Intratesticular mepivacaine versus lidocaine in anaesthetised horses undergoing Henderson castration

Background In horses undergoing castration, direct comparison of intratesticular lidocaine vs mepivacaine as analgesic adjuncts has not yet been analysed. Objective To compare the effects of intratesticular lidocaine and mepivacaine during equine castration using the Henderson drill under total intravenous anesthesia. Study design Randomised, double‐blinded clinical study. Methods Thirty‐four stallions were anaesthetised using xylazine‐ketamine and randomly selected to receive 10 mL either lidocaine or mepivacaine injected into each testicle. Both surgeon and anaesthetist were blinded to the selected treatment. A total of 5 minutes were required to pass between injection and first incision. Routine castration using a Henderson drill was performed. Heart rate, respiratory rate and SpO2 were serially recorded. Total surgical time, time prior to clamping of each testicle and time to second incision were recorded. Cremaster muscle relaxation, surgical quality scores, number of additional ketamine boluses, recovery time and recovery quality were assessed between groups. Results Cremaster relaxation scores were significantly better for the mepivacaine group over the lidocaine group on a 1‐3 scoring system (1 being most relaxed, 3 being least). The average cremaster relaxation score on both testicles treated with mepivacaine was 1 compared to the lidocaine treatment averaging 2 [P = .03 first testicle; P = .04 second testicle]. The lidocaine group had an increased number of horses requiring additional ketamine (25% of horses) compared to the mepivacaine group (16% of horses). No other significant differences were observed between the groups. Main limitations The use of only one injection method and lack of post‐operative pain scoring limit the conclusions that can be drawn from these results. Conclusion Intratesticular mepivacaine when compared with intratesticular lidocaine results in improved cremaster muscle relaxation when only waiting five min prior to the start of the procedure.