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Nerve blocks are essential before oral surgical procedures are performed in dogs.
Not only do nerve blocks provide a basis for pain management in the immediate postoperative period, they also allow for decreased minimum alveolar concentration of inhalant anesthetic, resulting in a safer procedure.
The maximum dose of bupivacaine is determined by patient weight; a safe target maximum dose is 2 mg/kg.1 The volume range of anesthetic infused per site based on patient weight varies (Table, below).
Types of Nerve Blocks
Several types of nerve blocks can be used in oral surgery:
Rostral maxillary(infraorbital)blocks affect bone, teeth, and intraoral soft tissue from the maxillary third premolar rostral to the midline.
Caudal maxillaryblocks affect bone, teeth, and intraoral soft tissue from the last molar rostral to the midline, including the ipsilateral soft and hard palatal mucosa and bone.
Rostral mandibular(mental) blocks affect bone, teeth, and intraoral soft tissue from the mandibular second to third premolar rostral to the midline.
Caudal mandibular (inferior alveolar) blocks affect bone, teeth, and intraoral soft tissue from the mandibular third molar rostral to the midline.
Care should always be taken not to inject a vessel. Although rare, resistance when depressing the syringe plunger indicates that the needle may be in the nerve; the needle should be withdrawn and redirected. Extravascular placement can be ensured by aspirating the needle before injection.
0.5% Bupivacaine Infusion Volume per Site Based on Patient Weight
Patient Weight (kg)
Volume Range (mL)
≤6
0.1–0.3
6–25
0.3–0.6
25–40
0.7–1
>40
1.1–1.4
Presurgical Considerations
Exact placement of the anesthetic agent is not required. Extravasation of the agent throughout the tissue allows minor deviations in needle placement. However, the more accurate the placement of medication, the less agent required to achieve effect. A canine skull is convenient to have on hand for reviewing anatomic landmarks.
Keeping the patient at a light anesthetic plane can enhance safety and allow the surgeon to confirm effectiveness of the nerve block. If the block was not performed correctly or if the full anesthetic effect has not been achieved, the patient will physiologically react to the initial surgical incision.
Provided the volume of bupivacaine administered is within the maximum recommended volume for the patient’s weight, additional agents can be administered if a particular block is ineffective.
Small- to medium-sized brachycephalic patients do not require a caudal maxillary block. Their short infraorbital canals allow the agent to be placed via the rostral maxillary block to reach nerves before entry into the infraorbital foramen and maxillary bone.
To assist with needle placement, visualize the infraorbital foramen that lies dorsal to the distal root of the maxillary third premolar.
Author Insight
Confirm needle placement in the canal before injecting anesthetic. The needle should pass freely into the canal without meeting bony resistance. When correctly placed, the needle will encounter resistance with gentle lateral movement rather than freely moving beneath adjacent alveolar mucosa.
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Step 2
Retract the upper lip dorsally to expose the infraorbital neurovascular bundle (arrow) that courses rostral and dorsal from the foramen terminus. This structure can easily be palpated in most canine patients. Advance the needle just rostral to the foramen opening parallel and adjacent to the maxillary bone in a rostral-to-caudal direction. The needle should rest just inside the canal.
Step 1
To assist with needle placement, visualize the infraorbital foramen that lies dorsal to the distal root of the maxillary third premolar.
Author Insight
Confirm needle placement in the canal before injecting anesthetic. The needle should pass freely into the canal without meeting bony resistance. When correctly placed, the needle will encounter resistance with gentle lateral movement rather than freely moving beneath adjacent alveolar mucosa.
Step 2
Retract the upper lip dorsally to expose the infraorbital neurovascular bundle (arrow) that courses rostral and dorsal from the foramen terminus. This structure can easily be palpated in most canine patients. Advance the needle just rostral to the foramen opening parallel and adjacent to the maxillary bone in a rostral-to-caudal direction. The needle should rest just inside the canal.
Step-by-Step: Caudal Maxillary Nerve Block
1 of 2
Step 1
To assist with needle placement, visualize the ledge of bone just caudal to the second maxillary molar.
2 of 2
Step 2
Insert the needle in a ventral-to-dorsal direction into the soft palatal mucosa where it meets the bone, just caudal to the second mandibular molar. Advance the needle no more than 3–5 mm, depending on patient size, to ensure the tip rests directly under the nerves just before the nerves enter the maxillary bone and infraorbital foramen rostrally.
Step 1
To assist with needle placement, visualize the ledge of bone just caudal to the second maxillary molar.
Step 2
Insert the needle in a ventral-to-dorsal direction into the soft palatal mucosa where it meets the bone, just caudal to the second mandibular molar. Advance the needle no more than 3–5 mm, depending on patient size, to ensure the tip rests directly under the nerves just before the nerves enter the maxillary bone and infraorbital foramen rostrally.
To assist with needle placement, visualize the notch in the caudal ventral mandibular body rostral to the angular process. An alternative landmark is the lateral canthus of the eye (arrow, Step 2). Dropping an imaginary line directly ventral from the lateral canthus to the ventral mandible allows similar needle placement.
Author Insight
The caudal mandibular block can be administered intraorally; however, it is more technically difficult.
2 of 3
Step 1 (vestibular [lateral] view)
To assist with needle placement, visualize the notch in the caudal ventral mandibular body rostral to the angular process. An alternative landmark is the lateral canthus of the eye (arrow, Step 2). Dropping an imaginary line directly ventral from the lateral canthus to the ventral mandible allows similar needle placement.
Author Insight
The caudal mandibular block can be administered intraorally; however, it is more technically difficult.
3 of 3
Step 2
Palpate the notch, then direct the needle through the skin toward the lingual aspect of the mandibular body at a 20- to 40-degree angle. Palpation allows tactile confirmation that the tip contacts the bone; the tip should rest just ventral to where the inferior alveolar nerve enters the mandibular canal.
Step 1 (lingual view)
To assist with needle placement, visualize the notch in the caudal ventral mandibular body rostral to the angular process. An alternative landmark is the lateral canthus of the eye (arrow, Step 2). Dropping an imaginary line directly ventral from the lateral canthus to the ventral mandible allows similar needle placement.
Author Insight
The caudal mandibular block can be administered intraorally; however, it is more technically difficult.
Step 1 (vestibular [lateral] view)
To assist with needle placement, visualize the notch in the caudal ventral mandibular body rostral to the angular process. An alternative landmark is the lateral canthus of the eye (arrow, Step 2). Dropping an imaginary line directly ventral from the lateral canthus to the ventral mandible allows similar needle placement.
Author Insight
The caudal mandibular block can be administered intraorally; however, it is more technically difficult.
Step 2
Palpate the notch, then direct the needle through the skin toward the lingual aspect of the mandibular body at a 20- to 40-degree angle. Palpation allows tactile confirmation that the tip contacts the bone; the tip should rest just ventral to where the inferior alveolar nerve enters the mandibular canal.
References
References
Management of postoperative and other acute pain. Dobromylskyj P, Flecknell PA, Lascelles BDX, et al. In Flecknell PA, Waterman-Pearson AE (eds): Pain Management in Animals, 1st ed—London: Saunders Elsevier, 2000, p 113.
Suggested Reading
Anesthesia and pain management for small animals. Beckman BW. Vet Clin North Am Small Anim Pract 43:669-688, 2013.
Handbook of Veterinary Pain Management, 2nd ed. Gaynor JS, Muir III WW—St. Louis: Mosby Elsevier, 2009.
Pathophysiology and management of surgical and chronic oral pain in dogs and cats. Beckman BW. J Vet Dent 23:50-60, 2006.
Author Information
For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.
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