Introduction

The prevalence of periodontal disease is reported to impact 30–80% of dogs and cats older than 3 years [1–4]. In addition, oral diseases are among the most common diagnoses made in small‐animal general practices [2]. Proper control and minimization of periodontal disease potentially reduces periodontal‐disease‐related bacteremia [5, 6] and systemic inflammatory factors (C‐reactive protein) [7], both of which may serve as risk factors for other systemic disorders. An association between periodontal disease and histologic changes in renal, hepatic, and the myocardial tissue has been proposed [8]. These changes could theoretically be linked to abnormal organ function, changes in anesthetic drug metabolism, and reduced drug effectiveness. In addition, the chronic pain and inflammation associated with periodontal disease can negatively impact an animal’s quality of life and their ability to heal.

Non‐anesthesia dental (NAD) procedures are dental techniques performed on conscious dogs and cats. Currently there is a lack of peer‐reviewed literature supporting that NAD procedures are safe or are as effective as anesthetized cleanings and oral examinations [9]. NAD procedures do not allow subgingival cleaning, periodontal probing, or radiographic evaluation. Performing dental procedures in this manner puts both the pet and operator at risk of being bitten or injured by sharp instruments. The American Veterinary Dental College [10], American College of Veterinary Anesthesia and Analgesia [11], and American Animal Hospital Association [12] all have positions or policy statements against NAD procedures. Without general anesthesia, a thorough and complete oral examination cannot be performed, and intraoral radiographs cannot be taken. Safe and judicious use of sedatives and anesthetics is necessary to facilitate appropriate assessment, diagnostics, and treatment of patients.

Fundamentally, periodontal disease itself will not directly affect sedative and anesthetic drug metabolism. However, chronic pain and inflammation associated with periodontal disease or other oral conditions may result in “wind‐up” pain. These patients may exhibit signs of central or peripheral nervous system sensitization and may require a higher analgesic dosing with multimodal analgesics owing to their heightened state of sensitivity. The severity or chronicity of oral disease may also impact the effectiveness of local anesthetic drugs due to the pathologic changes such as acidic pH of inflamed tissues altering uptake and action of these drugs.

Locoregional Anesthetic/Analgesic Agents

A variety of drugs are used in local and regional anesthesia for procedures involving the oral cavity. Appropriately placed regional anesthetic blocks in the oral cavity have been shown to reduce the amount of inhalant anesthetic by as much as 23% [13]. Of the sodium channel blockers used in local and regional anesthesia, the amide family of drugs, which includes lidocaine and bupivacaine, is the most common. Toxic or maximum doses should always be considered when deciding how much local anesthetic to administer [14].

There has been a trend in the anesthesia and pain management of human patients to combine drugs with differing mechanisms of action to enhance or prolong the anesthetic or analgesic potential of local or regional blocks. The addition of opioids and alpha‐2‐adrenergic receptor agonists with a local anesthetic appears to demonstrate the best potential for enhancing pain relief. For example, chronic nociceptive stimulation results in the upregulation of mu‐opioid receptors in the peripheral nervous system [15]. In human patients, mixing an opioid with the local anesthetic extends the duration of postoperative analgesia [16, 17]. Although not statistically significant, one study in dogs suggests that buprenorphine mixed with local anesthetic in regional dental blocks may extend the block duration over bupivacaine alone [18]. Clinically, buprenorphine mixed with the local anesthetic and administered in local and regional blocks may be used. The use of alpha‐2‐adrenergic receptor agonists, such as dexmedetomidine, combined with local anesthetics or administered as a local anesthetic may also benefit patients [19]. When alpha‐2‐adrenergic receptor agonists are used as a local anesthetic in humans, pain management occurs at the local level without evidence of hemodynamic side effects from systemic absorption [20]. More chronic conditions may have the additional recruitment of peripheral mu receptors [21] and, therefore, benefit the most from synergy between the locally administered opioid, alpha‐2‐adrenergic receptor agonists, and local anesthetics. The combination of epinephrine and a local anesthetic is commercially available and may improve the local anesthetic duration due to vasoconstrictive effects slowing tissue clearance of the local anesthetic, as well as epinephrine demonstrating primary antinociceptive activity [19].

