Regional Anesthesia of the Head and Neck

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Chapter 30

Regional Anesthesia of the Head and Neck

James T. Amsterdam and Kevin P. Kilgore

Review Box 30-1 Regional anesthesia of the head and neck: indications, contraindications, complications, and equipment.

Intraoral and extraoral regional anesthesia is simple and convenient for everyday use in the emergency department (ED).¹ Nerve blocks provide anesthesia to broad areas of distribution on the face with a minimal amount of anesthetic and tissue distortion. Local anesthetic blocks are effective for closing facial lacerations, especially those of the lips, forehead, midface, and ears, places where the swelling caused by local infiltration may be undesirable. Local anesthetic blocks are also effective for the relief of pain, for anesthesia during facial débridement, and for diagnostic purposes.

Regional blocks are also therapeutic for procedural anesthesia and for control of pain in dental emergencies such as toothaches and dry sockets (see Chapter 64). Patients with dental pain who do not obtain relief with a regional dental block most likely do not have pain of dental origin. In cases in which the patient is thought to be seeking drugs, a dental anesthetic block is frequently the treatment of choice as an alternative to narcotics.

Topical anesthetic solutions such as tetracaine-adrenaline-cocaine (TAC) solution are useful for small lacerations of the scalp and face because of the vascularity of these areas. TAC is not to be used on or near the mucous membranes or the eye (see Chapter 29). More extensive discussion of the general complications of local anesthetics and regional anesthesia is provided in Chapters 29 and 32, respectively. Ophthalmologic anesthesia is discussed in Chapter 62, and blocks about the ears and nasal anesthesia are discussed in Chapter 63.

The procedures and techniques described here generally carry low morbidity. The supraperiosteal, mental nerve, and more sophisticated blocks (e.g., inferior alveolar block) are best learned under the instruction of an experienced clinician, a dentist, or an oral and maxillofacial surgeon.

Anatomy of the Fifth Cranial (Trigeminal) Nerve

The fifth cranial nerve, known as the trigeminal nerve, is the sensory nerve to the face (Fig. 30-1A) and the largest of the cranial nerves. It takes its origin from the midbrain and enlarges into the gasserian, or semilunar, ganglion. Each gasserian ganglion supplies one side of the face. The gasserian ganglion is a flat, crescent-shaped structure approximately 10 mm long and 20 mm wide that divides into three branches: the ophthalmic, maxillary, and mandibular nerves (Fig. 30-1B).

Figure 30-1 A, Cutaneous distribution of the trigeminal nerve (cranial nerve V). Note that the supraorbital, infraorbital, and mental foramina are all in line just medial to the pupil when the person looks straight ahead. B, Branches of the trigeminal nerve. (Adapted from Eriksson E, ed. Illustrated Handbook in Local Anesthesia. Philadelphia: Saunders; 1980.)

Ophthalmic Nerve

The first division, the ophthalmic nerve (V₁), is the smallest branch of the gasserian ganglion. It leaves the cranium through the superior orbital fissure and has five cutaneous branches:

1. The medial and lateral branches of the supraorbital nerve, which emerge on the face through the supraorbital notch. These two sensory nerves pierce the frontalis muscle and extend to the lambdoid suture on the back of the skull.

2. The supratrochlear nerve, which provides sensation to the medial aspect of the forehead just above the glabella.

3. The infratrochlear nerve.

4. The lacrimal nerve.

5. The external nasal nerve.

Branches of the ophthalmic nerve provide sensation to the forehead, cornea, upper eyelid, structures in the orbit, and the frontal sinuses.

Maxillary Nerve

The second division, the maxillary nerve (V₂), provides sensation to the maxilla and associated structures, including the teeth, periosteum, mucous membranes of the maxillary sinus, nasal cavity, soft and hard palate, lower eyelids, upper lip, and side of the nose. The second division exits the cranium from the foramen rotundum and ultimately enters the face through the infraorbital canal. It terminates as the infraorbital nerve. The infraorbital nerve gives off sensory branches to the lower eyelids, the side of the nose, and the upper lip.

The anatomy of the maxillary nerve is rather complicated because of its numerous branches. The first branch comprises two short sphenopalatine nerves to the pterygopalatine ganglion, also called the Meckel ganglion or the sphenopalatine ganglion. The next two branches of clinical importance are the nasopalatine and the greater (anterior) palatine nerves. The nasopalatine nerve arises from the pterygopalatine ganglion, courses down along the nasal septum, and is transmitted through the anterior portion of the hard palate by way of the anterior palatine canal. This canal is located in the midline approximately 10 mm palatal to the maxillary central teeth and immediately behind the incisors. The nasopalatine nerve provides sensation to the most anterior portion of the hard palate and the adjacent gum margins of the upper incisors. This nerve is rarely blocked in clinical practice, except in dental operations, because it is quite painful as a result of the tightly bound tissues (Fig. 30-2).

