Regional nerve blocks key to delivering quality dental care
Sep 01, 2007
This article details techniques that can be incorporated into companion-animal-hospital dentistry service to maximize safety, care and comfort for patients undergoing oral surgical procedures.
This discussion suggests adopting less misleading names for the regional nerve blocks, relying on simple anatomical regions blocked rather than traditional confusing nomenclature.Detailed descriptions of regional and local nerve blocks commonly used to provide analgesia for oral surgery in veterinary patients have appeared in numerous publications.
Complete analgesia to the targeted tissue and a reduction in the concentration of the inhalant anesthetic are two significant benefits of proper administration of local agents. Hypotension, bradycardia and hypoventilation are complications that can be minimized by the use of local and regional blocks for oral surgery. Local blocks eliminate the perception of pain, making surgical anesthetic depths unnecessary.
This author commonly uses lidocaine and bupivicaine combined in the same syringe for regional oral-nerve blocks. Lidocaine is not desirable as a sole agent due to its limited effect post administration (one to two hours). Bupivicaine requires administration much earlier in the anesthetic event than lidocaine in order to be effective prior to surgical tissue manipulation. These limitations can be minimized or eliminated by using them in combination. The quick onset of lidocaine, coupled with bupivicaine's extended duration of effect (up to eight hours), make them a good choice for combined use in regional nerve blocks. The agents may be used with or without epinephrine.
Although rare, complications are possible with inadvertent systemic administration or systemic uptake of locally delivered local-anesthetic agents. Central nervous system excitement, including seizures, followed by depression, apnea, severe cardiovascular compromise, dysrhythmias and hypotension are all possible. Direct toxicity to skeletal muscle and anaphylactic reactions are possible with local administration. The author has never experienced any of these complications at the doses recommended in this article.
The author currently uses opiates in the lidocaine/bupivicaine mixture for procedures where increased duration of effect are desirable. Patients that are particularly difficult to medicate, either in the hospital or at home, may benefit from this combination.
Chronic pain states, as seen in canine or feline stomatitis, may make post-operative pain management challenging. Morphine may be used as a portion of the premedication protocol at 0.5 mg/kg IM 20 minutes prior to induction. One-fourth of that same volume is added to the local mixture per site to be blocked. Hydromorphone is administered at 0.1 mg/kg as a portion of the premedication protocol. One-fourth of that same volume is added to the local mixture per site to be blocked. Buprenorphine may be used as a premedication at 0.015 mg/kg following the same volume recommendations for local infiltration as with the examples above.
Morphine and hydromorphone are pure mu agonists and are preferred for management of severe pain. Buprenorphine, a partial mu agonist, is a good choice for mild to moderate pain. All three agents may be used in either species, but pure mu agonists, in particular hydromorphone, are known to cause hyperthermia in cats. If pure mu agonists are used either locally or systemically in cats, temperature should be monitored during and up to five hours post procedure.
None of the regional nerve blocks for oral surgery in dogs and cats need any special equipment to employ. A tuberculin syringe with a 5/8-in., 25-gauge needle is used for patients 4 kg or less. Three-or 6-ml syringes with 22-25 gauge, 3/4-in. needles are used for patients more than 4 kg, depending upon the volume to be infused. The correct dose of the desired agents is drawn. The needle is advanced to the desired location. Aspiration is performed to ensure the needle is not in a vessel and the agent is dispersed. If one encounters a vessel, the needle is redirected and aspiration repeated. Once extravascular placement is confirmed, the agent is administered. Be careful not to advance the needle during injection to avoid inadvertent vessel penetration.