Dental Nerve Blocks in Dogs and Cats Enhance Anesthesia Safety
Gero December 6, 2019
The Video Above Demonstrates Oral
Regional Nerve Blocks in Dogs and Cats
Please Click the Video to Watch Now &
Sign up for Free Online Dentistry Training
Dental nerve blocks in dogs and cats provide a quick and easy pain management technique to decrease the amount of inhalant anesthetic needed during oral surgery and enhance postoperative patient comfort.
Dental nerve block in dogs and cats are an essential component of a high-quality dentistry service in small-animal practice. Nerve blocks in dogs and cats not only provide excellent postoperative analgesia but also contribute extensively to maximizing the safety of the anesthetic event. This is accomplished by the resulting sodium channel neuronal blockade, which minimizes the required concentration of the inhalant anesthetic. Lower inhalant concentrations allow cardiac output, respiration rate, blood pressure, tissue oxygenation, and tissue perfusion to remain optimal.1 Veterinary dentistry commonly involves small patients and long procedures, so maintaining normothermia with optimal perfusion is also essential and is enhanced by using lower inhalant anesthetic concentrations.
Equipment
Most practices likely have everything available to deliver dental nerve blocks to dogs and cats undergoing oral surgery in their practice.. A tuberculin syringe with a 5/8-in 25-ga needle is used for patients up to 8.8 lb (4 kg). For patients over 8.8 lb, 3- or 6-ml syringes with 3/4-in 22- to 25-ga needles are used, depending on the infusion volume needed. Smaller-gauge needles minimize the feel of the needle in the tissue and make correct placement confirmation difficult.
Agents
Lidocaine (2%) and bupivacaine (0.5%) can be used in the same syringe. The quick onset of lidocaine and the long duration of bupivacaine provide obvious dual benefit.2 The maximum recommended total dose for these agents is 1 mg/kg of each in the mixture. The proper dose can be drawn by using 0.2 ml of 2% lidocaine and 0.8 ml of 0.5% bupivacaine per 10 lb body weight.
Volume per site
The maximum recommended volume of the lidocaine-bupivacaine mixture to be injected per site is based on the size of the patient as follows3:
- Cat or small dog (< 13.2 lb [6 kg]) = 0.1 to 0.3 ml
- Medium-sized dog (13.2 to 55 lb [6 to 25 kg]) = 0.3 to 0.6 ml
- Large dog (55.1 to 88 lb [25.1 to 40 kg]) = 0.8 to 1.2 ml
- Extra-large dog (> 88 lb [40 kg]) = 1.4 to 1.6 ml
Common blocks
Four nerve blocks are commonly used for dental nerve blocks in dogs and cast to the different regions of the oral cavity of mesocephalic and dolicocephalic dogs—the infraorbital and maxillary and the middle mental and inferior alveolar. Only three of these nerve blocks are performed in cats and brachycephalic dogs because the extremely short infraorbital foramen in these patients allows the infraorbital approach to affect the entire maxilla on the corresponding side. Therefore, this precludes the need for a separate maxillary nerve block in these patients.
For each of these blocks, once the correct dose of the desired local anesthetic agent is drawn and the needle is advanced to the desired location, the agent is placed after aspiration to ensure that the needle is not in a vessel. Avoid advancing or retracting the needle while injecting to avoid inadvertent vessel entry.
Step-by-step pictorial guides to each of these blocks:
Rostral maxillary (infraorbital) regional block
This block affects the infraorbital nerve and the rostral maxillary alveolar nerve. It provides analgesia to the incisors, canine, and first three premolar teeth of the corresponding side. The adjacent maxillary bone and surrounding soft tissue are also affected.
Step 1
Use a skull to identify the infraorbital foramen just mesial to the mesiobuccal root of the maxillary fourth premolar. The needle is shown passing through the foramen and into the infraorbital canal.