While a longer local anesthetic duration may be desirable in many situations to encourage a smooth recovery and extend surgical site anesthesia, the presence of intraoral sutures and lack of sensation at a maxillary surgery site may result in complications with healing. In maxillary procedures, such as resections or oronasal fistula repair, excessive tongue pressure against the surgery site may be disadvantageous and the use of longer‐acting local anesthetics may be undesirable. In theory, since the surgical site is blocked by local anesthetics, and the tongue that maintains sensation can feel the sutures, the animal may be preoccupied with the abnormal feeling of foreign material in the oral cavity. The tongue may continue to rub and/or put pressure on the surgical site longer when long‐acting local anesthetics are used, potentially increasing the risk of surgical closure dehiscence to a greater degree than with short‐acting local anesthetics. In particular, in major oral surgery cases with associated chronic discomfort, the addition of buprenorphine to a short‐acting local anesthetic may improve analgesia through the interaction with peripheral mu receptors while not prolonging local anesthesia [15]. In major oral surgery where postoperative pain management with regional anesthesia is desirable, surgical disruption of the normal anatomy may be so extensive that reliable and predictable delivery of regional anesthetic nerve blocks is not possible. A recently available formulation of bupivacaine liposome injectable suspension is available and designed to provide postoperative pain relief for 72 h when infiltrated into surgical site tissues [22]. Further data are needed to determine whether this drug delivers safe and effective pain management when delivered as a peripheral nerve block for dental procedures [23].

Locoregional Agent Administration

Regional and local anesthetic use in humans is widely accepted as beneficial. Complications associated with inferior alveolar nerve blocks, including prolonged paresthesia or paralysis, have been reported to occur in 0.00013–0.01% of human dental patients [24]. Local and regional anesthesia in humans permits procedures including extraction and root canal therapy to be performed on an outpatient basis. One potential complication that generates much anxiety among veterinarians is inadvertent anesthesia of the tongue and subsequent patient responses to the anesthetized tongue during recovery. However, peripheral nerve paresthesia and subsequent self‐mutilation involving the tongue of both veterinary and human patients are only anecdotally reported.

Injection and placement of local anesthetic may cause physiologic responses, even in the anesthetized patient, because many commercial products have an acidic pH. If an increase in heart rate, respiratory rate, or physical reaction is present, this may be loosely interpreted as confirmation that the local anesthetic has been administered in the correct location. However, the absence of a reaction does not correlate to the local anesthetic being placed in the incorrect location, as the patient may be in a deep anesthetic plane that renders them unresponsive.

When considering needle placement and injection, some resources recommend needle bevel placement in a particular orientation when performing nerve blocks with local anesthetics. With accurate placement approximated to the target nerve, bevel direction may be less important. Placing the local anesthetic in areas over the periosteum adjacent to the foramen out of which the nerve emerges will help to distribute the anesthetic once the needle is removed and digital pressure is applied. A variety of different needle types have been used in human patients with varying results. Standard short bevel needles used in veterinary patients are sufficient for placing regional dental and oral surgical blocks. Once the needle penetrates mucosa, it should be advanced slowly to minimize the risk of nerve or vessel penetration. However, unless the vessel or nerve is confined, the neurovascular structures should be displaced by the bevel rather than penetrated [25]. Some resources advocate the use of very‐small‐gauge needles. Although the physical tissue injury would be much smaller, human anesthesiologists exerted more digital plunger pressure during local anesthetic injection than they realized, translating to faster velocity and greater tissue injury with a smaller‐gauge needle [25]. With the small volumes used in the administration of veterinary dental blocks, 25‐ to 27‐gauge, 1–1¹/₂‐in. needles are commonly used in canine and feline patients undergoing oral surgery to minimize this trauma.

A wide variety of local anesthetic dosage volumes for dental patients have been reported in the literature without substantial evaluation of these volumes versus clinical effectiveness or duration of action. Dye perfusion studies have reported use of volumes in cadavers ranging from 0.4 ml (inferior alveolar block) to volumes of 1–3 ml [26] for a maxillary block using the modified infraorbital approach (through the infraorbital canal described in the following text) [27]. Delivering small volumes with accurate placement to achieve clinical effect may minimize the risk for accidental anesthesia of unintended structures such as the tongue.