Figure 30-2 The anterior third of the palate, from canine to canine, is anesthetized by a local injection near the anterior palatine canal. There may be some overlapping branches of the anterior palatine nerve. Anesthesia of the posterior two thirds of the palate is obtained by a local injection in the area of the posterior palatine foramen. Note: Do not enter the foramen itself because the anesthetic may reach the middle palatine nerve, produce anesthesia of the soft palate, and result in gagging. (Adapted from Eriksson E, ed. Illustrated Handbook in Local Anesthesia. Philadelphia: Saunders; 1980.)

The anterior, or greater, palatine nerve arises from the pterygopalatine ganglion and passes down through the posterior palatine foramen. The posterior palatine foramen is located 10 mm palatal to the third molar and the bicuspid teeth and intermingles with the nasopalatine nerve opposite the cuspid tooth. The greater palatine nerve provides sensation to most of the hard palate, as well as the palatal aspect of the gingiva. It is rarely blocked in the ED (see Fig. 30-2).

The next branch consists of the posterior superior alveolar (PSA) nerve, which courses down the posterior surface of the maxilla for approximately 20 mm, at which point it enters one or several small posterosuperior dental foramina (see Fig. 30-2). This nerve supplies all the roots of the third and second molar teeth and two roots of the first molar tooth. A third branch consists of the middle superior alveolar (MSA) nerve, which branches off about midway within the infraorbital canal and then courses downward in the outer wall of the maxillary sinus (see Fig. 30-2). This nerve supplies the maxillary first and second bicuspid teeth and the mesiobuccal root of the first molar. The last branch consists of the anterior superior alveolar (ASA) nerve, which branches off into the infraorbital canal approximately 5 mm behind the infraorbital foramen, just before the terminal branches of the infraorbital nerve emerge (Fig. 30-2). This nerve descends in the anterior wall of the maxilla to supply the maxillary central, lateral, and cuspid teeth; the labial mucous membrane; the periosteum; and the alveoli on one side of the median line. There is intercommunication among the ASA, MSA, and PSA nerves.

Mandibular Nerve

The third division, the mandibular nerve (V₃), is the largest branch of the trigeminal nerve. It exits from the cranium through the foramen ovale and divides into three principal branches:

1. The long buccal nerve branches off just outside the foramen ovale. It passes between the two heads of the external pterygoid muscle and crosses in front of the ramus to enter the cheek through the buccinator muscle, buccal to the maxillary third molar. The buccal nerve supplies sensory branches to the buccal mucous membrane and the mucoperiosteum over the maxillary and mandibular teeth. The cutaneous branch provides sensation to the cheek.

2. The lingual nerve courses forward toward the midline. It runs downward superficially to the internal pterygoid muscle and passes lingual to the apex of the mandibular third molar. It enters the base of the tongue at this point through the floor of the mouth and supplies the anterior two thirds of the tongue, the lingual mucous membrane, and the mucoperiosteum.

3. The largest of the V₃ branches is the inferior alveolar nerve. It provides sensation to all the lower teeth, although the central incisors, lateral incisors, and buccal aspect of the molar teeth may receive additional sensory innervation. The nerve descends, covered by the external pterygoid muscle, and passes between the ramus of the mandible and the sphenomandibular ligament to enter the mandibular canal. It is accompanied by the inferior alveolar artery and vein, proceeds along the mandibular canal, and innervates the teeth. At the mental foramen the nerve bifurcates into an incisive branch, which continues forward to supply the anterior teeth. It gives off a side branch, the mental nerve, which exits from the mental foramen to supply the skin. The mental foramen is located approximately between the apices of the lower first and second bicuspids, or premolar teeth. This is a useful site at which to perform a nerve block because the mental nerve provides sensation to the skin of the chin and the mucous membrane of the lower lip.

