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Veterinarian Technician May 2009 (Vol 30, No 5)

Dental Checkup — The Benefits of Regional Dental Blocks

by Benita Cherry

    Technicians can play a pivotal role in pain prevention by learning the technical skills necessary to assist in performing regional and local nerve blocks. The need for regional nerve blocks and local infiltration analgesia — even for anesthesia in general — in pets was not recognized until the past 10 to 15 years.1 Regardless, clients today identify with the pain associated with dental procedures and, therefore, appreciate the need for their pet to have regional or local anesthesia during a dental procedure to ensure, as much as possible, a comfortable, pain-free recovery.2

    Why Use Regional or Local Infiltration Anesthesia?

    The use of regional anesthetics has many advantages for veterinary dental patients, including:

    • Providing extensive analgesia to the targeted tissues, thereby reducing the quantity of inhalant anesthetic required and eliminating any roller coaster effect if the anesthetized patient perceives painful stimuli.2
    • Reducing the amount of inhaled anesthetic needed to lower the incidence of adverse events caused by low blood pressure from vasodilation and bradycardia from excessive anesthetic depth.5
    • Reducing convalescence time and promoting overall patient recovery.3

    Some veterinary dentists find that when a good block is in place for a painful procedure, such as an extraction, lower levels of inhalant anesthetic are required, which can quicken the recovery time (length of anesthesia can affect recovery time as well as depth of anesthesia required). Quicker recovery has beneficial effects, especially on the patient's blood pressure (Personal communication, Patricia Frost-Fitch, DVM, DAVDC, La Center, Wash., January 2009). In addition, some dentists find that the infraorbital block in particular is generally easy to perform on most patients and can help provide analgesia to the caudal maxilla as well as the rostral maxillary teeth.

    Drugs used in regional anesthesia, such as bupivacaine hydrochloride 0.5%, mepivacaine 2%, and lidocaine hydrochloride 2%, affect all three areas of the nociceptive pathway: transduction, transmission, and modulation.5 Because of its duration of action (3 to 10 hours), bupivacaine hydrochloride 0.5% with or without epinephrine is the regional dental anesthetic used most often in veterinary dentistry.2 (See the section on Regional Anesthetic Drugs and Doses for a comparison of the duration of action for bupivacaine, mepivacaine, and lidocaine.)

    Naturally, risks are associated with the use of regional anesthetics, and some veterinary dentists have found that nerves, bone, or blood vessels have been damaged from aggressive or inappropriate attempts to perform nerve blocks. Unlike humans, pets cannot alert caregivers about persistent numbness or tingling (Personal communication, Patricia Frost-Fitch, DVM, DAVDC, La Center, Wash., January 2009).

    In addition, there have been reports of accidental intravenous injection, which can cause cardiotoxicity or arrhythmias when bupivacaine 0.5% is used, and excessive doses of lidocaine hydrochloride 2% administered intravenously have reportedly caused CNS or cardiac toxicity.6 Furthermore, because feline patients have a much lower threshold for drug toxicities than canine patients do, lidocaine hydrochloride should be used cautiously in cats.

    Although quite rare, cases of self-trauma have been documented from the lack of sensation to the patient's tongue during recovery from regional anesthesia. Tongue chewing can be prevented by placing the patient in sternal recumbency and monitoring the patient closely.5

    Role of the Veterinary Technician

    Veterinary technicians play a major role as advocates of pain prevention and control. Often they are involved in the initial oral examination of an awake, cooperative patient and are, therefore, aware of existing problems, such as severe periodontal disease, tooth mobility, furcation exposure, fractured tooth crowns or roots, missing teeth, oral masses, oronasal fistulas, or other treatable issues. Therefore, technicians can provide key information needed by the veterinarian to devise a treatment strategy. For example, chronic oral pain associated with a long-standing fractured tooth or persistent oral soft tissue process, such as severe periodontal disease, oral cancer, or stomatitis, requires a comprehensive and intensive plan to lower the pain stimulus, thereby facilitating relief from pain wind-up.5

    Under the supervision of the veterinarian, technicians can stabilize the patient and expedite the administration of appropriate regional anesthetics, which allows adequate time for the onset of drug action before any noxious stimulation is introduced. Thorough knowledge of cranial anatomy and foramina is, therefore, required. The technical execution of regional nerve block techniques used in veterinary dentistry is summarized in Figures 1 ,2, 3 and 4 .

