In the January and March issues of Veterinary Medicine, we discussed several local and regional anesthetic techniques to help in the analgesic management of patients. This article
discusses techniques associated with oral surgery—blocking the infraorbital and maxillary nerves in the maxilla and the mental
and mandibular (inferior alveolar) nerves in the mandible. Appropriately applied nerve blocks can reduce nociceptive input,
thereby facilitating preemptive and multimodal analgesia and potentially reducing a patient's inhalant anesthetic and postoperative
analgesic requirements. Look for the final part of this series, which will cover epidural anesthesia and analgesia, later
this year.
INDICATIONS AND COMPLICATIONS
Table 1: Indications and Drug Dosages for Infraorbital, Maxillary, Mental, and Mandibular (Inferior Alveolar) Nerve Blocks
in Dogs and Cats. Note: In the Dosages column, the drug doses are the total maximum dose, to be divided among all injection sites.
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The trigeminal nerve and ganglion carry nociceptive input from the head to the brainstem. The trigeminal nerve has three branches:
ophthalmic, maxillary, and mandibular. Infraorbital, maxillary, mental, and mandibular (inferior alveolar) nerve blocks provide
anesthesia to the upper or lower jaw and are commonly performed in practice for dental extractions. These blocks are also
used for any surgical procedure of the upper or lower jaw (Table 1).
These blocks can be difficult to perform in obese and brachycephalic animals because the landmarks are more challenging to
palpate. Possible complications of infraorbital, maxillary, mental, and mandibular (inferior alveolar) blocks include trauma
to the nerve, resulting in neurapraxia, and inadvertent intravenous or intra-arterial injection of local anesthetic; retrobulbar
hemorrhage could occur with the infraorbital block. As for all local and regional anesthesia techniques, aspiration before
injection is imperative to avoid intravenous or intra-arterial injection.
DRUGS AND PREPARATION
The local anesthetics used most commonly in these blocks are 2% lidocaine, 0.5% bupivacaine, or a combination of both (Table 1). Onset of anesthesia with 2% lidocaine occurs in five to 10 minutes and lasts for about one to one-and-a-half hours. The
duration of anesthesia can be extended up to two hours by adding epinephrine to the lidocaine (0.1 ml of 1:1,000 [0.1 mg]
epinephrine per 20 ml of local anesthetic). Onset of anesthesia with bupivacaine occurs in 20 to 30 minutes and lasts for
about four to six hours. The combination of lidocaine and bupivacaine results in a more rapid onset but may reduce the duration
of anesthesia. Adding an opioid increases the efficacy and prolongs the duration of analgesia with the blocks.
With these blocks, the needle is usually inserted percutaneously, but the infraorbital and mental blocks may be performed
through the oral mucosa, depending on patient anatomy. Sterile preparation of the area is not usually performed, but a sterile
needle and syringe must be used.
INFRAORBITAL AND MAXILLARY NERVE BLOCKS
1. The position of the needles to block the maxillary nerve in dogs and cats. Local anesthetic administration at the infraorbital
foramen (A) will provide anesthesia rostral to the foramen. Local anesthetic administration where the maxillary nerve courses
perpendicular to the palatine bone, between the maxillary foramen and the foramen rotundum (B), will provide anesthesia to
the entire upper jaw, including the teeth, on one side.
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Blocking the infraorbital nerve, the continuation of the maxillary nerve, as it exits the infraorbital foramen (Figure 1, A) anesthetizes the upper lip, nose, roof of the nasal cavity, and skin as far caudal as the infraorbital foramen. The maxillary
incisors are inconsistently blocked with this technique, particularly in dogs.1-3
This block should be performed cautiously in brachycephalic dogs and cats (e.g. Himalayans, Persians) because of the proximity of the orbit to the foramen and the potential for penetrating the globe. Retrobulbar
hemorrhage leading to proptosis is a potential complication of this technique.
To desensitize the infraorbital branch of the maxillary nerve at its point of emergence from the infraorbital foramen, insert
a 25- to 29-ga needle, either percutaneously or through the buccal mucosa, into the foramen, which is usually found dorsal
to the third premolar, and advance it 1 to 2 mm. Elevate the head, aspirate before injection, and apply digital pressure over
the foramen as you slowly inject the local anesthetic to facilitate its movement caudally into the foramen, causing more effective
nerve blockade. Advancing the needle farther into the foramen is not recommended because this increases the chance of lacerating
the nerve.
To anesthetize the entire upper jaw, including all of the teeth, block the maxillary nerve where it courses perpendicular
to the palatine bone, between the maxillary foramen and the foramen rotundum (Figure 1, B).2,3 Insert the needle through the skin at a 90-degree angle, in a medial direction, ventral to the border of the zygomatic arch
and about 0.5 cm caudal to the lateral canthus, and then advance it toward the pterygopalatine fossa. Frequently, the needle
will contact the ramus of the mandible; if you do so, walk it off the ramus cranially. Slowly inject the local anesthetic
after test aspiration. This technique is more difficult to perform in cats.
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