Equipment for Dental and Cranial Nerve Blocks

Extraoral injections can be done easily with a 3-mL Luer-Lok syringe and a -inch, 25- to 27-gauge needle. A needle no smaller than 27 gauge is recommended for deep block techniques because of the inability to perform aspiration. Generally, a long needle is used for nerve blocks and a short needle is used for infiltration. Intraoral local anesthesia can also be conveniently administered with a dental aspirating syringe, which uses a Carpule cartridge of anesthetic along with a disposable needle (Fig. 30-3A). Dental aspirating syringes are not mandatory for intraoral local anesthesia but they make the procedure simpler, particularly when aspirating. Other adjuncts that are helpful in the administration of intraoral anesthesia include topical mucosal anesthetic agents such as gels or sprays because they can make the injection nearly painless (Fig. 30-3B). First swab the gauze-dried mucosa with a topical agent or have the patient hold cotton swabs soaked in the agent to the anticipated injection site, and wait for 1 to 3 minutes. Excellent topical anesthesia of the mucous membranes can be achieved after 2 minutes by applying a gel mixture of a topical anesthetic consisting of 10% lidocaine, 10% prilocaine and 4% tetracaine (Profound, Steven’s Pharmacy, Costa Mesa, CA; www.stevensrx.com).

Figure 30-3 A, Local anesthesia—basic setup for intraoral application using an aspirating dental syringe. B, Topical mucosal anesthesia can make the injection nearly painless. Swab the gauze-dried mucosa with the topical agent or have the patient hold cotton swabs soaked in the agent, and wait for 1 to 3 minutes. Benzocaine can be used as a topical anesthetic (shown here). However, excellent topical anesthesia of mucous membranes can be obtained after 2 minutes by applying a gel mixture of a topical anesthetic consisting of 10% lidocaine, 10% prilocaine, and 4% tetracaine. (Profound, Steven’s Pharmacy, Costa Mesa, CA. Available at www.stevensrx.com).

The anesthetic agent most frequently used is 2% lidocaine with a vasoconstrictor such as epinephrine at a concentration of 1 : 100,000. Many other anesthetic agents, such as mepivacaine (Carbocaine) and Cetacaine (a combination of benzocaine, tetracaine, butamben, and benzalkonium), with or without vasoconstrictor agents, are also available. Bupivacaine (Marcaine 0.5%) with or without epinephrine (1 : 100,000) is a longer-acting anesthetic that is often ideal for procedures performed in the ED. Bupivacaine with epinephrine is theoretically the best choice in the ED because of its longer duration of action. As a result of the rich vascularity of the oral cavity, vasoconstrictors are important in sustaining the duration of anesthesia and should be used whenever possible in the absence of medical contraindications.

General Recommendations

Use needles no smaller than 27 gauge for block techniques because a higher-gauge needle makes aspiration difficult and can thus result in inadvertent intravascular injection. Intravascular epinephrine, though used in small doses, may produce systemic symptoms (anxiety, tachycardia), as well as painful vasospasm if injected intraarterially, but the amount of local anesthetic is generally inconsequential.²

When an intraoral block is performed, the needle should not be inserted to its full length at the hub. Should inadvertent breakage occur in such a situation, retrieval of the needle may be difficult. Furthermore, the direction of the needle should not be changed while the needle is deep in the tissue. Always aspirate before injection, and inject slowly to minimize pain. A warmed anesthetic solution is also more comfortable for the patient. Place topical anesthetics on mucous membranes before all dental blocks to make the needle puncture less painful. This adjunctive measure is greatly appreciated by the patient and suggested whenever possible.

An important caveat for intraoral local anesthesia is that an injection should not be made into or through an infected area. This is especially important with inferior alveolar nerve blocks, in which extension of an infection can be serious and difficult to treat. Trismus with inadequate oral access or direct extension of infection to the parapharyngeal spaces can result. Therefore, local anesthesia should be only superficial before incision and drainage, unless a block can be performed far proximal to the site of infections.

Technique

Topical Anesthesia

Most patients fear dental blocks greatly, and the anxiety and pain may be lessened considerably with the use of topical anesthetics applied to the mucous membranes before injection (Fig 30-4, step 3). It is important to dry the injection site thoroughly with gauze before the injection (see Fig 30-4, step 2) because copious saliva will wash the anesthetic away prematurely. Coat a cotton-tipped applicator generously with 20% benzocaine (Hurricaine, Beutlich, Inc., Niles, IL) or 5% to 10% lidocaine so that the area of injection is completely covered. Allow the patient to hold the cotton swab in place. The area will be anesthetized in 2 to 3 minutes. Use concentrated topical anesthetics because poor results are obtained with weaker preparations such as 2% viscous lidocaine. Cocaine (4%) is another acceptable topical anesthetic.

Figure 30-4 Head and neck regional anesthesia—general technique.