Step 2A
To perform the infraorbital nerve block in dogs, retract the upper lip dorsally, and palpate the infraorbital foramen.
Step 2B
Also, palpate the infraorbital neurovascular bundle as it exits the infraorbital canal and courses rostrodorsally. The circle represents the infraorbital foramen, and the arrow demonstrates the course and direction of the corresponding neurovascular bundle.
Step 3
With the lip and the bundle retracted dorsally with one hand, use the opposite hand to advance the needle close to the maxillary bone ventral to the retracted bundle in a caudal direction to a point just inside the canal. The needle should pass into the canal without hitting bone. If bone is encountered, withdraw the needle slightly, and redirect it to pass easily into the canal.
Caudal maxillary (maxillary) regional block
This block affects the branches of the maxillary nerve—the infraorbital nerve, the pterygopalatine nerve, and the major and minor palatine nerves.1 Structures that are blocked include the bones, teeth, and soft tissues of the upper jaw, including the bones of the hard palate and the soft and hard palatal mucosa on the corresponding side.
Step 1
Use a skull to visualize the needle placement caudal to the maxillary second molar.
Reference
- Beckman BW, Legendre L. Regional nerve blocks for oral surgery in companion animals. Compend Contin Ed Pract Vet 2002;24:439-444.
Step 2
To perform the maxillary block, open the patient’s mouth, and retract the lip commissure caudally.
Step 3
Advance the needle in a dorsal direction perpendicular to the plane of the palate, penetrating the mucosa directly behind the palatal and distobuccal roots of the maxillary second molar tooth. The needle does not need to be advanced more than 3 to 5 mm beyond the mucosa, depending on the patient’s size.
Rostral mandibular (middle mental) regional block
This dental nerve block in dog affects the incisors and canine tooth of the corresponding side along with the adjacent bone and soft tissues.
Step 1
Use a skull to familiarize yourself with the middle mental foramen. The needle is shown passing through the middle mental foramen into the mandibular canal.
Step 2
To perform the middle mental nerve block in dogs, retract the mandibular labial frenulum ventrally with one hand.
Step 3
With the other hand, guide the needle in a caudal and slightly ventral direction, passing into the middle mental foramen that exists one-third of the distance from the ventral border of the mandible. In dogs, this foramen is at the level of the mesial root of the second premolar. In cats, it lies halfway between the canine tooth and the third premolar.
Caudal mandibular (inferior alveolar) regional block
This block affects all mandibular teeth, mandibular bone, and soft tissue on the corresponding side rostral to the injection site.
Step 1
Use a skull to identify the inferior alveolar nerve (short white arrow), the angular process of the mandible (yellow arrow), and the location of the intended needle placement (long white arrow). The inferior alveolar nerve is blocked before its entry into the mandibular canal.
Step 2
The inferior alveolar block is performed extraorally by first palpating the indentation on the ventral border of the caudal mandible just rostral to the angular process. This indentation should be at the same rostral-to-caudal plane as the lateral canthus of the eye. So if the indentation is difficult to palpate, the lateral canthus of the eye can be used as a landmark.
Step 3
Pass the needle into the skin on the lingual aspect of the caudal extent of the indentation. With the needle parallel to the lingual aspect of the mandible, advance it along the bone until it reaches one-third of the distance from the ventral to the dorsal mandibular body. The needle will now be in the vicinity of the mandibular foramen where the inferior alveolar nerve enters the mandibular canal.
References
Holmstrom SE, Frost P, Eisner ER. Regional and local anesthesia. In: Veterinary dental techniques. 2nd ed. Philadelphia, Pa: WB Saunders, 2007;626.
Mama KR. Local anesthetics. In: Gaynor JS, Muir WW, eds. Handbook of veterinary pain management. St. Louis, Mo: Mosby, 2002;232.
Beckman BW. Pathophysiology and management of surgical and chronic oral pain in dogs and cats. J Vet Dent 2006;23(1):50-60.