Evaluation of postoperative analgesia of methadone, ketamine or their associations in cats undergoing ovariohysterectomy

The prevention and control of pain are basic components to have an adequate anesthesia. The aim of this study was to investigate the postoperative analgesia of ketamine in subanestesica dose, of methadone and the association of both intramuscularly in cats. A total of 24 cats proven healthy were referred for elective ovariossalpingohisterectomia. The day before the beginning of the experiment animals were anesthetized for placing a catheter in the jugular vein for subsequent blood sampling for measurement of serum concentration of cortisol. The next day, animals were randomly allocated to three groups (n = 8), which received ketamine (GC) at a dose of 0.5mg/kg; methadone (GM) at a dose of 0.3mg/kg; methadone and ketamine (GCM) at doses of 0.5mg/kg and 0.3mg/kg, respectively, all in the intramuscular route. All groups received the drug 20 minutes before induction of anesthesia, which was performed with propofol and maintained with isoflurane. The parameters evaluated were the measurement of cortisol in moments M0 (baseline-before surgery), M1(intraoperative), M2, M3, M4, M8, M12 and M24 (2,3,4,8,12 and 24 hours after the end of surgery) and evaluation of pain score by multidimensional scale of acute pain in cats in the moments M0, M2, M3, M4, M8, M12 and M24. The cortisol levels were higher in GC compared to GM and GCM in M2 and M3. Pain scores were higher in GC in moments M2 and M3 compared to GM and GCM, respectively. In summation of points in M2, GC showed higher values than GM and GCM, and M4, GC obtained values greater than GCM. Comparing the number of rescues postoperatively in GC 8/8 of animals required rescue, in GM /8 and in GCM 3/8. It was concluded that the combination of methadone and ketamine in cats undergoing elective OSH provides adequate postoperative analgesia, reducing the requirement for analgesics in the postoperative period.