Supraperiosteal Infiltration

The most common technique for intraoral local anesthesia of individual teeth is supraperiosteal infiltration (Fig. 30-5). This technique can provide complete relief of a toothache. Select the area to be anesthetized and dry it with gauze. Apply a topical anesthetic, such as 20% benzocaine or 5% lidocaine ointment, as described. Ask the patient to close the jaw slightly and relax the facial musculature. Grasp the mucous membrane of the area with a piece of gauze. Pull the gauze outward and downward in the maxilla and outward and upward in the mandible to extend the mucosa fully and to delineate the mucobuccal fold. Puncture the mucobuccal fold with the bevel of the needle facing the tooth. Aspirate the area and deposit approximately 1 to 2 mL of local anesthetic (2% lidocaine should be used here) at the apex (area of the root tip) of the involved tooth (see Fig. 30-5). It is helpful to place a finger against the outer aspect of the lip overlying the injection site. Apply firm and steady pressure against the lip and slowly inject the local anesthetic into the supraperiosteal site. This helps prevent ballooning of the lip.

Figure 30-5 Supraperiosteal nerve block. A, Anatomy and distribution. B, Technique. Deposit the anesthetic next to the periosteum at the level of the apex (area of the root tip) of the desired tooth. The palatal side of the tooth may also be injected.

The purpose of the injection is to deposit the anesthetic near the bone that supports the tooth. The anesthetic must penetrate the cortex of bone to reach the nerve of the individual tooth, so the injection may fail if the solution is deposited too far from the periosteum, if the needle is passed too far above the roots of the teeth, or if the bone in the area is unusually thick or dense. If anesthesia is unsuccessful, inject the palatal side. It may take 5 to 10 minutes to achieve full anesthesia with this technique, however, and the procedure may not be as effective for the posterior molars. Infiltration of the area around the maxillary canine and the first premolars will anesthetize the MSA and ASA nerves; lacerations of the upper lip can be treated by bilateral injection in the canine fossa areas.

Posterior or Superior Alveolar Nerve Block

Anatomy

Use the PSA block to anesthetize the maxillary molar teeth (Fig. 30-6). On occasion, the maxillary first molar is not completely anesthetized by this technique alone and may require an additional block (discussed subsequently). The landmarks for this technique are the posterior-lateral portion of the maxillary tuberosity and the second molar.

Figure 30-6 Posterior superior alveolar nerve block. A, Anatomy and distribution. B, Technique. Insert the needle at the upper second molar and direct it toward the maxillary tuberosity to a depth of 2 to 2.5 cm.

Intraoral Approach

For the intraoral approach, apply a topical anesthetic on a cotton-tipped swab to the gauze-dried mucosa for 60 to 90 seconds before introducing the needle for the nerve block.² With the patient’s mouth half-open and the jaw facing the operator, retract the cheek laterally. Make the puncture in the mucosal reflection just distal to the distal buccal root of the upper second molar (Fig. 30-6B). Direct the needle toward the maxillary tuberosity (i.e., upward, backward, and inward) and then along the curvature of the maxillary tuberosity to a depth of approximately 2 to 2.5 cm. On reaching this depth, aspirate with the needle and inject 2 to 3 mL of anesthetic solution.

An infraorbital nerve block can be used to anesthetize the midface region (Fig. 30-9A). A solution of local anesthetic deposited adjacent to the infraorbital foramen anesthetizes not only the middle and superior alveolar nerves but also the main trunk of the infraorbital nerve, which innervates the skin of the upper lip, the skin of the nose, and the lower eyelid. The nasal mucosa is not anesthetized with this technique.

Figure 30-9 Infraorbital nerve block. A, Distribution. B, Anatomy. C, Technique. Needle entry occurs at the upper second bicuspid (premolar); advance the needle parallel to the tooth to a depth of 2.5 cm.

The infraorbital foramen is difficult to palpate extraorally and almost impossible to feel in the presence of facial swelling. It is found on the inferior border of the infraorbital ridge on a vertical (sagittal) line with the pupil when the patient stares straight ahead. Although one volunteer study found similar patient pain scale scores and overall preference in subjects undergoing both intraoral and extraoral approaches, the intraoral approach seemed to provide nearly twice the duration of anesthesia.³

Intraoral Approach

Apply a topical anesthetic on a cotton-tipped swab to gauze-dried mucosa for 60 to 90 seconds before introducing the needle for the nerve block. When performing the intraoral approach, keep the palpating finger in place over the inferior border on the infraorbital rim. Retract the cheek as for the supraperiosteal injection, and make the puncture in the mucosa opposite the upper second bicuspid (premolar tooth) approximately 0.5 cm from the buccal surface (Fig. 30-9B). Direct the needle parallel to the long axis of the second bicuspid until it is palpated near the foramen, at a depth of approximately 2.5 cm. If the entry is too acute, one may encounter the malar eminence before approaching the infraorbital foramen. In addition, if the needle is extended too far posteriorly and superiorly, the orbit may be entered. Halt the procedure if you are unsure of the location of the needle or if the patient is not cooperating.

