Objective: To investigate the feasibility of 2 ultrasound-guided QLB approaches - lateral (QLB-L) and transmuscular (QLB-T) - in calf cadavers. Methods: Ten calf cadavers underwent bilateral QLB at L1 using QLB-L (n=5) or QLB-T (n = 5). Each cadaver received 0.4 mL/kg on one side and 0.6 mL/kg on the other.A 1:2 iohexol:methylene blue mixture was injected under ultrasound guidance. Computed tomography and gross dissection assessed craniocaudal spread and staining of ventral rami and sympathetic trunk segments. Results: The number of stained nerves was similar for both approaches. L1 and L2 were stained in all injections; T13 was stained in all but 1 QLB-L small-volume injection;T12 staining occurred most often with QLB-T small-volume injections (4/5) and in 2/5 injections in the remaining groups; T11 staining was limited (1/5 QLB-L and 2/5 QLB-T;both volumes); T10 to T4 staining occurred once (QLB-T large volume). Conclusions and Relevance: Both approaches were anatomically feasible in calf cadavers and produced injectate spread consistent with potential abdominal wall target coverage. Clinical trials are needed to determine analgesic efficacy and safety.

Background: Standing surgery in horses combining intravenous sedatives, analgesics and local anaesthesia is becoming more popular. Ultrasound guided (USG) peribulbar nerve block (PB) has been described in dogs and humans for facial and ocular surgery, reducing the risk of complications versus retrobulbar nerve block (RB). Objective: To describe a technique for USG PB in horse cadavers. Methods: Landmarks and PB technique were described in two equine cadaver heads (Phase 1), with computed tomography (CT) imaging confirming contrast location and spread. In Phase 2, ten equine cadaver heads were randomised to two operators naïve to the USG PB, with moderate experience with ultrasonography and conventional “blind” RB. Both techniques were demonstrated once. Subsequently, operators performed five USG PB and five RB each, unassisted. Contrast location and spread were evaluated by CT. Injection site success was defined for USG PB as extraconal contrast, and for RB intraconal contrast. Results: Success was 10/10 for USG PB and 0/10 for RB (p < 0.001). Of the RB injections, eight resulted in extraconal contrast and two in the masseter muscle (p = 0.47). Conclusions The USG PB had a high injection site success rate compared with the RB technique; however, we cannot comment on clinical effect. The USG technique was easily learnt, and no potential complications were seen. The USG PB nerve block could have a wide application for use in horses for ocular surgeries (enucleations, eyelid, corneal, cataract surgeries, and ocular analgesia) due to reduced risk of iatrogenic damage. Further clinical studies are needed.

Background: Standing surgery in horses combining intravenous sedatives, analgesics and local anaesthesia is becoming more popular. Ultrasound guided (USG) peribulbar nerve block (PB) has been described in dogs and humans for facial and ocular surgery, reducing the risk of complications versus retrobulbar nerve block (RB). Objective: To describe a technique for USG PB in horse cadavers. Methods: Landmarks and PB technique were described in two equine cadaver heads (Phase 1), with computed tomography (CT) imaging confirming contrast location and spread. In Phase 2, ten equine cadaver heads were randomised to two operators naïve to the USG PB, with moderate experience with ultrasonography and conventional “blind” RB. Both techniques were demonstrated once. Subsequently, operators performed five USG PB and five RB each, unassisted. Contrast location and spread were evaluated by CT. Injection site success was defined for USG PB as extraconal contrast, and for RB intraconal contrast. Results: Success was 10/10 for USG PB and 0/10 for RB (p < 0.001). Of the RB injections, eight resulted in extraconal contrast and two in the masseter muscle (p = 0.47). Conclusions The USG PB had a high injection site success rate compared with the RB technique; however, we cannot comment on clinical effect. The USG technique was easily learnt, and no potential complications were seen. The USG PB nerve block could have a wide application for use in horses for ocular surgeries (enucleations, eyelid, corneal, cataract surgeries, and ocular analgesia) due to reduced risk of iatrogenic damage. Further clinical studies are needed.