretreated with acepromazine (0.03 mg/kg), using propofol (4 mg/kg)for induction andanesthesia maintenance. The dogs were randomly divided into three groups (n = 6) treated with epidural anesthesia with levobupivacaine alone at 1.5 mg/kg (GL) or associated with tramadol at doses of 2 mg/kg (GLT2) or 4 mg/kg (GLT4). After anesthesia,the mean propofol infusion rate for each groupwere calculed. During the postoperative period,the degree of analgesia according to the University of Melbourne Pain Scale for 6 hours were determined, considering seven time points for evaluation (M30, M60, M90, M120, M180, M240, and M360). Supplemental analgesia with morphine (0.5 mg/kg) to those dogs with scores ≥13 were provided. During the recovery period,the time intervals between the end of anesthesia, and the following events: extubation (EX), the first head movement (MC), and the establishment of sternal (PE) and quadrupedal (PQ) positions were measured. The data were subjected to the Friedman test for analysis of non-parametric variables within the same group and to the Mann–Whitney test for independent variables, comparing the mean scores between groups (statistical significance was set at P<0.05). In the GL group, a higher mean propofol infusion rate than in either the GLT2 or GLT4 groups were found. The EX, PE, and PQ times were similar between the groups with a lower MC interval (P=0.041) for dogs in the GLT2 group. The pain assessment revealed higher scores for dogs in the GL group than for those in the GLT4 group (M30 to M120 and M360). Over time, the initial scores increased after M90 (GL group) and afterM120 (in all groups) andadditional analgesia were required only in GL dogs.Discussion:Mammary tumors were more frequent in middle-aged and elderly female dogs, corroborating current literary data. Regarding anesthesia recovery, no differences in the time for extubation and sternal and quadrupedal positions were found, probably due to similar propofol infusion times and to similar metabolism among the dogs, independent of the higher mean infusion rates used in the group treated only with the local anesthetic. The post-surgical analgesic evaluation revealed lower pain scores in the groups in which tramadol was associated with levobupivacaine, in agreement with studies reporting its analgesic potential to approach surgical pain at doses ranging from 1 to 4 mg/kg. However, even lower scores with the highest dose of the proposed opioid were detected, suggesting improved effectiveness for occupying opioid and monoaminergic pathway receptors. Considering the results, epidural anesthesia with levobupivacaine and tramadol seems to provide adequate post-surgical analgesia for a minimum period of 6 hours, and the best comfort is obtained with a dose of 4 mg/kg of opioid.