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Chapter 19. Regional and Topical Anesthesia for Awake Endotracheal Intubation

A 56-year-old woman with a history of neck radiation and difficult intubation is scheduled for a laparoscopic cholecystectomy. An awake oropharyngeal intubation with nerve blocks is planned. Blockade of which cranial nerve would best anesthetize the vocal cords?

A. Glossopharyngeal nerve

B. Hypoglossal nerve

C. Trigeminal nerve

D. Vagus nerve

D is correct. The larynx is innervated by the vagus nerve (Figure 19–1). Above the vocal cords (base of tongue, posterior epiglottis, aryepiglottic folds, and arytenoids), the internal branch of the superior laryngeal nerve (a branch of the vagus nerve) supplies innervation. For the vocal cords and below the vocal cords, the recurrent laryngeal nerve (a branch of the vagus nerve) is the supplier.

A is incorrect. The glossopharyngeal nerve provides innervation to the pharynx, posterior third of the tongue, fauces, tonsils, vallecular, and anterior surface of the epiglottis.

B is incorrect. The hypoglossal nerve does not innervate the pharynx or larynx.

C is incorrect. A branch of the trigeminal nerve (the lingual nerve) innervates the anterior two-thirds of the tongue.

Figure 19–1

Innervation of the larynx.

(Images from NYSORA Continuing Medical Education.)

What are the relevant landmarks for a superior laryngeal nerve block?

A. The palatoglossal and palatopharyngeal arches

B. The hyoid bone and thyroid cartilage

C. The thyroid cartilage and cricoid cartilage

D. The angle of the jaw and the mastoid process

B is correct. To perform the block using the external approach, the patient is placed in the supine position and will need a degree of neck extension to facilitate identification of the hyoid bone. Once identified, the hyoid bone is gently displaced to the side where the block is to be performed and a 25-gauge needle is inserted from the lateral side of the neck, aiming toward the greater cornu. Once contact has been made, the needle is walked off the bone inferiorly, and injecting 2 mL of 2% lidocaine here will block both the internal and the external branches of the superior laryngeal nerve (Figure 19–2). If the needle is advanced a few millimeters, it will pierce the thyrohyoid membrane, and a “give” is felt. Injecting local anesthetic here will result in only the internal branch of the superior laryngeal nerve being blocked. As with all blocks, careful aspiration must ...

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