When the proper needle location has been determined and aspiration has been performed, inject 2 to 3 mL of solution adjacent to, but not within the foramen. Hold a finger firmly on the inferior orbital rim to avoid ballooning of the lower eyelid with anesthetic solution. If you are not certain of the exact location of the infraorbital foramen, perform a field block to obtain anesthesia. For the latter technique, infiltrate 5 mL of the anesthetic solution in a fanlike distribution in the upper buccal fold. This technique is not as precise as a discrete nerve block but usually produces the same effect. Massage the tissue for 10 to 15 seconds after the injection to hasten the onset of anesthesia.

Extraoral Approach

The infraorbital foramen can also be approached from an extraoral route (Fig. 30-10). The extraoral approach requires external preparation of the skin. With the extraoral approach use similar landmarks to locate the infraorbital foramen. The needle can be felt as it passes through the skin, the subcutaneous tissue, and the quadratus labii superioris muscle. After injection, firmly massage the infiltrated tissue for 10 to 15 seconds. It is usually visibly swollen. Place a finger under the eye to limit eye edema.

Figure 30-10 Infraorbital nerve block, external approach. While injecting, place a finger under the eyelid to minimize lid swelling.

Be careful to not anesthetize the facial artery and vein because these vessels may lie on either side of the needle. Do not use vasoconstrictors to avoid vasoconstriction of the facial artery. If severe blanching of the face occurs, warm compresses should be applied to the face immediately. Local phentolamine may also be injected into the blanched area to reverse the ischemia.

Inferior Alveolar Nerve Block

In the setting of extreme dental pain, the emergency clinician may find the inferior alveolar nerve block and the lingual nerve block useful. This injection is somewhat more difficult than the other techniques described, and the emergency clinician is advised to view demonstrations of this procedure before attempting it. The inferior alveolar nerve block provides anesthesia to all the teeth on that side of the mandible and desensitizes the lower lip and chin via blockade of the mental nerve. This technique is primarily useful for anesthetizing patients who have sustained severe dentoalveolar trauma; those with complaints of postextraction pain, a dry socket, or pulpitis (toothache); or those with a periapical abscess.

Anatomy

First review the anatomy of the region (Fig. 30-11A). The patient can be seated either in a dental chair or upright with the occiput firmly against the back of the stretcher so that when the mouth is opened, the body of the mandible is parallel to the floor. Despite the use of topical anesthesia, be ready for an unexpected quick jerk of the head when an anxious patient first feels the needle. Stand on the side opposite the one being injected.

Figure 30-11 Inferior alveolar nerve block. A, Anatomy and distribution. Identify the anterior border of the mandibular ramus (coronoid notch) with the thumb. B, Approach. C, Technique.

The technique first involves palpation of the retromolar fossa with the index finger or thumb. With this maneuver, the greatest depth of the anterior border of the ramus of the mandible (the coronoid notch) may be identified (Fig. 30-11A). With the thumb in the mouth resting in the retromolar fossa and the index finger placed externally behind the ramus at the same height as the thumb (Fig 30-12), the tissues are retracted toward the buccal (cheek) side, and the pterygomandibular triangle is visualized (Fig. 30-11C). This technique also moves the operator’s finger safely away from the tip of the needle.

Figure 30-12 To compensate for difficulty obtaining the correct approach with a straight needle for the inferior aveolar nerve block, a 25-gauge -inch needle is bent 30 degrees with the needle guard.

Approach

Coat the gauze-dried mucosa over the area to be injected with a topical anesthetic, as described previously. When topical anesthesia has been achieved, hold the syringe parallel to the occlusal surfaces of the teeth and angled so that the barrel of the syringe lies between the first and second premolars on the opposite side of the mandible (Fig. 30-11B). Failing to appreciate this required angle is the most common reason for failure of this nerve block. If a large-barrel syringe is used, the corner of the mouth may hamper efforts to obtain the proper angle. Facilitate the angle by carefully bending the 25-gauge needle about 30 degrees (see Fig. 30-12). Puncture inside the triangle at a point 1 cm above the occlusal surface of the molars. If the needle enters too low (e.g., at the level of the teeth), the anesthetic will be deposited over the bony canal and prominence (lingula) that house the mandibular nerve and not over the nerve itself.

