Local mepivacaine before castration of horses under medetomidine isoflurane balanced anaesthesia is effective to reduce perioperative nociception and cytokine release

Abstract

SummaryBackgroundIn horses castration with primary intention healing is usually performed under balanced inhalation anaesthesia. To optimise analgesia, the use of local anaesthesia was tested.ObjectivesTo investigate the effect of local mepivacaine before castration with first intention healing under balanced medetomidine‐isoflurane anaesthesia and flunixin meglumine, morphine analgesia on perioperative cytokine levels and pain in horses.Study designProspective blinded clinical study.MethodsTwenty stallions were randomly assigned to control or mepivacaine groups. Flunixin meglumine was administered before sedation with medetomidine and followed by ketamine/diazepam intravenously (i.v.). Anaesthesia was maintained with isoflurane and 3.5 μg/kg per hour medetomidine. Mepivacaine horses were given mepivacaine 2% (3.5 mL SC, 1 mL/100 kg intrafunicularly, 2 mL/100 kg intratesticularly) on each side. For recovery, horses were given 2 μg/kg medetomidine i.v. and 0.1 mg/kg morphine i.m. and oral phenylbutazone (0.02 mg/kg q12h) for post‐operative analgesia. One hour before premedication and 4, 8 and 24 h post‐incision, pain was scored with three different pain scales (Equine Utrecht University Scale for Facial Assessment of Pain, Horse Grimace Scale, Equine Utrecht University Scale for Composite Pain Assessment) and plasma cytokines (interleukin‐6 and tumour necrosis factor alpha) were measured. Data were analysed using repeated measures ANOVA, linear regression and unpaired t‐test, significance level P≤0.05.ResultsHorses in both groups showed a significant increase in pain scores and cytokines compared to baseline. Post‐operatively the mepivacaine group exhibited significantly lower pain scores and cytokine levels. Mean heart rate during anaesthesia was significantly lower in the mepivacaine group compared to control group (28.8 ± 1 and 33.2 ± 1.7 respectively). Otherwise there were no differences between the groups.Main limitationsThe decision to provide additional analgesia was based on the attending surgeon's assessment rather than a standardised rescue analgesia plan based on pain scores. The study was only conducted for 24 h post‐castration and complications were not recorded.ConclusionLocal mepivacaine before castration with primary wound closure improved anaesthesia quality, attenuated post‐operative increases in cytokines and reduced post‐operative pain despite balanced anaesthesia with multimodal analgesia in control horses.

BEVA primary care clinical guidelines: Analgesia

“…Four studies confirmed an improvement in surgical quality, with three showing a reduction in anaesthetic agent requirement [25,28,30]. Pain scoring, plasma cortisol or plasma concentrations of inflammatory cytokines (Il-6 and TNFa) were determined in two studies [21,30]. Although there was no difference in cortisol concentrations when lidocaine was used, inflammatory cytokines were lower in animals receiving intratesticular mepivacaine.…”

“…Assessment of pain in the post‐operative period was only established in one study and therefore is the only one to specifically address the question (post‐operative analgesia). One study retained its classification of high quality, two studies were reclassified as moderate quality evidence, two as low quality.…”

“…Twelve studies were identified relevant to the provision of analgesia around castration [19][20][21][22][23][24][25][26][27][28][29][30]. Five studies investigated the use of intratesticular local anaesthesia (lidocaine), of which all were randomised blinded clinical trials and therefore initially graded as providing a high quality of evidence [20,25,27,28,30]. A single study used intratesticular mepivacaine and was also graded as high quality of evidence [30].…”

“…Five studies investigated the use of intratesticular local anaesthesia (lidocaine), of which all were randomised blinded clinical trials and therefore initially graded as providing a high quality of evidence [20,25,27,28,30]. A single study used intratesticular mepivacaine and was also graded as high quality of evidence [30]. Four studies confirmed an improvement in surgical quality, with three showing a reduction in anaesthetic agent requirement [25,28,30].…”

“…Assessment of pain in the post-operative period was only established in one study and therefore is the only one to specifically address the question (postoperative analgesia). One study [30] retained its classification of high quality, two studies were reclassified as moderate quality evidence, two as low quality. The effect of systemic analgesia was investigated in seven studies, but most assessed a single agent and did not attempt to identify the superiority/inferiority of any particular agent.…”