Carin A. Hagberg
Innervation of the nasal and oropharyngeal and laryngeal cavities, as well as the trachea, depends on three pairs of cranial nerves: the trigeminal (V), vagus (X), and glossopharyngeal (IX). Consequently, there is no single nerve that can be blocked to produce complete anesthesia. Most of the nasal cavity innervation involves the sphenopalatine ganglion and the ethmoid nerve. Application of long cotton-tipped applicators soaked in 4% lidocaine with epinephrine or cocaine over the nasal mucosa allows a block of the sphenopalatine ganglion (applicator angled at 45° to the hard palate) and the anterior ethmoid nerve (applicator parallel to the dorsal surface of the nose).
The glossopharyngeal nerve provides sensory innervation of the oropharynx, including the posterior third of the tongue, anterior surface of the epiglottis, posterior and lateral walls of the pharynx, and the tonsillar pillars. The glossopharyngeal nerve also provides motor innervation to the stylopharyngeus muscle, involved in deglutition. The rest of the pharynx, as well as the upper larynx, vocal cords, and trachea, are innervated by the vagus nerve and its branches, especially the superior laryngeal and the recurrent laryngeal nerves.
Preparation of the patient includes the use of 0.4 to 0.8 mg intravenous (i.v.) glycopyrrolate administered 30 to 45 minutes prior to application of the local anesthetic to decrease the amount of secretions and the use of a vasoconstrictor for the nasal mucosa (1% phenylephrine) in the absence of contraindications.
The performance of airway blocks requires that the following be taken into consideration:
1. Adequate preparation, including a complete explanation to the patient and the surgeon of the reason for performing the airway nerve blocks, is essential for patient cooperation and comfort and for success of the procedure.
2. The risk-to-benefit ratio has to be established. The following should be considered: (a) an alternative plan, including the direct spray of local anesthetic solution using 4% lidocaine or 14% to 20% benzocaine (risk of methemoglobinemia) or indirect spray with a nebulizer using 4% lidocaine; (b) the time available; and (c) the patient's condition, including level of consciousness and degree of respiratory depression and insufficiency.
3. The use of appropriate sedation using usually a combination of 2 to 5 mg midazolam and 50 to 150 mg fentanyl to maintain patient comfort. However, sedation should be individually titrated so that verbal contact with the patient is maintained (oversedation may lead to hypoventilation, oxygen desaturation, and respiratory arrest).
4. These blocks should be practiced as much as possible in nonemergency situations to gain experience in performing airway blocks (often required for awake intubation), so that when their success is required for a difficult intubation or when an emergency arises, they can be performed appropriately.
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A. Glossopharyngeal Nerve Block (Anterior Approach)
Patient Position: Supine.
Operator Position: The physician is situated on the contralateral side of the patient's head.
Indications: Abolition of the gag reflex or hemodynamic response to laryngoscopy.
Needle Size: 25-gauge spinal needle.
Local Anesthetic Solution: 2% lidocaine.
Volume: 2 to 4 mL per side.
Anatomic Landmarks: The glossopharyngeal nerve, which emerges from the skull through the jugular foramen, travels along the lateral wall of the pharynx.
Approach and Technique: With the patient's mouth wide open, a tongue blade held with the nondominant hand is introduced in the mouth to displace the tongue medially, creating a gutter between the tongue and the teeth. The gutter ends posteriorly in a cul-de-sac formed by the base of the palatoglossal arch. A 25-gauge spinal needle is inserted at the base of the cul-de-sac and advanced slightly (0.25 to 0.5 cm). After negative air and blood aspiration tests, 2 mL of 2% lidocaine is injected. The procedure is repeated on the other side (Fig. 19-1).
Figure 19-1. A 25-gauge spinal needle is inserted at the base of the cul-de-sac and advanced slightly.
1. The use of a tongue blade may be facilitated by prior application to the mouth of a topical anesthetic solution. Also, 2% lidocaine jelly may be used, spread directly on the tongue blade.
2. If air is aspirated, the needle needs to be withdrawn until no air can be aspirated.
3. If blood is aspirated, it is usually arterial (carotid artery), because the needle is too posterior and too lateral. The needle needs to be redirected medially.
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B. Superior Laryngeal Nerve Block
Patient Position: Supine, head slightly extended.
Operator Position: The physician is situated on the ipsilateral side of the neck.
Indications: Abolition of the gag reflex or hemodynamic responses to laryngoscopy.
Needle Size: 22-gauge, 25-mm hypodermic needle.
