Head and Neck Blocks

Roderick J. Finlayson

KEY POINTS

1. Awake intubation can be the safest course of action in the presence of a difficult airway (1).

2. Adequate airway anesthesia will enhance patient cooperation and greatly facilitate awake intubation.

3. Sensory innervation of the airway is divided into three zones supplied by the trigeminal, glossopharyngeal, and vagal nerves.

4. Topical anesthesia is sufficient for most clinical situations. However, nerve blocks can provide additional analgesia when, particularly, stimulating procedures are planned.

5. Total local anesthetic doses should be closely monitored during airway anesthesia in order to avoid toxicity.

6. Cervical plexus blocks are commonly used in conjunction with brachial plexus blocks to provide surgical anesthesia and postoperative analgesia for shoulder and clavicle surgeries.

7. Cervical plexus blocks can also be used to provide anesthesia for carotid endarterectomy. Not only do they allow the patient’s neurologic status to be monitored, they also confer greater hemodynamic stability and result in shorter hospital stay than general anesthesia.

8. Superficial and intermediate cervical plexus blocks provide greater safety and efficacy than deep cervical plexus blocks for carotid endarterectomy.

9. Facial nerve blocks can provide anesthesia for minor cosmetic procedures as well as laceration repairs and are particularly suited for pediatric analgesia.

10. Although the three trigeminal branches can be blocked proximally at the pterygopalatine fossa, a distal approach is associated with fewer complications.

I. Airway blocks

A. Anatomy

1. Sensory fibers of the nasal mucosa arise from the middle division of the trigeminal nerve (i.e., cranial nerve V) by means of the sphenopalatine ganglion (Fig. 13.1). The latter lies

under the nasal mucosa posterior to the middle turbinate. Fibers from this ganglion also provide sensory innervation to the superior portion of the pharynx, uvula, and tonsils. These fibers can be anesthetized with transmucosal topical application of local anesthetic.

FIGURE 13.1 Sensory innervations of the airway. The trigeminal nerve (i.e., cranial nerve V) supplies the nasal mucosa, superior portion of the pharynx, uvula, and tonsils; the glossopharyngeal nerve (i.e., cranial nerve IX) supplies the oropharynx, supraglottic regions, and posterior portion of the tongue; and the vagus nerve (i.e., cranial nerve X) supplies the larynx and trachea.

2. The glossopharyngeal nerve (i.e., cranial nerve IX) provides sensory innervation to the oropharynx, supraglottic region, and posterior portion of the tongue (Fig. 13.1). This nerve can be blocked by topical anesthesia or direct submucosal injection of local anesthetic behind the tonsillar pillar.

3. Sensation in the larynx itself above the vocal cords is provided by the superior laryngeal nerve. The latter departs from the main vagus nerve (i.e., cranial nerve X) in the carotid sheath and courses anteriorly, sending an internal branch that penetrates the thyrohyoid membrane. Behind the latter, the nerve subdivides to provide sensory innervation to the vocal cords, epiglottis, and arytenoids (Fig. 13.1).

4. Below the vocal cords, sensory innervation is provided by branches of the recurrent laryngeal nerve, which originates from the vagus nerve. The recurrent laryngeal nerve also provides motor fibers to all but one of the intrinsic laryngeal muscles. Topical (or transtracheal) anesthesia can efficiently anesthetize the recurrent laryngeal nerve.

B. Drugs

1. In order to facilitate transmucosal absorption, higher concentrations of local anesthetics are required for topical anesthesia than for perineural infiltration. As it is readily available and presents a favorable toxicity profile, lidocaine in concentrations of 4% to 10% is commonly used.

2. Although there exists evidence that plasma concentrations are significantly lower with topical application than local infiltration, care must be taken when exceeding a total dose of 300 mg in adult patients. (See section “Complications”)

3. Use of topical vasoconstrictors can be beneficial because they reduce bleeding. A vasoconstricting nasal spray (oxymetazoline 0.05%) can be applied before the local anesthetic, or alternatively, 0.25% phenylephrine can be added to the lidocaine solution.

C. Techniques

1. Topical anesthesia

a. Nasal mucosa. Cotton pledgets soaked in 4% lidocaine on long applicators are inserted bilaterally into both nares and directed posteriorly along the inferior and middle turbinates until they contact the posterior pharyngeal wall and sphenoid bone, respectively (Fig. 13.2). This technique provides anesthesia to the sphenopalatine ganglion, usually within 5 minutes.

b. Mouth and pharynx. A total of 4 mL of 4% lidocaine is placed in an atomizer and the tongue, sprayed with local anesthetic. The patient is then instructed to gargle with the residue. Next, the (anesthetized) tongue is grasped with a dry gauze sponge and gently held with one hand. The patient is then instructed to pant vigorously (like a puppy) whereas the rest of the local anesthetic is sprayed into the posterior pharynx with each inspiration.

c. Trachea. A transtracheal injection can be used to provide tracheal anesthesia (Fig. 13.3). Alternatively, if a fiber-optic bronchoscope is being used to facilitate intubation, a similar volume of 4% lidocaine can be injected through the distal port once the trachea is visualized (2).

2. Nerve blocks

a. Lingual branches of glossopharyngeal nerve. The tongue is retracted medially with a tongue depressor to reveal the inferior curve of the anterior tonsillar pillar (Fig. 13.4). A 25-gauge spinal needle is used to inject 2 mL of 1% lidocaine 0.5 cm below the mucosa at a point 0.5 cm lateral to the base of the tongue itself. The longer length of the spinal
needle will allow easier control by permitting the syringe to remain outside the mouth. Aspiration is performed before injection to detect intravascular placement. Bilateral infiltrations are required to block both lingual branches of the glossopharyngeal nerve.

FIGURE 13.2 Nasal airway anesthesia. Cotton pledgets soaked in local anesthetic are inserted along the inferior and middle turbinates to produce anesthesia of the underlying sphenopalatine ganglion by transmembrane diffusion of the solution. Wide pledgets are needed to provide maximal topical anesthesia and vasoconstriction of the nasal mucosa as well.

b. Superior laryngeal nerve. Patient’s head is extended. The thyroid cartilage and hyoid bone are identified. The index finger retracts the skin down over the superior ala of the thyroid cartilage, and the skin is wiped with an alcohol swab. A 23- or 25-gauge needle connected to a 5-mL syringe filled with 1% lidocaine is inserted into the tip of the cartilage. The index finger then releases the skin traction, and the needle is “walked off” the cartilage superiorly and is inserted just through the firm thyrohyoid membrane. The tip now lies in the loose areolar tissue plane beneath the membrane (Fig. 13.5). After (negative) aspiration, 2.5 mL of 1% lidocaine is injected into the plane beneath the membrane. This sequence is repeated on the opposite side. Alternatively, the needle can be inserted into the posterior (greater) cornu of the hyoid bone and “walked off” the bone (caudad) onto the membrane.

CLINICAL PEARL