Comparison between the Effect of Lidocaine or Ropivacaine Hematoma Block and of Different Timings of Administration on Post-Operative Pain in Dogs Undergoing Osteosynthesis of Long-Bone Fractures

SIMPLE SUMMARY: Post-operative pain after fracture fixation in dogs can be severe. We already know that intra-operative bupivacaine hematoma block (HB, the infusion of local anaesthetic–bupivacaineto the fracture site during the operation) is effective in reducing post-operative pain in dogs undergoing long-bone fracture fixation (Dimopoulou et al. 2017). The aim of the present study was to compare the efficacy of other local anaesthetics, such as lidocaine or ropivacaine, for post-operative pain relief when administered via an HB in the same clinical scenario and also to investigate which is the best intra-operative time point to perform the HB in order to achieve better post-operative pain relief. For this aim, we infused two different local anaesthetics (lidocaine or ropivacaine) at the same surgical time point to compare their analgesic efficacy but also the same local anaesthetic (ropivacaine) at three different distinct surgical time points. Post-operative pain was estimated with the use of the University of Melbourne Pain Scale (a multimodal pain scale) and an algometer (a device that measures the mechanical pain threshold). The results of the present study indicate that the dogs that received a lidocaine HB experienced better post-operative pain relief than those who received a ropivacaine HB. Furthermore, the dogs that received the HB (ropivacaine) right before surgical closure had better post-operative pain relief. ABSTRACT: Objective: We aimed to compare the efficacy of intra-operative lidocaine hematoma block (HB) to ropivacaine HB and to compare the efficacy of different timings of ropivacaine HB in controlling post-operative pain in dogs undergoing the osteosynthesis of long-bone fractures. Study Design: We conducted a randomized, blinded, prospective clinical study. Animals: Forty-eight dogs with long-bone fractures were included and were randomly allocated to four groups: lidocaine (L), ropivacaine (Rmid), ropivacaine pre- (Rpre) and ropivacaine post- (Rpost) groups. Methods: The dogs in group L (n = 14) and in group Rmid (n = 11) received a lidocaine or ropivacaine HB, respectively, after fracture reduction and before osteosynthesis material placement. Rpre dogs (n = 11) received ropivacaine HB before fracture reduction, and Rpost dogs (n = 12) received ropivacaine HB after osteosynthesis material placement. Eight post-operative pain assessments were performed using the University of Melbourne Pain Scale (UMPS) and an algometer. Rescue analgesia was administered based on UMPS scoring. For data analysis, the Shapiro–Wilk test of normality, chi-square, Student t test and Split Plot analysis were used. The level of significance was set at α = 0.05. Results: Rescue analgesia was administered to one dog in group L, one in group Rmid and one in group Rpost, with no significant differences detected. Compared to group Rmid, group L dogs exhibited significantly higher mean mechanical pain thresholds (p = 0.049) and lower mean UMPS scores (p = 0.001). Group Rpost dogs had statistically significantly higher mean pain thresholds compared to group Rmid (p = 0.009). Clinical Implications: When performed after fracture reduction and before osteosynthesis material placement, lidocaine HB seems to be more effective than ropivacaine HB in controlling post-operative pain in dogs undergoing osteosynthesis of long-bone fractures. The administration of ropivacaine HB after osteosynthesis material placement seems to be more effective than administration after fracture reduction and before osteosynthesis material placement or administration before fracture reduction in controlling post-operative pain in dogs undergoing osteosynthesis of long-bone fractures.