Skills Laboratory: How to perform four oral regional nerve blocks in dogs and cats

Nerve blocks are an essential component of a high-quality dentistry service in small-animal practice. Nerve blocks 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 regional nerve blocks to their patients undergoing oral surgery. 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 to provide regional analgesia 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.

Click on the titles below to access step-by-step pictorial guides to each of these blocks:

• Rostral maxillary (infraorbital) regional block

• Caudal maxillary (maxillary) regional block

• Rostral mandibular (middle mental) regional block

• Caudal mandibular (inferior alveolar) regional block

Also, click here to view a video of all four techniques.

REFERENCES

1. Holmstrom SE, Frost P, Eisner ER. Regional and local anesthesia. In: Veterinary dental techniques. 2nd ed. Philadelphia, Pa: WB Saunders, 2007;626.

2. Mama KR. Local anesthetics. In: Gaynor JS, Muir WW, eds. Handbook of veterinary pain management. St. Louis, Mo: Mosby, 2002;232.

3. Beckman BW. Pathophysiology and management of surgical and chronic oral pain in dogs and cats. J Vet Dent 2006;23(1):50-60.