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Local anesthesia: intraoral

ISSN 2398-2950

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Introduction

  • General anesthesia General anesthesia: overview  and endotracheal intubation Endotracheal intubation with a cuffed endotracheal tube is required for any dental procedure. Sedation   Sedation or sedative protocol may be used for quick diagnostic procedures (ie radiographic examination).
  • Many patients in veterinary dentistry are older and/or have compromised core body functions. It is important to choose an anesthetic regimen that will provide these animals with the least risk and offer adequate analgesia Analgesia: overview intraoperatively and postoperatively. Regional anesthesia Local anesthesia: intravenous regional anesthesia (IVRA) is an excellent adjunct to general inhalation anesthesia because it will:
    • Allow the anesthetist to reduce systemic anesthesia levels (and risks) while providing appropriate intraoperative analgesia.   
    •  Aid in hemostasis and prolong analgesia when combined with specific drugs (eg dilute epinephrine 1:100,000). 
      Caution in hyperthyroidism or cardiac disease.
    • Provide long lasting postoperative analgesia when long acting solutions are used (ie bupivacaine Bupivacaine).
  • Despite some reports indicating that animals are more at risk for self-trauma to the locally anesthetized area during recovery from general anesthesia, this is not a typical response. Self-trauma occurs only when a block is made with excessive volume of drug or lack of attention to specific anatomical landmarks.

Body systems

  • The trigeminal nerve (CN5), and in particular its mandibular and maxillary branches, provides most of the innervation to the oral cavity in the dog and cat. The maxillary nerve at the rostral third of the pterygoid fossa gives off into the sphenopalantine nerve, later becoming the major palatine nerve. The maxillary nerve then enters the infraorbital canal and becomes the infraorbital nerve which provides innervation to the rostral teeth and gingiva, skin of the upper lips and nose. The mandibular nerve enters the mandibular  foramen on the medial aspect of the mandible and runs into the mandibular canal as inferior alveolar nerve, which innervates all mandibular teeth.

Dosage

  • Bupivacaine Bupivacaine:
    • Cats = 2 mg/kg (caution never exceed as a total dosage)  
    • Dogs = 2 mg/kg.
  • Syringe and 22 - 25 gauge x ¾ to 3 inch hypodermic needle.
  • Bupivacaine will take affect within 4-8 mins and will last 6-10 hours. The duration of anesthesia/analgesia may be increased, potentially doubled, with the addition of opioids such as morphine Morphine or buprenorphine Buprenorphine, as described in the brachial plexus block in humans. 

