Benzonatate

The success or failure of an office-based procedure in the upper aerodigestive tract hinges on patient comfort. An inadequately anesthetized patient is apt to be uncomfortable, anxious, and hyperresponsive and therefore unlikely to tolerate the procedure. Conversely, a patient who is well informed, reassured, and thoroughly anesthetized can undergo any of the procedures described in this supplement. Topical anesthesia can be successfully achieved prior to almost all endoscopic procedures of the larynx, trachea, and esophagus.

Unfortunately, many otolaryngologists are not well versed in the methods of delivering topical anesthetics to the upper aerodigestive tract. In the late 1950s, general anesthesia began to supplant local anesthesia as the method of choice for direct laryngoscopy. (1) With this shift, the administration of topical anesthesia to the laryngopharynx gradually became a lost art. In the past 10 years, however, clinic-based procedures of the larynx have undergone a minor renaissance, thanks largely to the skill and effort of Bastian, (2) Ford, (3) Blitzer, (4) and others. More recently, the advent of office-based flexible esophagoscopy has further expanded the armamentarium of office-based procedures for otolaryngologists. (5)

General principles of topical anesthesia

It is interesting that the techniques for delivering topical anesthesia to the laryngopharynx and esophagus have not changed much over the past 50 years. Yet when an otolaryngologist begins to incorporate these techniques into practice, he or she can expect to face a steep learning curve with respect to some procedures--especially with injection laryngoplasty for vocal fold paralysis.

Ideal candidates. It is best to choose "ideal" candidates for the first 5 or 10 procedures until one achieves a level of comfort. In our experience, most patients are reasonable candidates for office-based laryngoesophageal procedures. Several criteria can be used to identify ideal candidates:

Gag reflex. The patient must tolerate a fiberoptic nasopharyngeal endoscopic examination without gagging. Monitoring with a fiberoptic endoscope is key to maintaining visualization, and a hyperresponsive gag reflex may make examination, treatment, and monitoring impossible. However, it should be noted that gagging in the presence of a mirror or rigid transoral endoscope is not a contraindication.

Oral passageway. The patient must have an adequate oral opening ([greater than or equal to] 2 cm interincisor distance) if transoral instrumentation is to be used.

Nasal patency. The patient must have a patent nasal airway at least unilaterally to allow for the passage of the fiberoptic examination scope. Approximately 3 to 4 mm is required for a nasopharyngoscope and slightly more than 5 mm for a transnasal esophagoscope.

Patient cooperation. The patient must be able to remain reasonably still and upright in the examination chair for the duration of the procedure, which typically takes 5 to 15 minutes. Patients with severe torticollis or head tremor are sometimes difficult to treat.

Pain tolerance. Ideal candidates have a reasonable tolerance for pain.

Cautions. Two important cautions should be taken before performing an office-based laryngoesophageal procedure. They concern anticoagulant drugs and anxiety:

Anticoagulants. Ideally, patients who are taking acetylsalicylic acid, a nonsteroidal anti-inflammatory drug, or warfarin would stop their medication prior to any biopsy or injection. However, clinical experience has shown that almost all patients who remain on therapy appear to do well. (2) In fact, we have used 1.8-mm biopsy forceps on dozens of patients who were taking warfarin and noted no episode of prolonged bleeding.

Injection laryngoplasty does pose a risk of postprocedure bleeding into the paraglottic space and occasionally into Reinke's space, and this can lead to prolonged dysphonia. A theoretical risk of hematoma and airway swelling is also present. Patients who cannot discontinue their anticoagulant should be informed of these risks.

Anxiety. Obviously, a patient's anxiety level must be taken into account when determining his or her suitability for a clinic-based procedure. Some anxious patients benefit from taking a 2- to 5-mg dose of diazepam 30 minutes before the procedure. However, the administration of an anxiolytic will necessitate monitoring the patient with pulse oximetry during the procedure.

Patient participation. A methodical approach to informing the patient about each procedural step before it occurs can also help alleviate anxiety. When manipulation of the larynx is performed, the patient should be instructed to "concentrate on your breathing" during this portion of the procedure. This advice can also be quite successful in patients who have a hyperresponsive gag reflex. Slow, shallow breathing minimizes the abductive effects of deep inspiration.

Some patients prefer to hold their tongue with a gauze pad themselves rather than having the surgeon do it. Focusing on such a task may serve as a useful distraction. Some patients like to view the monitor during a procedure, and they experience something akin to biofeedback.

