Peripheral nerve blocks are performed by injecting local anesthetic in the immediate vicinity of a peripheral nerve or nerve plexus. Common peripheral nerve blocks in small animal patients include epidural, brachial plexus, forefoot, intraarticular stifle, and dental blocks. All but dental peripheral nerve blocks were covered in the March 2004 issue, pages 47-50.
Local anesthetic blocks can be given to heavily sedated or anesthetized animals. Greatest efficacy is obtained when they are given before surgery is begun. Effective peripheral nerve blocks provide excellent anesthesia and analgesia and can reduce the amount of inhalation anesthetic needed to perform a procedure as well as mitigate the "wind-up" response of the CNS to noxious stimuli.
The duration of effect varies with the type of local anesthetic. (See March, page 47, for further information about specific local anesthetic agents and tips about their use.) Shorter-acting agents provide 1 hour of anesthesia, and longer-acting agents provide up to 6 hours. The duration of analgesia, or reduced sensation of pain, may be longer.
Opioid analgesics, such as morphine, can be administered locally along with lidocaine or bupivacaine to augment the duration of analgesia. In addition to the CNS, opioid receptors are present in the periphery if tissues are inflamed.
Applications & Necessities
Sensory nerve fibers that innervate the bone, teeth, and soft tissues of the oral cavity emanate from the maxillary or mandibular branches of the trigeminal nerve. Four regional nerve blocks can be readily performed to provide analgesia for dental and oral surgical procedures.
- Tuberculin syringe
- 25- to 27-gauge, 3/4- to 1-inch needle
Drugs and Dosages
- Bupivacaine 0.5%: 0.1 to 0.5 ml per site for dogs and 0.1 to 0.3 ml for cats. An additional 50% of the agent can be administered for an infraorbital nerve block. The peak effect occurs within 30 minutes and the duration is 4 to 6 hours.
- Do not exceed a maximum cumulative dose of 2.0 mg/kg.
Mental Nerve Block