Maxillary nerve block

Local anesthetics are used as part of the anesthetic regimen to decrease the nociceptive input into the central nerve system (CNS) and therefore reduce the amount of the general anesthesia needed. Maxillary or infraorbital nerve blocks are recommended during clefts repair.

An intra- or extraoral approach is used to block the maxillary nerve before CP and CLP repair.

The roof of the mouth is formed by the incisive, maxillary and palatine bones. At the level of maxillary canine teeth there are two large openings – palatine fissures. The caudal aspect of the hard palate merges with the soft palate just caudal to the maxillary second molar teeth. The caudal aspect of the soft palate ends just at the tip of the epiglottis. Soft palate is formed by two mucosal surfaces, nasal and oral, respectively, and a muscular layer in-between.

The blood supply to the hard palate is provided by paired major palatine arteries. This artery emerges from the palatine canal through the major palatine foramen at the level of the distal aspect of maxillary fourth premolar tooth on each side. It courses rostrally in the palatine groove, which is located midway between the teeth and the midline of the palate. Blood vessels are accompanied with nerves which innervate the hard palate and regional soft tissues. Hard palate is innervated by the branches deriving from the maxillary branch of the trigeminal nerve (V). Blood supply to the soft palate includes small vessels only. Soft palate is innervated by branches of the trigeminal nerve (V), glossopharyngeal nerve (IX) and vagus (X).

The notch between the caudal border of the cranial ventral aspect of the zygomatic arch and the maxilla is palpated. The needle is advanced from this point parallel to the plane of the hard palate and slightly rostrally to touch the palatine bone. Then the needle is retracted 2-3 mm. Aspiration and injection are performed.

The needle is passed dorsally either through the conjunctiva or through the skin close to the lateral canthus of the eye. The needle is advanced a short distance ventrally at a right angle to the axis of the hard palate.

The short 27G needle is passed behind the second molar tooth at a 90˚ angle with the palate. A curved needle is sometimes used to try placing the needle's tip closer to the entrance of the infraorbital canal. The local anesthetic solution volume varies depending on the size of the animal and dose maximum of the local anesthetic drug chosen.

Major palatine foramen approach to the maxillary nerve is rarely recommended because this technique can result in trauma to the major palatine artery with subsequent severe hemorrhage.