Regional Nerve Blocks Key to Delivering Quality Dental Care
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2S SMALL ANIMAL DVM NEWSMAGAZINE september 2007 DENTISTRYDENTISTRY By Brett Beckman DVM, Dipl. ACVD, Dipl. AAPM Brett Beckman, DVM, FAVD, Dipl. AVDC practices referral dentistry at Affiliated Veterinary Specialists, Or- lando, Fla.; Noah's Animal Hospitals in Indianapolis; and at Florida Veteri- Photo 1: Mesial and distal are locational terms used to describe proximity to a certain tooth. nary Dentistry and Oral Surgery in In this example the arrows are pointing to regions both mesial and distal to the mandibular Punta Gorda, Fla. He is president-elect left third premolar. of the American Veterinary Dental So- ciety and diplomate of the American Academy of Pain Management. Second in a series Regional Photo 2: Rostral maxillary (infraorbital) block. Retraction of the infraorbital neurovas- cular bundle in a dorsal direction allows for the needle to pass ventral to the bundle to enter Photo 3: Proper needle placement for the nerve blocks key the infraorbital foramen. rostral maxillary block on a skull. to delivering quality dental care he use of regional nerve tration of the inhalant anesthetic are blocks for oral surgery in dogs two significant benefits of proper ad- and cats is synonymous with ministration of local agents. Hypoten- Photo 5: Cadaver specimen demonstrating quality patient care. sion, bradycardia and hypoventilation Photo 4: Caudal maxillary (maxillary) needle placement for the caudal maxillary This article details tech- are complications that can be mini- block. The mouth is opened wide and the nee- block. The needle is adjacent to the infraor- niques that can be incor- mized by the use of local and regional dle passed into the mucosa caudal to the max- bital nerve and the pterygopalatine nerve and Tporated into companion-animal-hos- blocks for oral surgery. Local blocks illary second molar. its ventral branches. pital dentistry service to maximize eliminate the perception of pain, mak- safety, care and comfort for patients ing surgical anesthetic depths unnec- undergoing oral surgical procedures. essary. This discussion suggests adopting less misleading names for the regional Agents nerve blocks, relying on simple anatom- This author commonly uses lido- ical regions blocked rather than tradi- caine and bupivicaine combined in the tional confusing nomenclature. same syringe for regional oral-nerve Detailed descriptions of regional blocks. Lidocaine is not desirable as a and local nerve blocks commonly used sole agent due to its limited effect post to provide analgesia for oral surgery administration (one to two hours). Photo 6: Rostral mandibular (mental) block. in veterinary patients have appeared Bupivicaine requires administration The mandibular labial frenulum is retracted in numerous publications. much earlier in the anesthetic event in a ventral direction. The needle is passed Complete analgesia to the targeted than lidocaine in order to be effective into the rostral aspect of the frenulum adja- Photo 7: Proper needle placement for the tissue and a reduction in the concen- Continued on page 4S ᮣ cent to the bone and into the foramen. rostral mandibular block on a skull. 4S SMALL ANIMAL DVM NEWSMAGAZINE september 2007 REGIONAL NERVE BLOCKS Opiates Based on human research, the use Continued from page 2S of local analgesics and opiates in com- prior to surgical tissue manipulation. bination provides extended duration of These limitations can be minimized or action. The addition of morphine or eliminated by using them in combina- buprenorphine to a regional brachial tion. The quick onset of lidocaine, cou- plexus block for limb amputation pled with bupivicaine’s extended du- demonstrated close to a twofold increase ration of effect (up to eight hours), in duration of effect over patients re- make them a good choice for com- ceiving only bupivicaine in one study. bined use in regional nerve blocks. The A similar model was used in another agents may be used with or without study where researchers demonstrated epinephrine. that the addition of buprenorphine to Although rare, complications are the regional block provided significant possible with inadvertent systemic ad- increases in duration compared to giv- ministration or systemic uptake of ing the buprenorphine intramuscularly. Figure 8: Caudal mandibular (inferior alve- locally delivered local-anesthetic agents. The author currently uses opiates olar) block. A plumb line is drawn from the lat- Central nervous system excitement, in- in the lidocaine/bupivicaine mixture eral canthus to the ventral border of the cluding seizures, followed by depres- for procedures where increased dura- mandible. The needle is placed through the sion, apnea, severe cardiovascular com- tion of effect are desirable. Patients that skin adjacent to the lingual aspect of the promise, dysrhythmias and hypoten- are particularly difficult to