    Regional Anesthetic Drugs and Doses

    The maximum toxic dose should be recalculated each time a dental procedure is performed on a patient. This step is crucial in controlling risk factors associated with anesthesia. In addition, before each regional block, a predetermined quantity of drug not to exceed the total maximum volume of anesthetic should be established.

    Bupivacaine 0.5% has a delayed onset of action of at least 6 to 10 minutes, with some reports of up to 30 minutes after the agent has been injected into a foramen. However, as previously mentioned, its duration of action is 3 to 10 hours.6 If bupivacaine is used during an infiltration technique, it will remain effective for 4 to 6 hours.5 The maximum total dose of bupivacaine 0.5% is 2 mg/kg in canine and feline patients.6,7

    Because the onset of action for mepivacaine 2% also is lengthy at 7 to 15 minutes and the duration of action is only 2 to 2½ hours, this agent is not used often for dental procedures. However, it may cause less irritation to tissues than can occur with lidocaine.8 The dose for local infiltration is variable; for epidurals, the recommended dose is 0.5 ml q30sec until reflexes are absent.8

    Lidocaine hydrochloride 2% has a quick onset of action — 3 to 5 minutes — but is removed from the bloodstream rapidly and becomes ineffective after 1 to 1½ hours. Because it is metabolized by the liver, lidocaine should be used cautiously in patients with liver disease.2,5

    The addition of epinephrine to lidocaine or bupivacaine can cause vasoconstriction but increases the duration of action for both anesthetic agents.2 Currently, however, no veterinary formulations contain epinephrine, although some human formulations do.8

    Products containing epinephrine should not be used in patients with hyperthyroidism or cardiac disease or with the use of halothane as an inhalant anesthetic.2 A combination of lidocaine and bupivacaine in a 50-50 mixture diluted with sterile saline also has been used to appreciate the benefits of both drugs — the quick onset of lidocaine and the longer duration of action of bupivacaine.6

    Great care must be taken not to exceed the maximum dose for either lidocaine or bupivacaine, and a reduction in the total amount by 50% is advised to prevent accidental overdose, as the toxic dose of the two drugs used in combination can be additive.6

    When using a 50-50 mixture of lidocaine and bupivacaine without epinephrine, the recommended dose is 0.1 to 0.2 ml per site for a 10-lb dog or a cat, using the lower amount if all four quadrants are to be blocked. Mid-size canine patients can receive 0.25 to 0.3 ml per site, whereas large-breed dogs can receive 0.5 ml (Personal communication, Patricia Frost-Fitch, DVM, DAVDC, La Center, Wash., January 2009).

    Closing Remarks

    With the use of dental models (i.e., skulls), photographs, dental radiographs, and other visual aids, the technician can explain to clients how regional dental anesthetics are used and how they prevent pain.

    After the preanesthetic and regional nerve block agents have dissipated, technicians need to emphasize the need for postoperative pain relief measures. In most instances, regional anesthetics wear off completely after 6 to 10 hours.

    1. Carmichael D. Using intraoral regional anesthetic nerve blocks. Vet Med 2004;Sept.:766-770.

    2. Bellows J. Small Animal Dental Equipment, Materials and Techniques: A Primer. Ames, Iowa: Blackwell; 2004:105-113.

    3. Tranquilli WJ, Grimm KA, Lamont LA. Pain Management for the Small Animal Practitioner. Jackson, Wyo.; Teton New Media; 2000.

    4. McLain Madsen L. Perioperative pain management. Veterinary Technician 2005;26(5):359-368.

    5. Beckman BW. Pathophysiology and management of surgical and chronic oral pain in dogs and cats. J Vet Dent 2006;23(1):50-59.

    6. Holmstrom SE, Frost P, Eisner ER. Veterinary Dental Techniques for the Small Animal Practitioner, ed 2. Philadelphia: WB Saunders; 2004:626-636.

    7. Beckman BW, Legendre L. Regional nerve blocks for oral surgery in companion animals. Compend Contin Educ Pract Vet 2002;24(6): 439-444.

    8. Tilley LP, Smith FWK Jr. Blackwell's Five Minute Veterinary Consult: Canine & Feline, ed 4. Oxford, U.K.: Blackwell Publishing; 2007:1473,1500,1504.

    References »

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