Technique

  • All regional nerve blocks as described below are performed intraorally as opposed to percutaneously. A 0.5% bupivacaine sterile solution is used at the following volume based on the patient size:
    • Small dog or cat = 0.1 ml/site.
    • Medium dog      = 0.2 ml/site.
    • Large dog          = 0.3 ml/site.
  • The needle is advanced slowly to the desired location. Aspiration is performed after rotating the needle 90° until a full 360° rotation has been accomplished. A small bleb of drug is infused and the aspiration is repeated to ensure that the needle is not in a vessel. The agent is then slowly injected. 
  • Four regional nerve blocks are commonly utilized to provide local analgesia to the different regions of the oral cavity. These blocks have confusing nomenclature in that the block may refer to the region blocked or the actual nerve that is blocked. This discussion suggests simplification and clarification of nomenclature to describe the region affected rather than the nerve blocked.  
  • Two blocks exist for the maxilla. The rostral maxillary block infiltrates the infraorbital nerve prior to exiting the infraorbital foramen. The caudal maxillary block anesthetizes both the maxillary nerve before it enters the maxillary foramen and the sphenopalatine nerve located ventral to the rostral third of the zygomatic arch.
  • The regional mandibular blocks include two blocks as well. The caudal mandibular infiltrates the mandibular nerve on the lingual aspect of the mandible prior to its entry into the mandibular canal (where it becomes the inferior alveolar nerve). The rostral mandibular anesthetizes the inferior alveolar nerve within the mandibular canal via the middle mental foramen. 
  • The regional nerve blocks for oral surgery are similar for the dog and the cat. The rostral maxillary block provides infiltration of the anesthetic solution adjacent to the infraorbital nerve. Within the infraorbital canal this nerve leaves the middle superior alveolar nerves to the fourth premolar tooth, and the incisivomaxillary nerve to first three premolar teeth, the canine and incisor teeth. In addition the rostral portion of the maxillary bone and surrounding soft tissue are affected. To perform this block, retract the lip dorsally. Palpate the infraorbital neurovascular bundle beneath the vestibular mucosa. This is a large cylindrical band that exits the infraorbital canal dorsal to the distal root of the maxillary third premolar. The thumb of one hand can be used to retract the bundle dorsally.  With the opposite hand the needle is advanced close to the maxillary bone ventral to the retracted bundle in a rostral to caudal direction to a point just inside the canal. The needle should pass without engaging bone. If bone is encountered the needle is withdrawn slightly and redirected until it passes resistance-free into the canal. However, several attempts should not be made with the same needle, as a damaged needle tip may lacerate the neurovascular bundle and surrounding tissues.
  • The caudal maxillary block allows infiltration of the local anesthetic combination adjacent to the maxillary nerve and the sphenopalatine nerve ventral to the caudal half of the zygomatic arch. These nerves supply sensory innervation to the maxilla. In addition to the structures affected by the rostral maxillary block, it will anesthetize the caudal cheek teeth and associated bone and soft tissue. The soft palatal mucosa and hard palatal mucosa and bone will also be affected. To perform this block the needle is introduced more caudally via the infraorbital canal. In cats and brachycephalic dogs, it is important to keep the syringe and needle parallel to the gingival margin to avoid injuring the eye. 
  • The rostral mandibular block infiltrates the rostral extent of the inferior alveolar nerve just before it exits the middle mental foramen. The structures anesthetized include the incisors, the canine and the first two premolars. The adjacent bone and soft tissue are also affected. The middle mental foramen is located about third of the distance from the ventral border to the dorsal border of the mandible at the level of the mesial root of the second premolar. The landmark for infiltration is the mandibular labial frenulum. The frenulum is retracted caudally. The needle is inserted at the rostral aspect of the frenulum and advanced along the mandibular bone (at ~ a 30° angle to the body of the mandible) to just enter the canal. If bone is encountered the needle should be backed out and redirected until the needle passes freely into the foramen. Placement can be confirmed by moving the syringe laterally to encounter the lateral aspect of the canal. The patients jaw, rather than the alveolar mucosa, will move slightly if the needle is within the canal. The needle will not likely be able to thread the canal as in the infraorbital block. 
  • The caudal mandibular block is performed by infiltrating the mandibular nerve prior to its entry into the mandibular foramen on the lingual aspect of the mandibular ramus by two methods. In the first method, an imaginary plumb line is drawn from the lateral canthus of the eye directly to the ventral mandible. The needle is inserted into the skin at the lingual aspect of the mandible at this point. The needle is advanced along the bone following the imaginary plumb line to a point 1/3 of the distance from the ventral to the dorsal mandiblular border. The needle will now be in the vicinity of the mandibular foramen where the mandibular nerve enters the mandibular canal. The second method is intraoral. The injection is made by passing the needle through the mucosa adjacent to the medial side of the ramus of the mandible. A finger is placed extraorally in a notch just rostral to the angle of the mandible and ventral to the condylar process. Here the mandibular nerve is located outside of the mandibular canal. This technique blocks all of the teeth of the mandible on the side of infiltration as well as the adjacent bone and soft tissue.

Medical, financial and environmental benefits

  • Regional nerve blocks are relatively easy to administer and require no special equipment to perform. Their use encourages quick return to normal mastication and continuation of normal food and water intake shortly after oral procedures. Incorporation of oral regional nerve blocks into the dentistry service is paramount in providing the best in patient care. 
  • The ability to obtain hours of postoperative pain management and the reduction of intraoperative general anesthesia has tremendous medical, financial and environmental benefits for the practice of veterinary dentistry. Clients appreciate the comfortable state of their pet at the discharge appointment.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Beckman B W, Legendre L (2002) Regional nerve blocks for oral surgery in companion animals. Comp Cont Ed Prac Vet 24 (6), 439-442 VetMedResource.
  • Candido K D, Winnie A P, Ghaleb A H et al (2002) Buprenorphine added to the local anesthetic for axillary brachial plexus block prolongs postoperative analgesia. Reg Anesth Pain Med 27 (2), 162-167 PubMed.
  • Bazin J E, Massoni C, Bruelle P et al (1997) The addition of opioids to local anaesthetics in brachial plexus block: the comparative effects of morphine, buprenorphine and sufentanil. Anaesthesia 52 (9), 858-862 PubMed.

Other sources of information

  • Rochette J (2001) Local Anesthetic Nerve Blocks and Oral Analgesia. In: Proceedings from the 26th World Congress of the World Small Animal Veterinary Association, August 2001, pp 250-252.
  • Haws I J (1999) Local Dental Anesthesia. In:  Proceedings from the Thirteenth Annual Veterinary Dental Forum, October 1999, pp 304-307.
  • Holmstrom S E, Frost P, Eisner E R (1998) Veterinary Dental techniques. Philadelphia, W.B. Saunders, pp 492-493.