The needle can be felt as it passes through the ligaments and the muscles covering the internal surface of the mandible. Stop when the needle has reached bone, which signifies contact with the posterior wall of the mandibular sulcus; bone must be felt with the needle. Failure to do so generally results from directing the needle toward the parotid gland (too far posteriorly) rather than toward the inner aspect of the mandible. This will anesthetize portions of the facial nerve. Withdraw the needle slightly and aspirate. Deposit approximately 1 to 2 mL of solution. Three to 4 mL may be required if needle positioning is suboptimal. In children, the angulation is not parallel to the occlusal surfaces of the teeth. Instead, hold the barrel of the syringe slightly higher because the mandibular foramen is lower.

One may anesthetize the lingual nerve by placing several drops of anesthetic solution while slowly withdrawing the syringe and needle. The anterior two thirds of the tongue can thus be anesthetized. In actual practice, the lingual nerve is consistently blocked with this procedure because of the close proximity of both nerves. Anesthetize the long buccal nerve by injecting 0.2 mL of local anesthetic just distal and buccal to the last mandibular molar. Supplementing the inferior alveolar block with both lingual and buccal nerve blocks helps anesthetize any aberrant fibers that may also be innervating the teeth. Shortly after a successful injection, the patient will report tingling in the lower lip; however, 3 to 5 minutes is usually required to achieve complete anesthesia.

Complications

Complications include inadvertent administration of anesthetic posteriorly in the region of the parotid gland, which will anesthetize the facial nerve. This is an annoying but relatively benign complication that will cause temporary facial paralysis (similar to Bell’s palsy). It will affect the orbicularis oculi muscle and cause an inability to close the eyelid. Should this occur, protect the eye with an eye patch or tape until the local anesthetic has worn off (≈2 to 3 hours). Reassure the patient. Anesthesia with bupivacaine (Marcaine) presents a more significant problem if this complication occurs because bupivacaine anesthesia lasts from 3 to 6 hours (perhaps longer in some patients if epinephrine is used).

Gow-Gates Block

Anatomy

The inferior alveolar nerve block may be unsuccessful because of deposition of anesthetic in a plane medial to the lingula. In addition, the traditional technique involves depositing additional anesthetic for the long buccal nerve. First introduced in the 1970s, the Gow-Gates mandibular block is also an acceptable technique for achieving mandibular anesthesia, especially if traditional approaches fail (Fig. 30-13). The Gow-Gates approach involves the deposition of anesthetic at the lateral aspect of the anterior condylar head below the insertion of the lateral pterygoid muscle, and it uses extraoral landmarks (tragus of the ear and corner of the mouth).⁴ The area is much less vascular than the area near the lingula. For this reason, epinephrine mixed with the local anesthetic is not necessary.

Figure 30-13 Gow-Gates block. A, Distribution. B, Anatomy and approach. Angle the needle from the opposite premolars toward the condylar head. C, Technique. (Adapted from Norton NS. Mandibular injections. In: Netter’s Head and Neck Anatomy for Dentistry. Philadelphia: Saunders; 2007:572-574. Copyright 2007 Elsevier Inc.)

Approach

Ask the patient to open the mouth widely (Fig. 30-13C). Place a finger inferior to the tragus of the ear as the landmark for the lateral aspect of the anterior condyle (which is now sitting at the eminence). Insert the needle opposite the second molar with the barrel of the syringe between the opposite lower premolars and the corner of the mouth (similar to the inferior alveolar approach). With this plane maintained, advance the needle until it reaches the condylar neck. Withdraw the needle, aspirate, and inject 1 to 2 mL of anesthetic.^4,5

Complications

The positive vascular aspiration rate with the Gow-Gates procedure is reported to be 1.6%, as compared with a range of positive aspiration with the conventional inferior alveolar technique of 3.5% to 22%.⁶ If the needle is directed more toward the medial aspect of the anterior condylar process, the needle is then in the proximity of the pterygoid plexus of veins and the sympathetic plexus of the internal carotid artery. If the sympathetic plexus is anesthetized, Horner’s syndrome will temporarily develop.

Mental Nerve Block

Block the mental nerve by infiltrating local anesthetic about the nerve where it exits its bony foramen. Avoid inserting the needle into the mental nerve foramen because the needle or injection of liquid into the foramen can produce neurovascular damage. Infiltrate around the foramen to provide anesthesia of the lower lip. For lacerations over the midline of the lips, administer anesthetic about the mental nerve on each side of the face. This practice anesthetizes crossover fibers. Use a 1.3-cm (-inch), 25- or 27-gauge needle on a 3-mL syringe.

