Addition of magnesium sulphate to ropivacaine for spinal analgesia in dogs undergoing tibial plateau levelling osteotomy

• Published in: The veterinary journal (1997) 2016-03, Vol.209, p.163-168
• Main Authors: Adami, C., Casoni, D., Noussitou, F., Rytz, U., Spadavecchia, C.
• Format: Article
• Language: English
• Subjects: Amides - administration & dosage; Analgesia; Analgesia - veterinary; Analgesics - administration & dosage; Analgesics, Opioid - administration & dosage; Anesthetics, Local - administration & dosage; Animals; Buprenorphine - administration & dosage; Dog; Dogs - surgery; Fentanyl - administration & dosage; Magnesium Sulfate - administration & dosage; Magnesium sulphate; Osteotomy - veterinary; Pain Measurement - veterinary; Pain, Postoperative - veterinary; Prospective Studies; Ropivacaine; Spinal anaesthesia
• ISSN: 1090-0233; 1532-2971
• DOI: 10.1016/j.tvjl.2015.11.017

•Spinal magnesium sulphate added to ropivacaine enhances duration and intensity of the analgesia provided by ropivacaine in dogs undergoing TPLO, but also carries the potential for prolonged, though transient, motor block.•This can result in patient discomfort for several hours after surgery, and also make the post-operative care more demanding and expensive.•Further studies may be necessary to identify still effective, though safer, magnesium doses to be administered spinally to dogs. The aim of this blinded, randomised, prospective clinical trial was to determine whether the addition of magnesium sulphate to spinally-administered ropivacaine would improve peri-operative analgesia without impairing motor function in dogs undergoing orthopaedic surgery. Twenty client-owned dogs undergoing tibial plateau levelling osteotomy were randomly assigned to one of two treatment groups: group C (control, receiving hyperbaric ropivacaine by the spinal route) or group M (magnesium, receiving a hyperbaric combination of magnesium sulphate and ropivacaine by the spinal route). During surgery, changes in physiological variables above baseline were used to evaluate nociception. Arterial blood was collected before and after spinal injection, at four time points, to monitor plasma magnesium concentrations. Post-operatively, pain was assessed with a modified Sammarco pain score, a Glasgow pain scale and a visual analogue scale, while motor function was evaluated with a modified Tarlov scale. Assessments were performed at recovery and 1, 2 and 3 h thereafter. Fentanyl and buprenorphine were administered as rescue analgesics in the intra- and post-operative periods, respectively. Plasma magnesium concentrations did not increase after spinal injection compared to baseline. Group M required less intra-operative fentanyl, had lower Glasgow pain scores and experienced analgesia of longer duration than group C (527.0 ± 341.0 min vs. 176.0 ± 109.0 min). However, in group M the motor block was significantly longer, which limits the usefulness of magnesium for spinal analgesia at the investigated dose. Further research is needed to determine a clinically effective dose with shorter duration of motor block for magnesium used as an additive to spinal analgesic agents.