Is a Block of the Femoral and Sciatic Nerves an Alternative to Epidural Analgesia in Sheep Undergoing Orthopaedic Hind Limb Surgery? A Prospective, Randomized, Double Blinded Experimental Trial

SIMPLE SUMMARY: Many human diseases are not yet fully understood. Tests in animals can support the evaluation of new techniques meant to be applied in humans. Such animal experiments can only be justified with continuous improvements of the analgesic protocols during and after surgery. This study was designed to test the efficacy and feasibility of a technique aiming to desensitize the large nerves of one hind limb in experimental sheep undergoing invasive surgery on one hind limb. This technique was compared to epidural analgesia, a technique known to be effective in alleviating pain but leading to stress due to an inability to move both hind limbs in the early post-operative phase. Nerve blocks of peripheral nerves are widely used in human and veterinary medicine and can improve peri-operative pain therapy. The following study demonstrated that peripheral nerve block provided comparable analgesia to epidural anesthesia. Peripheral nerve blocks of the sciatic and femoral nerves can be used as an alternative to epidural analgesia in experimental sheep. ABSTRACT: Peripheral nerve blocks are commonly used in human and veterinary medicine. The aim of the study was to compare the analgesic efficacy of a combined block of the femoral and sciatic nerves with an epidural injection of ropivacaine in experimental sheep undergoing orthopaedic hind limb surgery. Twenty-five sheep were assigned to two groups (peripheral nerve block; sciatic and femoral nerves (P); epidural analgesia (E)). In group P 10 mL ropivacaine 0.5% was injected around the sciatic and the femoral nerves under sonographic guidance and 10 mL NaCl 0.9% into the epidural space while in group E 10 mL ropivacaine 0.5% was injected into the epidural space and 10 mL NaCl 0.9% to the sciatic and the femoral nerves. During surgery, heart rate, respiratory rate and mean blood pressure were used as indicators of nociception. In the postoperative phase, nociception was evaluated every hour by use of a purposefully adapted pain score until the animal showed painful sensation at the surgical site. The mean duration of analgesia at the surgical wound was 6 h in group P and 8 h in group E. Mean time to standing was 4 h in group P and 7 h in group E. In conclusion time to standing was significantly shorter in group P while the duration of nociception was comparable in both groups. The peripheral nerve block can be used as an alternative to epidural analgesia in experimental sheep.