Anatomy

The mental nerve is a continuation of the inferior alveolar nerve and innervates the mucosa and skin of the lower lip on the ipsilateral side of the mandible, with limited crossover of midline fibers. The nerve emerges from the mental foramen below the second premolar. Lacerations of the lower lip can be repaired with this block (Fig. 30-14).

Figure 30-14 A mental nerve block is ideal for a complicated lower lip laceration because it will not distort tissue.

Approaches

Like the infraorbital nerve, block the mental nerve via an intraoral or extraoral approach. Syverud and colleagues found that volunteers who received intraoral topical anesthetic followed by an intraoral injection considered the technique to be less painful than the extraoral approach.⁷ Before using either approach, identify the mental foramen by palpation about 1 cm inferior and anterior to the second premolar. It is usually best to locate the foramen with a gloved finger placed in the labial area over the mandible. Generally, the foramen will be just medial to the pupil of the eye (while the patient stares straight ahead) along a sagittal plane. The intraoral approach is demonstrated in Figure 30-15.

Figure 30-15 Mental nerve block. A, Distribution. B, Anatomy and approach. The mental foramen is found below the second premolar. C, Technique.

With the intraoral approach it is best to use topical anesthesia before infiltration. Anesthetize the lower labial fold adjacent to the first or second premolar. Approach the mental foramen at about a 45-degree angle, and infiltrate the area adjacent to the foramen with 1 to 2 mL of local anesthetic. Massage as described previously.

Scalp Block

Scalp blocks provide surgical anesthesia for repair of scalp lacerations, drainage of superficial scalp abscesses, and exploration and débridement of scalp wounds.

Anatomy

As shown in Figure 30-16, the scalp receives its nerve supply from branches of the trigeminal nerve (fifth cranial nerve) and the cervical plexus. The forehead is supplied by the supraorbital and supratrochlear nerves. Both nerves are branches of the ophthalmic division of the trigeminal nerve. The temporal region receives its nerve supply from the zygomaticotemporal (a V₂ branch nerve), temporomandibular, and auriculotemporal nerves (V₃ branch nerves).

Figure 30-16 Sources of sensory nerve supply to the scalp. Nerves above the blue line become superficial and converge toward the vertex of the scalp.

The posterior aspect of the scalp is innervated by the great auricular and the greater, lesser, and least (third) occipital nerves. The nerves that supply the posterior aspect of the scalp originate from the cervical plexus. All the nerves become superficial above a line drawn from the upper border of the external ear to the occiput and the eyebrows and converge toward the vertex of the scalp (see Fig. 30-16).

Topographically, the nerves and vessels of the scalp are located in subcutaneous tissue above the epicranial aponeurosis. From this level they divide into small branches that extend to the deeper layers (epicranium and periosteum) (Fig. 30-17).^8,9

Figure 30-17 Topographic anatomy of the scalp taken above a line drawn from the upper border of the external ear to the occiput and the eyebrows. Generously infiltrating this area in a fanlike motion will block multiple sensory nerves. (Adapted from Eriksson E, ed. Illustrated Handbook in Local Anesthesia. Philadelphia: Saunders; 1980.)

Approaches

A scalp block can be accomplished by individually blocking each nerve that supplies the scalp, but this approach is time-consuming, difficult, and cumbersome. Because the nerves on the scalp are located superficially, a scalp block can easily be performed by injecting local anesthetic agents into the subcutaneous tissue circumferentially around the area to be blocked. Injection of local anesthetic to deeper levels is necessary only if bone is to be removed. Note that injection of local anesthetic agents only in the deeper layers without subcutaneous infiltration results in an unsuccessful block and a greater amount of bleeding during surgical intervention.

In preparation for the block, clip a band of hair (some clinicians prefer to shave the head, but this procedure is of unproven benefit). A band 1 cm wide and 3 cm away from the wound can be clipped circumferentially. Inject local anesthetic in the clipped area.

Prepare the skin with an antiseptic solution, and raise a skin wheal at any point along the clipped skin with a 1.3-cm (-inch), 25-gauge needle. Insert a 7.6-cm (3-inch), 22-gauge needle through the skin wheal and into subcutaneous tissue. Advance it along the scalp circumferentially following the previously clipped area. Inject 0.5% to 1% lidocaine or 0.125% to 0.25% bupivacaine with epinephrine (1 : 200,000). Add epinephrine to the local anesthetic agent to provide vasoconstriction and prevent excessive blood loss and absorption of local anesthetic. The total dose of the local anesthetic agents should not exceed the recommended dose for that particular agent (see Chapter 29). Inject some local anesthetic solution into the temporalis muscle to prevent contraction of the muscle during the primary procedure if necessary.

