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.

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

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).

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.

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.