5 Local Anesthesia
When you have completed this chapter, you will be able to:
• List possible reactions to local anesthetics used in veterinary dentistry.
• Describe the use of bupivacaine in veterinary dentistry and list time of onset of activity and duration of action for this drug.
• State maximum volumes of local anesthetics that should be administered to dogs and cats.
• Describe the purpose and procedure for performing an infiltration block.
• Describe the purpose and procedure for performing a regional anesthetic block.
• List the four anatomic areas where regional anesthesia is performed before veterinary dental procedures.
For a good understanding of general anesthesia and pain management, the reader is encouraged to read Thomas: Anesthesia and Analgesia for Veterinary Technicians. This chapter is devoted to local anesthesia, which is used in veterinary dentistry to reduce the depth of general anesthesia that is needed and to control pain after the procedure. This can minimize complications of general anesthesia such as hypoventilation, hypotension, and bradycardia.
State law will vary from state to state as to the legality of the technician performing these procedures. In addition, it is up to the supervising veterinarian to prescribe and determine the appropriateness of the technician performing the procedure.
Bupivacaine is the drug of choice at a 0.5% solution or 5 mg/ml. In the author’s opinion, bupivacaine requires approximately 4 to 8 minutes for onset of action and the duration of action is 6 to 10 hours. Bupivacaine may be used with or without epinephrine (adrenaline), which may decrease the chance of toxicity.
Possible but rare reactions to local anesthetics include toxicity to skeletal muscle, anaphylactic reactions, and permanent nerve damage. A simple rule of thumb to avoid toxicity is to never exceed 2.0 mg/kg in cats and dogs. Exercise care, especially in smaller patients and cats, so that these maximum doses are not exceeded. The maximum number of sites would be four if the patient requires surgical manipulation in all four quadrants (left and right maxillary and left and right mandibular). Generally, the patient should receive the following at each site: Cats and small dogs = 0.1 ml, medium dogs = 0.2 ml, and large dogs = 0.3 ml. The total volume used depends on the size of the patient and the number of sites that require analgesia. For example, if regional anesthesia is being performed and all four quadrants were blocked in a 10 lb (4.6 kg) cat, the cat would receive 0.4 ml or 2.0 mg, well below the maximum dose of 9.2 mg. Other factors, such as inflammation that causes a reduction of the pH of inflamed tissue, will render local anesthetics less effective.
After administration of the block, the patient should be evaluated for the effectiveness of the block. If respiration rate, heart rate, and blood pressure increase with surgical manipulation, the block either has not had time for onset or was not correctly placed. If the block is not effective and enough time as elapsed, the block may be repeated as long as the maximum total dose is not exceeded. There are two types of local anesthesia: Infiltration blocks and regional anesthesia.
Infiltration Blocks
Infiltration blocks are the least effective method of local anesthesia and are used only after the procedure in an attempt to reduce postoperative discomfort. Rather than blocking an entire quadrant, they block only the area where the infiltration has been administered.
Equipment
A 25- or 27-gauge needle and a disposable syringe (Figure 5-1, A) are needed. Alternatively, a dental local anesthesia syringe can be used (Figure 5-1, B).
Regional Blocks
The advantage of regional anesthesia is the ability to block entire quadrants. The disadvantages of regional nerve blocks include transient loss of sensation and function of the area blocked and the possibility of postoperative self-inflicted injury to soft tissues as a sequel to anesthesia.
Equipment
None of the regional nerve blocks for oral surgery in dogs and cats need any special equipment other than potentially 
hypodermic needles. The delivery site is premeasured to determine that the needle length will reach the site.
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