Evaluation of local anesthetic blockade in cats undergoing castration in a high-quality, high-volume spay/neuter setting: a randomized, blinded, placebo-controlled trial.

ObjectivesThe objective of this prospective study was to compare the nociceptive blunting and analgesic efficacy of two different local anesthetic solutions (lidocaine and a mixture of lidocaine plus bupivacaine) and a placebo for cat castrations in a high-quality, high-volume spay/neuter (HQHVSN) clinic as an adjunct to standard HQHVSN anesthetic protocols.MethodsA total of 88 healthy, shelter-owned male cats presenting to an HQHVSN clinic in the northeastern USA between August 2019 and October 2020 were enrolled in this blinded, randomized, placebo-controlled trial. Cats were randomized to receive an intratesticular injection of saline placebo (SP group; n = 32), lidocaine 1 mg/kg (L group; n = 34) or a mixture of lidocaine 1 mg/kg and bupivacaine 1 mg/kg (LB group; n = 22) before routine castration. Other than the use of randomized local anesthetic blocks, all standard HQHVSN protocols for anesthesia and surgery were followed. Measured variables included perioperative heart rates, surgeon satisfaction with anesthetic depth, surgeon satisfaction with tissue quality, postoperative pain scores and the rate of incisional complications.ResultsTreatment groups did not differ in demographic characteristics or baseline heart rate. Percent increase in intraoperative heart rate was significantly larger in cats in the SP group than in the L ( <0.001) and LB groups ( <0.001); the L and LB groups did not differ from each other ( = 0.457). Surgeon-reported unsatisfactory anesthetic depth occurred more frequently in the SP group ( = 2.68,  = 0.044). Surgeon satisfaction with tissue quality, postoperative pain scores and incision complication rates were statistically similar between groups.Conclusions and relevanceThis study is the first to assess the efficacy of local anesthesia for feline castration in an HQHVSN environment, where sustainable operations require delivering humane care with optimal efficiency and resource management. Despite the brief interval between intratesticular anesthetic administration and auto-ligation of the second testicle (median 5 mins, interquartile range 3-7), local anesthesia significantly reduced nociception compared with placebo and did not increase the incidence of incisional complications. These perioperative advantages support incorporating local blocks into multimodal anesthesia and analgesia protocols in HQHVSN clinics.