Evaluation of Two Protocols for Analgesia during Total Unilateral Mastectomy in Bitches

Background: Proper evaluation of pain is essential to select effective anesthetic protocols in surgical procedures in animals. Pain assessment can be accomplished during the perioperative period by measuring several physiological parameters, such as heart and respiratory rates. Measuring serum levels of cortisol and glucose is one of the most commonly used methods to assess the effectiveness of protocols for pain control. The aim of this study was to compare two analgesic protocols in dogs undergoing unilateral total mastectomy, a surgery that can cause moderate-to-severe pain in dogs. Materials, Methods & Results: Eighteen female dogs seen at the Veterinary Hospital of the University of Southern Santa Catarina, Brazil, were recruited for this study, without stratification by breed and age, except for brachycephalic breeds. The animals were divided into two groups: 1) FLK group, in which the animals received preoperative ketamine (5 mg/ kg, IM) and midazolam (0.3 mg/kg, IM), an IV bolus of fentanyl (0.004 mg/kg), lidocaine (2 mg/kg) and ketamine (0.5 mg/kg), and then a combination of fentanyl (0.008 mg/kg/h), ketamine (0.6 mg/kg/h) and lidocaine (2 mg/kg/h) diluted in normal saline solution were infused at a rate of 10 mL/kg/h until the end of the surgical procedure; 2) AM group, in which the animals received preoperative morphine (0.5 mg/kg, IM) and acepromazine (0.05 mg/kg, IM). In both groups, anesthesia was induced by using propofol (6 mg/kg, IV) and maintained with isoflurane. Blood samples were collected by jugular venipuncture (4 mL) in the preoperative and postoperative periods to evaluate serum levels of cortisol and glucose. Statistical analysis was carried out using the two-way analysis of variance (ANOVA) for repeated measures, followed by the Tukey test (P < 0.05). Cortisol levels showed no significant difference between pre- and postoperative periods. Glucose levels showed a significant difference between pre- and postoperative periods in the AM group (P = 0.001). The respiratory rate showed a significant difference between groups at 10 (T10) min after induction (P < 0.001). Discussion: In this study, 67% of the experimental animals were mixed-breed dogs. The average weight was 16.9 ± 10.1 kg. The most frequent age group seen at the Veterinary Hospital was 8-10 years, which is in accordance with other published studies on female dogs with mean age of 10 years. The significant difference in the respiratory rate at T10 can be explained by the respiratory depression caused by a bolus administration of fentanyl in the FLK group. Both protocols were similar in this study; however, higher values of cortisol and glucose, even above the physiological reference values, were observed in the AM group as compared to the FLK group. These higher values must be taken into consideration due to their clinical importance, given that consequences of stress include several deleterious effects, such as immunosuppression, delayed wound healing, and acceleration of disease processes. Findings from this study indicate that the use of a multimodal analgesia protocol, such as the one used in the FLK group, is probably the best alternative for patients submitted to unilateral total mastectomy.