Nerve Stimulator-Guided Ciatic and Femoral Nerve Block during Tibial Osteosynthesis in Chinchilla lanigera

Abstract

Background: Nociceptive stimulation in orthopedic surgery requires effective pain management to ensure trans and postoperative patient comfort. Several techniques can be used for this, and multimodal analgesia protocols such as guided locoregional blocks provide a balanced effect, as they enable the use of low-dose anesthetics and offer rapid recovery. The benefits of specific nerve blocks in domestic animals are well known; however, there are few reports that have ascertained their safety in wild species. This report is aimed at describing the successful use of neurolocalizer-guided sciatic and femoral nerve blocks during tibial osteosyntheses in a chinchilla.

Case: A 9-month-old chinchilla weighing 0.56 kg was referred for surgery for proximal and mid-diaphyseal tibia fractures resulting from trauma. Following preanesthetic evaluation, the animal received intramuscular dexmedetomidine (15 µg kg^-1) as preanesthetic medication. Sedation was apparent after 15 min and was verified by a decreased activity, the animal allowing manipulation, absence of the eyelid and righting reflexes, and limb movement after clamping removal of limb after clamping. After achieving sedation, anesthesia was induced and maintained with sevoflurane (FiO2 = 1.0), supplied through a nasoral mask. Sciatic and femoral nerve blocks were performed with the aid of a neurostimulator. A needle was inserted into the femoral triangle, cranial to the femoral artery, and into the depression between the sciatic tuberosity and the greater femoral trochanter. The neurostimulator was set at a pulse frequency of 1 Hz, pulse duration of 0.1 ms and initial current of 0.6 mA. The needle was advanced toward the nerves until muscle contractions were observed, and the current was gradually reduced until contractions were manifested at a minimum current of 0.2 mA. Ropivacaine 0.2% (1 mg kg^-1) was injected at each point. Intraoperative physiological parameters remained stable and within the reference limits while the animal was under light anesthesia. Signs of recovery appeared soon after the inhaled anesthesia was stopped; awakening was gradual and without any signs of excitement or other adverse effects, eliminating the need for additional analgesic medication. Subcutaneous fluid therapy, antibiotics, and anti-inflammatory medications were administered immediately postoperatively.

Discussion: This report is groundbreaking in describing neurostimulation-guided sciatic and femoral nerve blocks as an alternative to epidural anesthesia for hind limb surgery; furthermore, it demonstrates the efficacy and safety of ropivacaine in Chinchilla lanigera, which is relevant to the clinical use of the drug as part of a rodent anesthetic protocol. Sevoflurane associated dexmedetomidine use and locoregional anesthesia resulted in cardiorespiratory stability and the absence of behavioral signs of pain in the immediate postoperative period. The technique was easy to apply, and the use of the neurolocalizer increased blockade safety by allowing anesthesia administration as close as possible to the nerve. The ability to use low doses is a significant benefit in patients with low body weights. Therefore, the chosen protocol resulted in a safe and balanced anesthesia with an effective regional block that provided trans and postoperative analgesia and allowed rapid recovery for chinchilla tibial osteosynthesis.