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Regional Anesthesia of the Head and Neck
Emergency physicians encounter patients with dental pain, facial lacerations, and other injuries of the head on a regular basis. The assessment of these injuries can be both time consuming and painful. Thankfully, regional anesthesia for these conditions is easy to instill, reliable, and safe. Techniques such as nerve blocks can be used for patient comfort during repair of lacerations of the face, ear, forehead, and, particularly, the lips. A block avoids direct infiltration into the actual laceration, which preserves the anatomy in these delicate areas and thus allows better cosmetic repair.
Nerve blocks can also be used to give patients with dental pain almost immediate relief. They can be used to treat dentalgia caused by infection, fracture, or dry socket. They decrease the need for narcotic drugs. The ability of an emergency physician to master these blocks leads to fast and efficient patient care as well as improved patient satisfaction ( Table 30.1 ).
TABLE 30.1
Nerve Blocks and Indications
| Nerved blocked or area injected | Area anesthetized |
|---|---|
| Supraperiosteal infiltration | Individual teeth |
| Posterior superior alveolar nerve | Second and third molars and partial anesthesia of first molar |
| Middle superior alveolar nerve | First and second premolars, as well as partial anesthesia of first molar |
| Anterior superior alveolar nerve | Central incisor to the canine |
| Infraorbital nerve | Midface region, skin of lateral nose, lower eyelid, and MSA and ASA regions |
| Inferior alveolar nerve | All ipsilateral mandibular teeth, lower lip, and chin |
| Mental nerve | Mucosa and skin of lower lip and chin |
| Scalp block | Skin of the scalp within the blocked area |
| Greater and lesser occipital nerve | Occipital region of the scalp |
| Ophthalmic nerve | Skin of the forehead and scalp (as far back as lambdoid suture), upper eyelid |
ASA, Anterior superior alveolar; MSA, middle superior alveolar.
Anatomy of the Trigeminal Nerve (Cranial Nerve V)
Sensation to the face and head region is supplied primarily by cranial nerve V (CN V), which is also known as the trigeminal nerve, due to its three large branches: V1, the ophthalmic nerve; V2, the maxillary nerve; and V3, the mandibular nerve ( Fig. 30.1 A ). This is the largest of the 12 cranial nerves, originating at the upper portion of the pons. CN V contains motor neural fibers that control the muscles of mastication. This chapter focuses on its sensory function (see Fig. 30.1 B ).
The ophthalmic nerve, V1, courses through the cavernous sinus and exits through the supraorbital fissure. It then gives off three branches: the frontal, lacrimal, and nasociliary (see Fig. 30.1 C ). These nerves and their branches innervate the eye, orbit, forehead, and portions of the nose.
The maxillary nerve, V2, exits through the foramen rotundum and gives off several branches, including the infraorbital nerve and the posterior, middle, and anterior superior alveolar nerves (see Fig. 30.1 C ). These nerves innervate the face, lip, maxillary teeth, and mucosa.
The mandibular nerve, V3, exits through the foramen ovale into the infratemporal fossa. It then splits into many branches that supply the dura and muscles of mastication (motor function), as well as the buccal branch and the auriculotemporal, lingual, and inferior alveolar branches (see Fig. 30.1 C ). These branches supply sensation to the skin on the side of the head, the auricle of the ear, the tongue, the mucosa and skin of the cheek, the mandibular teeth, and the lower lip.
Equipment for Facial Nerve Blocks
The equipment needed to perform facial nerve blocks is very minimal, and should be available in any emergency department (ED) ( Review Box 30.1 ). Medications include common anesthetics such as lidocaine or bupivacaine, with or without epinephrine. The practitioner should always be aware of the maximum doses of anesthetic agents being utilized, although most blocks will require much less than the maximum dosing. Standard 25- to 27-gauge needles are recommended. Using a smaller needle can lead to false-negative aspiration in the case of an arterial puncture. Some of the equipment listed in Review Box 30.1 might not be necessary for all blocks, and some can be substituted. For instance, a tongue depressor is recommended for use as a retractor, but any other acceptable instrument or even a finger can be used for this purpose.
General Recommendations
Some general recommendations apply to nearly all types of blocks ( Fig. 30.2 ). These procedures have very few contraindications. One of them involves infected tissue: the needle should never be inserted through infected tissue because this approach could result in inoculation of deep tissue with bacteria. In addition, patients with an allergy to the anesthetic agent should not undergo these procedures unless an alternative agent is available. Although not an absolute contraindication, coagulopathy might present a higher risk for hematoma and bleeding complications, so, as for any procedure, the risks should be considered and might outweigh the benefits.
When performing many of these blocks, inserting the needle with the bevel facing toward the bone allows the anesthetic to be injected as close to the nerve or bone as possible and increases the likelihood that the procedure will be successful. During and after injection, particularly when working in areas near the lip, slight exterior pressure and massage not only help the anesthetic diffuse to its target but also help prevent ballooning of the lip or facial tissue. Finally, it is generally recommended that the full length of the needle should not be inserted into the mucosa when performing an intraoral injection, so that it can be retrieved if it breaks.
Application of a topical anesthetic before insertion of the needle is not a necessary step prior to inducing any of the intraoral blocks, but it can increase patient comfort ( Fig. 30.3 ). To apply a topical anesthetic, first dry the tissue with gauze and then apply a topical mucosal anesthetic, for instance, viscous lidocaine. Another technique is to soak a piece of gauze with the anesthetic and then place it over the dry mucosa. Spray anesthetics such as cetacaine are popular and effective alternatives to lidocaine-soaked gauze.
