Alleviation of pain in horses by regional anesthesia/ analgesia techniques, particularly during and following orthopedic surgery, still lags behind developments in human and small animal medicine. After placing continuous peripheral nerve block (CPNB) catheters along the median and ulnar nerves, we determined the antinociceptive efficacy of continuous local anesthetic infusion (CRI). Six medetomidine-sedated horses were instrumented bilaterally under local anesthesia with stainless steel spring-armed CPNB catheters, employing a previously developed ultrasound-(US)-guided technique. Daily US scans were performed. Horses received boluses of 5 (ulnar) to 15 (median) ml per catheter site followed by a CRI of 0,5-2,0 ml/h over 6 days,after which catheters were removed and cultured. While in one forelimb bupivacaine 0,5% [BUP] with vasoconstrictor (i.e. adrenaline 5 μg/ml) was administered along both nerves, in the other limb, serving as control, NaCl 0,9% [SAL] with vasoconstrictor was infused. For daily nociceptive testing, the hoof withdrawal response (HWR) was elicited by stimuli applied to the typical cutaneous areas (TCAs), i.e. skin sites innervated by either the median or ulnar nerve only. Noxious stimuli were either blunt pressure with an algometer (0,2-6,0 kg), a skin pinch in form of a hemostat squeeze, or a 2,5-s constant current impulse train (0,5-10,0 mA, 5 ms, 200 Hz). Stimulus thresholds and HWR latencies were recorded in both forelimbs, and skin pinch responses graded. Data analysis included paired regression analysis. Infusion of BUP (not SAL) increased thresholds and latencies of mechanically and electrically evoked HWRs, and eliminated responses to pinch stimuli (Table). Catheters were well tolerated for 6 days with minor tissue swelling. Of 23 cultured CPNB catheters 17% were contaminated with primarily non-pathogenic, environmental bacteria. In summary, CPNB of the median and ulnar nerves may provide a new method to effectively treat horses suffering during the perioperative period from severe pain originating below the carpus.
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