A preoperative bupivacaine retrobulbar block offers superior antinociception compared with an intraoperative splash block in dogs undergoing enucleation.

Purpose: Investigate nociception differences in dogs undergoing enucleation administered bupivacaine either via preoperative retrobulbar block (pRB) or intraoperative splash block (iSB). Methods: Prospective, randomized, double-masked, clinical comparison study. Dogs undergoing unilateral enucleation were randomized to two groups: one received bupivacaine pRB and saline iSB of the same volume, and the other received saline pRB and bupivacaine iSB. The following intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO2 (EtCO2); systolic, mean, and diastolic arterial blood pressure (SAP, MAP, and DAP respectively); inspired end-tidal isoflurane concentration (EtISOIns), and expired end-tidal isoflurane concentration (EtISOExp). Pain scores were recorded pre- and postoperatively. Analgesic rescue was documented. Surgical hemorrhage and postoperative bruising and swelling were graded subjectively by the surgeon (HDW) and study coordinator (AEZ). Results: A significant (P=.0399) increase from baseline in overall mean heart rate was recorded in iSB bupivacaine patients (n=11) compared with pRB bupivacaine patients (n=11), with no significant differences in other intraoperative physiologic parameters, or pain scores. More analgesic rescue events occurred in iSB bupivacaine patients compared to pRB bupivacaine patients. A near-significant increase in intraoperative bleeding (P=.0519), and a significant increase in bruising (P=.0382) and swelling (P=.0223) was noted in the iSB bupivacaine group. Conclusions: Preoperative retrobulbar block bupivacaine is more effective than an iSB bupivacaine at controlling both intraoperative and postoperative nociception in dogs undergoing enucleation. Additionally, iSB causes more postoperative bruising and swelling and may be associated with increased intraoperative hemorrhage.