Intraoperative opioid-sparing effect of a quadratus lumborum block using low-concentration bupivacaine and dexmedetomidine in cats undergoing ovariohysterectomy

Objectives This study aimed to evaluate the intraoperative opioid-sparing effect of quadratus lumborum block (QLB) using low-concentration bupivacaine combined with dexmedetomidine in cats undergoing ovariohysterectomy. Methods A total of 28 cats scheduled for ovariohysterectomy and classified as American Society of Anaesthesiologists status I were enrolled and randomly allocated to either a bupivacaine (0.125%) and saline (BS) or bupivacaine (0.125%) and dexmedetomidine (1 µg/kg) (BD) group. The cats underwent ultrasound-guided QLB in sternal recumbency using the allocated solution. If heart rate or mean arterial pressure increased by 20% or more from baseline during surgery, fentanyl (2 µg/kg IV) was administered as rescue analgesia. Postoperative pain was assessed 1, 2, 3, 6 and 12 h after extubation using the Short-Form UNESP-Botucatu Multidimensional Composite Pain Scale. Buprenorphine (0.02 mg/kg IM) was administered if the pain score was 4/12 or higher. Results The cumulative intraoperative dose of fentanyl was significantly lower in the BD group (1 µg/kg [range 0–6]) than in the BS group (2 µg/kg [range 0–8]; P = 0.030). No significant difference was observed between the groups in terms of the proportion of cats requiring intraoperative or postoperative rescue analgesia, postoperative pain scores at any time point, intraoperative physiological parameters or time-related variables. Conclusions and relevance QLB performed in sternal recumbency using low-concentration bupivacaine with dexmedetomidine was associated with a modest reduction in intraoperative opioid requirements during ovariohysterectomy in cats. However, as this study design could not differentiate between the local and systemic effects of dexmedetomidine, further research is needed to clarify their relative contributions and determine the optimal adjunctive dose.