When performing local or regional anesthetic blocks, aspirating (“drawing back”) negative pressure to avoid intravascular delivery is essential. Because of the beveled orientation of the needle tip, spinning the syringe barrel 90° along the long access and reaspirating should, at some point, draw the bevel off the vessel wall and result in blood drawn into the syringe if it is intravascular. If blood is drawn into the syringe, advance the needle slightly forward or backward and reaspirate. If repeated attempts result in aspiration of blood, remove the needle and try positioning it again. Medication should be administered with the needle placed on the periosteum for the middle mental and caudal mandibular blocks. Even if the bevel is not directly over the nerve, by injecting on the periosteum, the local anesthetic will cover more surface area and increase the chance that the nerve will be contacted. Once the local anesthetic has been administered, the needle should be withdrawn and digital pressure applied for 1 min to provide adequate time for prevention of hematoma formation. Injection should not be continued as the needle is withdrawn because inadvertent intravascular injection may result if the vessel was perforated during needle placement.

Commonly reported local anesthetics used for nerve blocks include lidocaine, bupivacaine, lidocaine/bupivacaine combinations, ropivacaine, mepivacaine, and combinations including epinephrine. Bupivacaine and lidocaine appear to be the most frequently reported local anesthetics used in dentistry and oral surgery patients with ropivacaine being a commonly used substitute for bupivacaine. Some variability exists regarding the reported time to onset and duration of activity of these medications; however, general expectations regarding onset of action and duration of action are illustrated in Table 13.1. Because the total maximum dose varies between bupivacaine and lidocaine, careful calculations must be made before mixing these medications. Mixing lidocaine with bupivacaine for infraorbital blocks in dogs showed an increased duration of activity as compared to lidocaine alone [29]. However, onset times were not specifically evaluated and the duration of action of bupivacaine only was not reported. Some pharmacists caution the mixing of lidocaine with bupivacaine fearing that the solution pH and pKa will render the bupivacaine partially unavailable. Any potential shorter duration of onset for anesthesia with lidocaine should be carefully weighed against decreased duration of effectiveness of bupivacaine if this mixture is going to be used.

Bupivacaine or ropivacaine are commonly used in local and regional anesthesia for patients undergoing oral surgery because they have a longer duration of activity than lidocaine [28, 30]. The use of bupivacaine provides ample time to deliver oral systemic pain medications before the local anesthetic wears off. Bupivacaine’s 6–10 min onset of action is considered intermediate. The duration of action may reach 4–6 h when placed in areas predominately involving soft tissue or 6–8 h when placed in a foramen [30]. Whichever drug is chosen, careful attention should be made to the drug concentration listed on the bottle, as bupivacaine is available in many concentrations including 0.25%, 0.5%, and 0.75% solutions.

Maxillofacial Locoregional Techniques

When performing the middle mental or major palatine nerve blocks, the needle should not be threaded into the foramen. Placing the needle into the foramina risks transecting or lacerating the nerve. Krug and Losey (2011) reported that the actual penetration of the local anesthetic medication into the middle mental foramen was questioned, as well as its clinical effectiveness [31]. Thus, innervation to the teeth, oral cavity soft and hard tissues, and soft tissues of the face may be an intricate assortment of contributions from branches of multiple cranial nerves [31]. Because few measures of clinical areas of desensitization exist in veterinary patients, regional anesthetic blocks should be administered as a component of multimodal pain management, not a sole source of anesthesia and pain management.

In cases where surgical manipulation will approach midline, as in extracting the first or second incisors or biopsy near the palatal midline, consideration should be given to the potential for crossover innervation to occur [32, 33]. Likewise, one should also consider the surgical manipulation associated not only with extraction, but also with closure. In addition, patients may not be adequately anesthetized by an infraorbital regional block when palatal tissues are undermined during extraction of canine or premolar teeth. In most situations, the caudal maxillary block or inferior alveolar blocks may provide more complete regional anesthesia (Table 13.2).