Supraperiosteal Injection
Indication
Supraperiosteal injection is generally used to achieve anesthesia of individual maxillary teeth, but it can be used for any tooth. This block works well if the anesthesia is needed for only one or two teeth, and it can be very helpful to alleviate pain associated with a simple toothache. As noted previously, care should be taken to avoid inserting the needle through any infected tissue.
Anatomy
The nerves for each individual tooth enter at the apex of that tooth and are protected by the bone supporting the tooth. Supraperiosteal injection is designed to anesthetize a single tooth ( Fig. 30.4 A ).
Approach
Begin by applying a topical anesthetic, as previously described. Once the anesthetic has had time to take effect, retract the lip until the tissues are taut (down and out for maxillary teeth and up and out for mandibular teeth). Insert the needle at the mucobuccal fold, with the bevel facing the tooth. The needle needs to be inserted only a few millimeters (see Fig. 30.4 B ). Intraarterial injection is unlikely in this block, but you should aspirate prior to slowly injecting 1 or 2 mL of anesthetic. Apply slight pressure and massage as previously discussed. Because the anesthetic needs to penetrate the bone, a few minutes are needed for anesthesia to occur.
Complications
Complications with this injection are very rare. The risk of inoculating deeper tissues with bacteria is possible if the injection goes through infected tissue. Anesthesia can fail if the injection is too high, too low, or too far away from the nerve.
Posterior Superior Alveolar Nerve Block
Indication
The posterior superior alveolar nerve (PSAN) block can be used to provide anesthesia for the first through the third maxillary molars. However, it is likely that only partial anesthesia of the first molar will be achieved due to its innervation with accessory nerves, particularly at the mesiobuccal root of this molar.
Anatomy
The PSAN branches from the maxillary branch of the trigeminal nerve and travels inferiorly just before the maxillary nerve enters the infraorbital groove. The nerve descends along the posterior lateral portion of the maxillary tuberosity and gives off branches to the second, third, and partially the first maxillary molars ( Fig. 30.5 A ).
Approach
Two techniques for creating a PSAN block have been well described in the literature. The traditional method begins similar to the other blocks, that is, by applying a topical anesthetic to the mucosa. The insertion point for the needle is just distal to the root of the second molar, at the height of the mucobuccal fold (see Fig. 30.5 B ). For this block, because of the posterior and medial location of the nerve complex, insert the needle in an upward, inward, and posterior direction (toward the maxillary tuberosity), approximately 45 degrees in each direction. Ultimately, the needle should be inserted approximately 15 mm and certainly no more than 25 mm. The operator should not feel any resistance while inserting the needle and should not encounter bone. If resistance or bone is felt, withdraw the needle nearly and then redirect it. Once the appropriate depth is reached, aspirate and, if negative, slowly inject 1 to 3 mL of anesthetic.
The second technique involves a curved 24-mm needle, to approach the posterior maxillary surface. Again, anesthetize the mucosa with a topical anesthetic. The insertion point for the needle is more posterior than the traditional approach, just distal to the third molar, at the corner of the posterior lateral portion of the maxilla and directed along the posterior maxilla. Insert the needle 10 to 12 mm from the initial insertion point along the posterior wall of the maxilla, and orient it just slightly medially. After aspirating, inject 1 to 3 mL of lidocaine.
In a study of 200 patients undergoing extraction of the second and third molars, Thangavelu and colleagues achieved successful anesthesia with the curved needle technique in all cases at 10 minutes, with no complications. In contrast, after a randomized, controlled comparison of the straight-needle and bent-needle techniques, Singla and Alexander concluded that use of a straight needle was more successful in achieving anesthesia.
Complications
Diplopia and a presentation resembling Horner syndrome (ptosis, enophthalmos, miosis), thought to be caused by diffusion of the anesthetic superiorly and medially to the orbital nerves, were reported in a case series. Isolated fourth cranial nerve (trochlear) palsy has also been reported and seems to be very rare. All these complications were temporary. Visual disturbances are uncomfortable and disturbing for patients but do not appear to be permanent.
The pterygoid plexus can be damaged by a needle that is too long; therefore the use of shorter needles is recommended. Based on a literature review, Singla and Alexander recommended insertion to approximately 15 mm; however, this is lower than many recommendations and up to 25 mm, no deeper, may be required. The further the needle is inserted, the greater the risk of complications.
Middle Superior Alveolar Nerve Block
Indication
The middle superior alveolar nerve (MSAN) block can be used to anesthetize the lateral upper lip and the first and second premolars simultaneously, as well as the mesiobuccal root of the first molar. This technique can be especially useful if the lateral lip is not anesthetized by an infraorbital nerve block.
Anatomy
The MSAN descends posteriorly to anteriorly along the lateral maxillary wall as an extension of the maxillary nerve. The landmark needed for this procedure is the junction between the first molar and the second premolar ( Fig. 30.6 A ). A subset of patients have an anatomic variant in which the MSAN does not exist.
Approach
Begin as you would for any of the other intraoral block procedures, by applying topical anesthetic. Retract the upper lip and pull the tissues taut. Direct the needle toward the intersection of the first molar and the second premolar at the mucobuccal fold, and insert it 5 to 10 mm at a 45-degree angle posteriorly, with the bevel facing the bone, in an effort to place as much anesthetic near the nerve as possible (see Fig. 30.6 B ). Slowly inject 1 to 3 mL of anesthetic while massaging the tissue.
Complications
Complications of this procedure are few: they are the same complications inherent to all procedures, such as bleeding. Because this is an area with low vascularity, hematoma formation and arterial aspiration are rare. For patients with the anatomic variation of absence of the MSAN, this block will obviously fail, so an infraorbital nerve block, an anterior superior alveolar nerve (ASAN) block, or a PSAN block will be necessary, depending on the region needing anesthesia.
Anterior Superior Alveolar Nerve Block
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