Margherita Galosi Luca Pennasilico Angela Palumbo Piccionello Federica Serino Francesca Tosi Sara Sassaroli Valentina Riccio Alessio Angorini Alberto Salvaggio Caterina Di Bella ^*

• School of Bioscience and Veterinary Medicine, Camerino, Italy

Introduction: Magnesium Sulphate (MgSO4 ) is commonly used in human medicine for the management of perioperative pain. However, in veterinary medicine, the use of MgSO4 has not been evaluated for its analgesic efficacy in dogs. The aim of this study was to evaluate the perioperative analgesic efficacy of MgSO4 in combination with Ketamine in dogs undergoing TPLO. Our hypothesis is that MgSO4 plus ketamine have a synergistic action in the management of pain. Method: twenty adult mixed breed dogs with average age 5.9±2.6 years and weight 27.8±9.2 kg were included in this study. Dogs were randomly assigned to two groups. The MK group received ketamine (0.5 mg/kg as starting bolus followed by continuous infusion rate at 1 mg/kg/h). At the end of the ketamine bolus, MgSO4 (50 mg/kg over 15 minutes) was administered by the same route, followed by a constant rate infusion (CRI) at 15 mg/kg/h, IV. K group received a bolus of ketamine followed by a CRI at the same dosage described in MK group. Main cardiorespiratory parameters were recorded 10 minutes before the start of surgery (BASE), after the ketamine bolus (T1) and the MgSO4 bolus (T2), during the skin incision (SKIN), the osteotomy (OSTEOTOMY) and skin suturing (SUTURE). In the postoperative period, the short form of Glasgow Composite Pain scale (SF-CMPS) was used to assess pain at 30, 60, 120, and 180 minutes after extubation. The main blood electrolytes (Mg 2+ , Ca 2+ , Na + , K + ) were analyzed at BASE, T2, OSTEOTOMY, SUTURE and T3 (one hour after stopping MgSO4 infusion). Number of rescue analgesia and administration times were recorded both in the intra-and postoperative period. Results: in K group 7/10 dogs required intraoperatory rescue analgesia compared to MK group (3/10). Furthermore, mean arterial pressure and heart rate were significantly higher at OSTEOTOMY compared to BASE time in both groups. In the postoperative period, at T120, ICMPS-SF score was higher in K group than MK group. Conclusions: the administration of MgSO 4 could guarantee better analgesia in the perioperative period in dogs undergoing TPLO, performing a synergistic action with ketamine.