Local Anesthetic: 2% lidocaine with epinephrine.
Volume: 2 to 4 mL.
Anatomic Landmarks: The superior laryngeal nerve supplies the sensory innervation of the larynx down to but excluding the vocal cords. At its origin, it travels with the vagus deeply to the carotid artery, before becoming anterior. At the level of the cornu of the hyoid, it divides into an internal sensory branch and an external motor branch to the cricothyroid muscle. The internal branch pierces the thyrohyoid membrane along with the laryngeal artery and vein and splits into two branches. The ascending branch supplies the epiglottis and the vestibules of the larynx, whereas the descending branch supplies innervation to the mucosa at the level of the vocal cords (Fig. 19-2A).
Approach and Technique: The cornu of the hyoid bone is palpated transversally with the thumb and index finger on the side of the neck immediately beneath the angle of the mandible and anterior to the carotid artery. To facilitate its identification, the hyoid bone is displaced toward the side being blocked. One hand displaces the carotid artery laterally and posteriorly. With the other hand, a 23-gauge, 25-mm needle is walked off the cornu of the hyoid bone in an anterocaudal direction, aiming in the direction of the thyroid ligament. At a depth of 1 to 2 cm, 2 mL of 2% lidocaine with epinephrine is injected after negative air and blood aspiration (Fig. 19-2B). The block is repeated on the opposite side.
Figure 19-2. A: Anatomic landmarks. B: Lidocaine with epinephrine is injected after negative air and blood aspiration.
1. Exercise caution not to insert the needle into the thyroid cartilage, since injection of local anesthetic at the level of the vocal cords may cause edema and airway obstruction.
2. If air is aspirated, the laryngeal mucosa has been pierced and the needle needs to be retrieved.
3. If blood is aspirated (superior laryngeal artery or vein), the needle needs to be redirected more anteriorly. Pressure should be applied to avoid hematoma formation.
4. If laryngeal evaluation is performed for vocal cord movement, only the internal laryngeal nerve needs to be blocked. For this purpose, the patient is asked to open the mouth widely. The tongue is depressed with a tongue blade and pulled medially. A Krause forceps with cotton soaked with 4% lidocaine is placed over the lateral posterior curvature of the tongue (along with the downward continuation of the tonsillar fossa) until resistance is met. The forceps should remain in this position for 5 minutes, and the same procedure is then repeated on the opposite side.
5. In case of a bronchoscopy or an awake intubation, the superior laryngeal and the recurrent laryngeal nerves need to be blocked.
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C. Recurrent Laryngeal Nerve Block
Patient Position: Supine with the neck hyperextended.
Indications: Awake laryngoscopy and intubation.
Needle Size: 22-gauge, 35-mm plastic cannula mounted over a needle.
Volume: 3 to 4 mL of 4% lidocaine.
Anatomic Landmarks: The right recurrent laryngeal nerve originates at the level of the right subclavian artery and loops around the innominate artery on the right and the aortic arch on the left. This nerve supplies the sensory innervation of the vocal cords and the trachea, as well as motor innervation to the vocal cords.
Approach and Technique: The cricothyroid membrane is located, and a small amount of local anesthesia is administered subcutaneously using a tuberculin syringe filled with 1% lidocaine (Fig. 19-3A). The nondominant hand is used to identify the cricothyroid membrane and to hold the trachea in place by placing the thumb and third finger on either side of the thyroid cartilage. A 10-mL syringe containing 2% lidocaine, mounted on a 22-gauge, 35-mm plastic catheter over a needle, is introduced into the trachea through the cricothyroid membrane at an angle of 45° in a caudal direction. Immediately after the introduction of the catheter into the trachea, a loss of resistance and the ability to aspirate air should occur. The catheter is advanced into the lumen of the airway and the needle is removed. The syringe is reattached and it should be confirmed that air can be aspirated (Fig. 19-3B). The patient is then asked to take a deep breath. At the end of the inspiratory effort, 3 to 4 mL of local anesthetic solution is injected into the trachea.
Figure 19-3. The cricothyroid membrane is located and a small amount of local anesthesia is administered subcutaneously using a tuberculin syringe.
1. The patient needs to be informed that the injection of local anesthetic solution will likely make him or her cough.
2. This block is contraindicated in patients diagnosed with an unstable neck, because it induces coughing.
3. During performance of the block, the patient should not talk, swallow, or cough, if possible.
4. The catheter should be left in place until the intubation is completed for the purpose of injecting more local anesthetic, if necessary, and to decrease the likelihood of subcutaneous emphysema.
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