Anatomy of sensory innervation

The sensory nerves of the larynx, trachea, and esophagus are derived from the vagus nerve. Sensation to the glottic and supraglottic structures is supplied by the internal branch of the superior laryngeal nerve (SLN), and subglottic sensory innervation is provided by the recurrent laryngeal nerves. The trachea and esophagus receive sensory innervation from branches of the vagus nerve distally.

The internal branch of the SLN pierces the thyrohyoid membrane at a point halfway between the hyoid bone and the superior border of the thyroid cartilage, and roughly halfway between the thyroid notch and the superior cornu of the thyroid cartilage. The entry point of the SLN through the thyrohyoid membrane can be located for SLN nerve blocks in certain cases, (4) but the vast majority of patients achieve excellent results with topical anesthesia alone.

Topical anesthetization of the larynx and trachea

The administration of topical anesthesia prior to a laryngeal or tracheal procedure (e.g., injection or biopsy) should be performed in the following sequence:

Step 1. Administer topical 2% oxymetazoline/tetracaine spray to the nasal cavities.

Step 2. Spray topical benzocaine/tetracaine onto the palate and posterior pharynx.

Step 3. Drip 3 to 5 ml of 4% lidocaine onto the tongue base and larynx under fiberoptic guidance.

If an overactive gag reflex is a problem, some patients respond to the addition of 1 or 2 100-mg perles of the antitussive benzonatate dissolved in the oral cavity (see "Topical anesthetization of the esophagus," below). Benzonatate is closely related to the amide anesthetics such as tetracaine, and it rapidly induces profound anesthesia in the oropharynx.

Step 3 can be performed with the aid of a videocart monitoring system (video tower) (figure 1). A distal-chip camera or video camera is attached to a fiberoptic scope, and an assistant inserts the scope through the nasal cavity (typically on the patient's left side). Paramedical office personnel can be trained to manipulate the scope. The scope is generally maintained slightly below the palate so that the tongue base and larynx can be easily viewed on a video monitor. The patient is bent forward at the waist with the neck extended in a "sniffing" position to maximize laryngeal exposure (figure 2). Using the left hand, the surgeon grasps the tongue with a 4 x 4-inch gauze pad. A 5-ml syringe of 4% lidocaine attached to an Abraham cannula is advanced into the oropharynx. Approximately 1 ml is deposited over the tongue base, and 2 to 4 mi is dripped onto the vocal folds during phonation, which produces the characteristic "laryngeal gargle" described by Hogikyan (figure 3). (6) It is best to deposit the lidocaine in several 0.5- to 1-ml aliquots instead of in one large dose. Following the initial dose, the patient will usually cough briskly as the anesthetic is aspirated and distributed over the laryngotracheal mucosa. An absence of the laryngeal gargle and cough may indicate that the patient has swallowed the anesthetic. If so, additional topical applications may be indicated.

[FIGURES 1-3 OMITTED]

This procedure is also adequate for delivering tracheal anesthesia, although there is an alternate method. The alternative is to puncture the cricothyroid membrane with a 27-gauge needle and instill 2 to 4 ml of 4% lidocaine transtracheally. Aspiration for air to confirm intraluminal needle position is essential prior to injecting transtracheal lidocaine. If the patient has a tracheostomy tube, all that is necessary is to remove the tube and administer the lidocaine through the stoma. This is especially helpful when evaluating patients with subglottic/tracheal stenosis. Another option is to deliver the lidocaine via the working channel of a fiberoptic endoscope.

Sufficient anesthesia occurs within 90 seconds of topical administration. Lidocaine can be expected to provide 45 to 60 minutes of anesthesia, but benzocaine/tetracaine wears off after 20 to 30 minutes. If a procedure in a patient who has been anesthetized with benzocaine/tetracaine should exceed 20 minutes, the patient may begin to gag when sensation to the palate and oropharynx returns. A reapplication of the spray is generally all that is needed to restore anesthesia.

Topical anesthetization of the esophagus

Preparing a patient for transnasal esophagoscopy can be achieved quite effectively with nasal anesthesia alone. After determining which of the patient's nostrils is more patent, the surgeon simply sprays it with a 1:1 solution of 0.05% oxymetazoline and 4% lidocaine and then packs the area with cotton pledgets soaked with the same solution. Other agents (e.g., 10% cocaine) may also be used.

