Postoperative Pain Management in a Sheep Using Continuous Epidural Morphine

Background: Although ruminants experience pain like other species, diagnosis and treatment may be imprecise and challenging, especially because of lack of recognition and restraint of therapeutic resources. In addition to the restrictions inherent in the species, organic dysfunctions may further restrict the analgesic arsenal, making it necessary to find viable and effective alternative for pain control. The continuous administration of opioids in the epidural space has been highlightedas an analgesic resource in several species. However, until this moment, there are few information on this practice in ruminants. Therefore, the aim of this study was to describe the use of continuous epidural infusion of morphine in a sheep undergoing to urethrostomy with a history of chronic pain and urolithiasis.Case: A 3-year-old Santa Ines sheep, weighting 110 kg, was presented to the Veterinary Hospital of Federal University of Bahia with history of recurrent urolithiasis, lameness, severe pain and continuous use of nonsteroidal anti-inflammatory drug (NSAID). The findings of the physical examination, imaging and laboratory tests revealed possible abomasum inflammation, chronic laminitis, left humerus-radioulnar osteoarthritis and urethral urolithiasis with uremia. A clinical stabilization of the animal was performed, including an interruption of the use of the NSAID and the administration of fluid, urinary acidifier (ammonium chloride), histamine H2 receptor antagonist (ranitidine), cytoprotectant (sucralfate), antibiotic (norfloxacin) and dipyrone. After 3 days, urethrostomy was performed followed by the implantation of an epidural catheter (19G) in the lumbosacral space (L7 - S1) by means of a Tuohy needle (18G), after the surgical procedure. Administration of morphine (0.1 mg kg-1) through the catheter at 24-h intervals, associated with dipyrone (25 mg kg-1) intravenously (IV), every 8 h, over a 5-day period, was the postoperative analgesic protocol chosen. The data of heart rate (HR), respiratory rate (f),rectal temperature (T °C), ruminal movements (RM) and possible behavior related to pain were registered at intervals of four-hours until the fifth day after surgery. After 24 h postoperative, stability of the variables (HR, f, T °C) with increased RM concomitant to the interest for food was verified. On the fifth postoperative day, the animal was hydrated, visibly comfortable and with normal levels of serum creatinine.Discussion: Considering the initial clinical status involving renal insufficiency and significant gastric abnormalities, the use of NSAIDs was immediately disregarded. However, the need to relieved musculoskeletal and postoperative pain, has raised interest in the use of morphine, whose literature refers duration of up to 24 h in other species, with reduced adverse effects compared to systemic administration, due to the considerably lower dose. Dipyrone was incorporated into the protocol forproviding visceral analgesia and minimal effects on the organic functions. During the 5-days of evaluation, the signs of well-being presented by the animal associated to the stability of vital parameters, feeding and satisfactory ruminal activity attested to the viability of the protocol tested. It was concluded that the use of morphine, through the continuous epiduralroute, contributed to the relief of postoperative pain, reestablishment of the organic functions and patient welfare, being suitable as an analgesic alternative to NSAID use in sheep.Keywords: ovine, analgesia, opioid, epidural