Colley and Heavner demonstrated that when bupivacaine is used, peak plasma local anesthetic concentrations occur within 10 to 15 minutes after injection.¹⁰ Thus, the first 10- to 15-minute period after the injection is the most critical period to monitor for local anesthetic toxicity. Colley and Heavner also found that despite the scalp’s high vascularity, absorption of local anesthetics from the scalp is not excessive.¹⁰ Because that the toxic plasma threshold for bupivacaine is 4 µg/mL, these concentrations suggest that a scalp block using bupivacaine has a wide margin of safety, even without the use of epinephrine. When epinephrine is used with bupivacaine, its effect on absorption becomes more pronounced with concentrations of 0.125% than with 0.25%. This is probably because at low concentrations (0.125%), bupivacaine has a vasoconstrictor property.¹¹

Greater and Lesser Occipital Nerve Block

This relatively simple block may be useful in the ED for treating occipital neuralgia and tension headaches. For occipital neuritis, a long-acting corticosteroid such as methylprednisolone (20 to 40 mg) may be combined with the local anesthetic (see Chapter 52).¹²

Anatomy

The posterior aspect of the head is supplied by the posterior rami of the cervical nerves. Two important branches of these nerves are the greater and lesser occipital nerves. The greater occipital nerve becomes superficial on each side at the inferior border of the obliquus capitis inferior muscle and runs superiorly toward the vertex over this muscle. The nerve is located medial to the occipital artery. The lesser occipital nerve is located approximately 2.5 to 3.5 cm lateral and 1 to 2 cm caudal to the greater occipital nerve (see Fig. 30-16).

Approach

It is not usually necessary to shave or clip the scalp before performing greater and lesser occipital nerve blocks. The greater occipital nerve can best be blocked at the nuchal line, which extends from the middle of the external occipital protuberance to the mastoid process. The nuchal line is located between the insertion sites of the trapezius muscle and the semispinalis muscles. At this site the greater occipital nerve is just medial to the occipital artery.

First, palpate the occipital artery. Next, attach a 3.8-cm, 23- to 25-gauge needle to a syringe containing 5 mL of local anesthetic. Insert the needle into the skin (Fig. 30-18A). After obtaining paresthesia at the vertex, inject 5 mL of local anesthetic solution. Block the lesser occipital nerve with a fanlike injection of a local anesthetic solution, 2.5 to 3.5 cm lateral and 1 cm caudal to the point described for the greater occipital nerve (Fig. 30-18B).

Figure 30-18 Occipital nerve blocks. A, Block the greater occipital nerve on a line 3 cm lateral to the external occipital protuberance and the base of the occipital bone. B, Block the lesser occipital nerve by injection of 2 to 3 mL of anesthetic solution along the posterior border of the mastoid process of the temporal bone.

This procedure is not usually associated with any complications; however, intraarterial injections should be avoided by careful aspiration.

Ophthalmic (V₁) Nerve Block

The lateral and medial branches of the supraorbital, supratrochlear, and infratrochlear nerves may be blocked by percutaneous local injection at the point where they emerge from the superior aspect of the orbit. Anesthesia of the forehead and scalp is achieved as far posteriorly as the lambdoid suture. Although anesthesia for suturing lacerations of the forehead and scalp is easily achieved, the nerve block may also be used for débridement or topical treatment of burns or abrasions and for delicate lacerations of the upper eyelid (Fig. 30-19). Such anesthesia is ideal for removing small pieces of glass embedded in the forehead from a windshield injury.

Figure 30-19 An ophthalmic (V₁) nerve block would be ideal for this patient with extensive forehead and eyelid lacerations. Additionally, an infraorbital (V₂) block could be used to provide anesthesia for repair of the maxillary laceration.

Anatomy

The subtle supraorbital notch, which is in line with the pupil (when the patient is staring straight ahead), can be palpated along the superior orbital rim (Fig. 30-20B). This landmark is the site of injection for blockade of the supraorbital nerves. The supratrochlear nerve is found 0.5 to 1.0 cm medial to the notch. The infratrochlear nerve is not usually blocked but is found in the most medial aspect of the superior orbital rim. If the anesthetic is placed on the forehead proper, this block may not produce complete anesthesia of the skin of the upper eyelid if the sensory branches to the eyelid are given off before the supraorbital nerve traverses the forehead.