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Experimental maxillofacial surgery is commonly performed in pigs; however, locoregional anesthesia of this area has not been described. This study evaluated the feasibility of a novel maxillary nerve block approach. In part I, cadavers were used to determine anatomic landmarks and assess maxillary nerve dye staining by using 0.03 mL kg -1 of a 1:10 mixture of commercial food dye and 0.5% bupivacaine. In part II, 10 additional pig cadavers underwent bilateral ultrasound-guided maxillary nerve blocks by using trans-infraorbital canal needle placement. The maxillary nerve was harvested and scored based on degree of staining (0 and 1, absent or incomplete staining; 2, staining; >1 cm circumferentially). Intracranial and intraconal spread of dye was evaluated. A Kruskal-Wallis test was used to compare infraorbital canal length estimated either externally via landmarks, internally via ultrasound, or actually measured after dissection. In 18 of 20 (90%) injections, successful staining (score = 2) of maxillary nerves was obtained for a nerve length of 2.4 ± 0.3 cm. Two of 20 cases (10%) had inadequate staining (score <2). At dissection of these 2 cases, the needle tip was observed to have collided with an unerupted tooth (third molar). No intracranial or intraconal spread of dye was observed. We detected no statistical differences between the estimated external, estimated internal, or actual dissection methods for measurement of infraorbital canal length ( P = 0.3). Ultrasound-guided trans-infraorbital maxillary nerve block in pigs is a feasible technique, warranting further work to evaluate its in vivo efficacy and safety.

Objective: Novel locoregional techniques use dye studies to confirm successful nerve targeting. The goal was to objectively quantify and compare nerve staining characteristics of dye mixtures commonly reported in the literature using image analysis software., Study Design: Prospective, randomized cadaveric study., Methods: Thirty-six brachial plexus nerves from unpreserved pig cadavers were randomized into three groups of 12: FD (1:10 mixture of blue food dye and bupivacaine 0.5%), MB (methylene blue 1%) and TM (0.1:10 mixture of blue tissue marker and lidocaine 2%). Nerves were immersed in dye for 1, 15, 30 or 60 minutes (n = 3 each). Images of nerves before immersion (baseline) and at each time point with epineurium intact (superficial staining) and after longitudinal bisection (deep staining) were processed using image analysis software. Color saturation values were divided into quartiles (dark, medium-dark, medium-light or light). Percentage of stained nerve area in each quartile was calculated and compared using two-way anova., Results: Superficially, at minute 1, dark saturation covered 40% of nerve area in FD versus 19% in MB (p = 0.04) and 0% in TM (p < 0.0001). In bisected nerves, dark and medium-dark saturations occurred only in FD; medium-light saturation comprised anywhere from 4% to 22.5% over time in FD versus <1% at any time in MB (p = 1.000; p = 0.343; p = 0.383; p = 0.262). Deep staining was not found in TM at any point., Conclusion and Clinical Relevance: Food dye rapidly stains superficial and deep nerve layers. Based on these characteristics, investigators can choose the appropriate dye for their study., (Copyright © 2023 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)

Objective: To evaluate the duration and analgesic quality of bupivacaine mixed with dexmedetomidine (BUP-DEX) or bupivacaine liposome suspension (BLS) administered as a transverse abdominis plane (TAP) block, compared with a negative control (no TAP block; CTRL) in dogs., Animals: 26 mixed-breed shelter dogs undergoing elective ovariohysterectomy between January 28 and December 8, 2020., Procedures: Each dog was randomly assigned to receive either an ultrasound-guided TAP block with either BUP-DEX or BLS or to receive no TAP block at time 0 after induction of general anesthesia. Superficial and abdominal wall pain scores were evaluated before time 0 and at 4, 6, 12, 24, 48, 72, and 96 hours later. Additionally, sedation scores and time to return of various behaviors, such as eating or drinking, were compared., Results: The CTRL group had significantly greater pain scores than the BUP-DEX and BLS groups, but no differences were found between the BUP-DEX and BLS groups. Postoperatively, significantly more dogs needed rescue analgesia and the time to need it was shorter for the CTRL group, compared with the BUP-DEX or BLS groups. Additionally, the CTRL group had greater sedation scores than the other 2 groups. No significant differences were observed in any of the evaluated outcome variables such as eating or drinking., Clinical Relevance: A TAP block appeared to provide adequate postoperative analgesia for abdominal surgery in the dogs of the present study undergoing elective ovariohysterectomy. The BLS TAP block did not appear to provide any extra benefit beyond what BUP-DEX TAP block added under these specific conditions.