medicate, mandibular bone. It is advanced to a point sion are all possible. Direct toxicity to either in the hospital or at home, may one-third of the distance from the ventral to Photo 9A: Proper needle placement for the skeletal muscle and anaphylactic reac- benefit from this combination. dorsal border of the mandible. caudal mandibular block on a skull. tions are possible with local adminis- Chronic pain states, as seen in ca- tration. The author has never experi- nine or feline stomatitis, may make enced any of these complications at the post-operative pain management chal- doses recommended in this article. lenging. Morphine may be used as a portion of the premedication proto- Dosing considerations col at 0.5 mg/kg IM 20 minutes prior A maximum dose of 1.0 mg/kg of to induction. One-fourth of that same each agent in combination in the same volume is added to the local mixture syringe is recommended. Care should per site to be blocked. Hydromorphone be exercised, especially in smaller pa- is administered at 0.1 mg/kg as a por- tients and cats, so that maximum doses tion of the premedication protocol. are not exceeded. The ratio of lidocaine: One-fourth of that same volume is bupivicaine is 1:4 when using concen- added to the local mixture per site to trations of 2 percent and 0.5 percent, be blocked. Buprenorphine may be respectively. The total volume used de- used as a premedication at 0.015 mg/kg pends on the size of the patient and the following the same volume recommen- Photo 10: Radiopaque dye infused local Photo 9B: This view is from the lingual as- number of sites that require analgesia. dations for local infiltration as with anesthetic mixture placed at the level of the pect of the mandible to demonstrate the mandibular canal for the caudal mandibu- The maximum number of sites would the examples above. mandibular foramen for the caudal mandibu- lar block to demonstrate the extensive diffu- be four if the patient requires surgical Morphine and hydromorphone are lar block. sion along the mucosa/bone interface. manipulation in all four quadrants. pure mu agonists and are preferred for Table 1 (p. 5S) shows recommended management of severe pain. Buprenor- infusion volumes per site based on pa- phine, a partial mu agonist, is a good tient size. Please note that these vol- choice for mild to moderate pain. All umes represent both agents mixed to- three agents may be used in either gether. Table 2 (p. 7S) shows a sample species, but pure mu agonists, in par- calculation for a 4-kg dog. ticular hydromorphone, are known to Physiologic parameters will deter- cause hyperthermia in cats. If pure mu mine if the block is effective. If blood agonists are used either locally or sys- pressure, heart rate and respiration rate temically in cats, temperature should increase with surgical manipulation, be monitored during and up to five the block either was not correctly placed hours post procedure. or hasn’t had the proper amount of time for onset (five minutes). If enough Equipment time has elapsed and the attending vet- None of the regional nerve blocks erinarian believes the time for onset is for oral surgery in dogs and cats need not an issue, then the block may be re- any special equipment to employ. A peated as long as the maximum total tuberculin syringe with a 5/8-in., 25- Figure 12: The arrow demonstrates the lo- dose is not exceeded. It should be noted gauge needle is used for patients 4 kg Photo 11: The arrow shows the infraorbital cation of the middle mental foramen, the land- that the low ph of inflamed tissue will or less. Three- or 6-ml syringes with foramen in the cat. Please note that it is only mark for needle introduction in the rostral render local anesthetics less effective. 22-25 gauge, ?-in. needles are used for a few millimeters in length. mandibular block in the cat. 5S september 2007 www.dvmnews.com SMALL ANIMAL TABLE 1 monly used to provide local analgesia Two blocks exist for the maxilla. The lar infiltrates the inferior alveolar nerve Recommended infusion volumes to the different regions of the oral cav- rostral maxillary infiltrates the infra- on the lingual aspect of the mandible ity. These blocks have confusing nomen- orbital nerve prior to exiting the in- prior to its entry into the mandibular Feline/small dog up to 6 kg = 0.1-0.3 ml clature in that the block may refer to fraorbital canal. The caudal maxillary canal. The rostral mandibular anes- the region blocked or the actual nerve anesthetizes both the infraorbital nerve thetizes the inferior alveolar nerve Medium dog 6-25 kg = 0.3-0.6 ml that is blocked. This discussion sug- and pterygopalatine nerve caudal to within the mandibular canal via the Large dog 26-40 kg = 0.8 -1.2 ml gests simplification and clarification of the second maxillary molar. The re- mental foramen. Extra-large dog, over 41 kg = 1.4 -1.6 ml nomenclature to describe the region gional mandibular blocks include two affected rather than the nerve blocked.