RESUMEN
BACKGROUND: Surgery of the goat stifle joint requires good perioperative analgesia, ideally without affecting motor function in the postoperative period. The objective of this study was to describe an ultrasound-guided technique for saphenous nerve block in goats. Eleven fresh female goat cadavers from two different age groups were used: seven of them were four years old with a mean ± SD body weight of 65.9 ± 7.3 kg. Four animals were six months old and their mean ± SD body weight was 20.1 ± 3.1 kg. The cadavers were positioned in lateral recumbency with the limb to be blocked lowermost. A high-frequency linear transducer (6-12 MHz) was used to localise the interfascial plane between the sartorius and the vastus medialis muscles and to identify the saphenous nerve on the medial aspect of the thigh, caudal to the femur, at the level of the femoral triangle. In 22 pelvic limbs 0.1 mL/kg of methylene blue was injected around the saphenous nerve under ultrasound guidance, followed by gross anatomical dissection. The length of circumferentially stained nerve was measured, and the success rate of achieving at least 1 cm of staining is presented with a 95% confidence interval (CI). RESULTS: Although not all saphenous nerves were sonographically identified, their boundaries were defined as cranial to the femoral artery, lateral to the sartorius muscle, and medial to the vastus medialis and rectus femoris muscles, within the perivascular fat. During anatomical dissection, the overall dye solution distribution was graded as complete in 17/22 limbs indicating a 77.3% success rate [95% CI (0.598, 0.948)], partial in 3/22 limbs and failed in 2/22 limbs. CONCLUSIONS: The success rate of this study indicates the feasibility of employing the ultrasound-guided technique to perform saphenous nerve block in goats. However, further in-vivo studies are recommended to assess the block's clinical efficacy before implementation on clinical patients.
RESUMEN
BACKGROUND: Epidural administration of local anaesthetic agents provides good intraoperative antinociception for orthopaedic procedures of the pelvis and the pelvic limb. However, in cats the spinal cord extends approximately to the level of the first sacrococcygeal vertebra, and therefore the sacrococcygeal epidural could be a safer alternative to the lumbosacral epidural in cats. This case series describes perioperative analgesia and the haemodynamic status of seven client-owned cats that received sacrococcygeal epidural injection of 0.5% bupivacaine and underwent orthopaedic hind leg or pelvic surgeries under general anaesthesia. CASE PRESENTATION: Each cat received either 0.2 or 0.3 mL/kg of 0.5% bupivacaine with or without 0.2 mg/kg of morphine in the sacrococcygeal epidural space. Intraoperative antinociceptive response to surgical stimulus and haemodynamic changes were monitored and reported. CONCLUSION: In these seven anaesthetised cats, 0.2 or 0.3 mL/kg of 0.5% bupivacaine, administered alone or in combination with morphine into the sacrococcygeal epidural space, enhanced antinociception so that intraoperative rescue analgesia was unnecessary in all but one cat. It also reduced the anticipated requirement for postoperative opioid use. However, a high incidence of hypotension was observed in the cats in this report, and hence intraoperative blood pressure monitoring should be considered mandatory in anaesthetised cats following epidural injection of local anaesthetic agents, regardless of injection site.