In the past, patients would receive 2 100-mg benzonatate perles, which they kept on the tongue until the perles dissolved. Our experience, however, suggests that this probably results in excessive hypopharyngeal anesthesia, leading to aspiration of secretions. Therefore, we no longer use benzonatate perles routinely. One benzonatate perle can be used for patients who are undergoing a biopsy or a longer procedure. If any oropharyngeal anesthesia is required (it is usually not), 1 spray of 20% benzocaine can be delivered to the oropharynx.

Adverse reactions to local anesthesia

Drug reactions are always a concern, but they are quite uncommon when basic safety guidelines are followed. Obviously, it is important to adhere to guidelines governing maximum doses (table). (7,8) Excessive use of any anesthetic agent can result in systemic toxicity and lead to cardiovascular depression, convulsions, and respiratory or cardiac arrest. Caution should be exercised when using combinations of different local anesthetics because their potential toxic side effects may be additive. Toxicity can also be potentiated in patients with renal or hepatic compromise and certain cardiac conditions.

Allergic reactions are uncommon with lidocaine, but they may be more prevalent with the esters such as tetracaine and benzocaine. When they occur, allergic responses are typically limited to urticaria and rash; anaphylaxis is very rare. Another rare complication is methemoglobinemia, which leads to an impairment of oxygen delivery to tissues and causes "chocolate cyanosis," a brown discoloration of the lips and mucosa of the oral cavity. A blood methemoglobin level higher than 70% can result in serious cardiac or central nervous system damage. Treatment for methemoglobinemia is 1 to 2 mg/kg of intravenous methylene blue. (9)

Vasovagal syncope occasionally occurs during laryngotracheal and esophageal office procedures. (10) Precipitating factors include anxiety, diffusion of anesthetic to the sympathetic trunk, and strong vagal stimulation from the procedure itself. Affected patients often experience prodromal nausea, sweating, lightheadedness, and paresthesias seconds to minutes before syncope occurs. If this prodrome does occur, the procedure should be discontinued and the patient should assume a reclining or supine position or place the head between the legs. If syncope occurs, the patient should be maintained in a horizontal position until he or she recovers consciousness (typically seconds later). In either case, vital signs should be monitored throughout the episode.

Monitoring requirements

Because anesthesia is induced without the need for sedation, monitoring equipment and intravenous lines are generally not needed. However, common sense dictates that certain particularly ill or medically fragile patients with severe underlying pulmonary disease and/or supplemental oxygen requirements should be monitored with pulse oximetry at the very least. These patients may be better suited for the operating room under monitored anesthesia care.

Postprocedure patient instructions

Because patients are at risk for aspiration, we routinely instruct them to take nothing orally for 45 to 60 minutes following the procedure or until full sensation in the throat returns. Significant postoperative pain is uncommon, and acetaminophen is usually all that is necessary.

References

(1.) Jako GJ. Laryngeal endoscopy and microlaryngoscopy. In: Paparella MM, Shumrick DA, eds. Otolaryngology. Ch. 31. Philadelphia: W.B. Saunders, 1980:2413.

(2.) Bastian RW, Delsupehe KG. Indirect larynx and pharynx surgery: A replacement for direct laryngoscopy. Laryngoscope 1996;106: 1280-6.

(3.) Ford CN. The technique of indirect laryngoscopy for botulinum toxin injection. Operative Techniques in Otolaryngology Head Neck Surgery 1993;4:191-5.

(4.) Sulica L, Blitzer A. Anesthesia for laryngeal surgery in the office. Laryngoscope 2000;110:1777-9.

(5.) Belafsky PC, Postma GN, Daniel E, Koufman JA. Transnasal esophagoscopy. Otolaryngol Head Neck Surg 2001;125:588-9.

(6.) Hogikyan ND. Transnasal endoscopic examination of the subglottis and trachea using topical anesthesia in the otolaryngology clinic. Laryngoscope 1999;109:1170-3.

(7.) Hogan Q. Local anesthetic toxicity: An update. Reg Anesth 1996;21(suppl):43-50.

(8.) Physician's Desk Reference. 58th ed. Montvale, N.J.: Thompson PDR, 2004.

(9.) Price D. Methemoglobinemia. Goldfrank's Toxicologic Emergencies. 5th ed. 1994:1169-80.

(10.) Wiles JR, Kelly J, Mostafa SM. Hypotension and bradycardia following superior laryngeal nerve block. Br J Anaesth 1989;63: 125-7.

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