Intraosseous and intraligamentary anesthesia techniques have been described (Table 13.2) [34, 35]. Veterinary patients commonly require multiple intraoral procedures to be performed. Rather than multiple intraligamentary or intraosseous anesthetic blocks for adequate regional anesthesia, a single regional anesthetic injection may anesthetize an entire quadrant of the mouth. Local anesthetic administration using intraligamentary or intraosseous techniques may successfully anesthetize focal areas of the mouth, but may require the use of specialized needles and injection ports [34]. These blocks are performed by placing the needle into the intraligamentary space in several areas around the affected tooth. This technique targets the sensory fibers of the tooth’s pulp. Very small volumes of local anesthetic are used in both intraosseous and intraligamentary local anesthesia.

Specific Regional and Local Blocks

Intraligamentary and Intraosseous Blocks

Intraligamentary and intraosseous local anesthetic blocks provide the most focal form of local anesthesia. These techniques are not performed as commonly in veterinary medicine because they often require the use of special syringes, needles, and dosing cartridges. However, veterinary dental patients often have multiple locations within the oral cavity and within the same quadrant where a single regional block will provide anesthesia. The effectiveness of a local block of a specific tooth may be difficult to assess in veterinary patients; these techniques may be more appropriate to address pulpal innervation, an assessment not commonly performed in general practice. As opposed to regional anesthetic blocks, local anesthetic techniques may be less effective at providing anesthesia when soft tissue flaps are created, and osteotomies are performed to facilitate tooth removal. The periodontal ligament space and root anatomy may also offer challenges, as the density of alveolar bone is greater in veterinary patients than it is in humans [35].

Intraligamentary injections are performed by injecting 0.2 ml of local anesthetic per root at various locations around the root surface into the periodontal ligament space (Figure 13.1). A special dosing syringe is necessary, and, in cases of severe periodontal disease, the pH of the inflamed environment may decrease the lipophilicity and efficacy of the anesthetic. Intraosseous anesthetic delivery requires an intraosseous delivery needle, which is inserted into the interproximal bone for anesthetic delivery. A unique injection port remains in place for additional anesthetic delivery [35].

Infraorbital Block

The infraorbital block is performed by administering the local anesthetic within the infraorbital canal. Signal transmission is blocked at the level of the infraorbital nerve. Ramifications in the floor of the infraorbital canal course through the alveolar bone and are responsible for innervating the ipsilateral maxillary incisors, canine tooth, first, second, and third premolar teeth, buccal mucosa, portions of the ipsilateral lip, and soft tissues of the rostral cheek (Figure 13.2). Local anesthetic placement in this location may not reliably anesthetize the palatal mucosa and fourth premolar tooth, and may not completely anesthetize the central incisors because of crossover innervation. Small volume delivery with accurate placement may be best to achieve clinical effect with dosing varying from 0.1 mL in small dogs and cats up to 0.5 ml in large‐breed dogs.

The upper lip should be reflected dorsally and the neurovascular bundle digitally palpated. The infraorbital canal and neurovascular bundle should be palpable at the level of the maxillary third premolar distal root. After palpating these structures, the needle can be inserted through the mucosa and directed along the neurovascular bundle and into the canal (Figures 13.3 and 13.4). To reduce traumatizing the globe, maintain the syringe parallel to the hard palate. Once the needle is advanced through soft tissues to the infraorbital canal opening, it is important to aspirate with the syringe in order to ensure the needle bevel is not intravascular. Digital pressure should be applied for 1 min after withdrawal of the needle to prevent leakage of the local anesthetic and reduce the likelihood for hematoma development as a result of inadvertent vessel puncture.

Caudal Maxillary Block

Proper placement of the caudal maxillary nerve block will anesthetize the maxillary teeth in the ipsilateral quadrant, lip, hard/soft palatal mucosa, and buccal soft tissues. While ultrasound‐guided techniques provide accurate and precise local anesthetic placement at the level of the trigeminal nerve for major caudal maxillectomy procedures, conventional anatomic landmark‐based delivery of local anesthetics commonly occurs in practice [36]. By guiding the needle through the infraorbital canal and into the suborbital soft tissues, the needle tip should approximate the course of the maxillary branch of the facial nerve at the level of the sphenopalatine nerve (Figure 13.5). The local anesthetic should be administered when the needle tip has been advanced to a point immediately caudal to the last molar tooth (Figure 13.6). Successful block in large‐breed dogs may require the use of a 3‐in. spinal needle, although 1½‐in. needle length typically provides adequate clinical effect (Figure 13.7

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