The influence of a continuous rate infusion of dexmedetomidine on the nociceptive withdrawal reflex and temporal summation during isoflurane anaesthesia in dogs

Abstract

ObjectiveTo examine the influence of a low dose dexmedetomidine infusion on the nociceptive withdrawal reflex and temporal summation in dogs during isoflurane anaesthesia. Study designProspective experimental blinded cross-over study. AnimalsEight healthy mixed breed dogs, body weight Mean ± SD 26.5 ± 8.4 kg and age 25 ± 16 months. MethodsAnaesthesia was induced with propofol and maintained with isoflurane (Fe′ISO 1.3%) delivered in oxygen and air. After stabilization, baseline recordings (time 0) were obtained, then a dexmedetomidine bolus (1 μg kg−1 IV) followed by a continuous rate infusion (1 μg kg−1 hour−1) or saline placebo were administered. At times 10, 30 and 60 minutes after the initial bolus, electrical stimulations of increasing intensity were applied over the lateral plantar digital nerve, and administered both as single and as repeated stimuli. The resulting reflex responses were recorded using electromyography. Data were analysed using a multivariable linear regression model and a Kruskal Wallis test for single stimulation data, and repeated measures anova and paired t-test for repeated stimulation data. ResultsThe AUC for the stimulus-response curves after single stimulation were similar for both treatments at time 0. At times 10, 30 and 60 the AUCs for the stimulus-response curves were significantly lower with dexmedetomidine treatment than with placebo. Temporal summation was evident in both treatments at times 0, 10, 30 and 60 starting from a stimulation intensity of 10 mA. The magnitude of temporal summation was smaller in dexmedetomidine than in placebo treated dogs at time 10, 30 and 60, but not at time 0. ConclusionsDuring isoflurane anaesthesia, low dose dexmedetomidine suppresses the nociceptive reflex responses after single and repeated electrical stimulation. Clinical relevanceThis experimental study confirms previous reports on its peri-operative efficacy under clinical conditions, and further indicates that dexmedetomidine might reduce the risk of post-operative chronic pain development.