The purpose of this article is to provide otolaryngologists with specific instructions on how to adequately perform topical anesthesia for the most commonly performed laryngeal office-based procedures. In this article, patient selection, lidocaine dosing and safety, and patient monitoring are reviewed.
Key points
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Most procedures for laryngotracheoesophageal pathologies can be addressed solely through the nose.
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Flexible endoscopy, whether as transnasal esophagoscopy (TNE) or to monitor transoral injection augmentation, is a staple of office-based procedures.
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Typically, diagnostic tracheobronchoscopy only requires 2 mL to 3 mL of topical anesthesia.
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Amide and ester anesthetics reversibly block the sodium channels of the lipid membrane in nerve membranes; these anesthetics are more effective at penetrating unmyelinated nerve fibers that carry autonomic, pain, and temperature impulses.
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Judicious application of topical anesthesia has high safety profile and usually requires minimal patient monitoring.
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The toxicity threshold for anesthesia may be lower for those with systemic medical problems. When in doubt, patient safety may dictate a visit to the operative suite.
Background
In the past 20 years, office-based procedures, fueled by advancements in endoscopy technology and pushed by the trend toward minimally invasive procedures, have expanded the armamentarium of many otolaryngologists. These procedures encompass diagnosis and intervention of the larynx, tracheobronchial tree, and esophagus. Technology, skill, and experience of the physician can determine success or failure of an office-based procedure; yet, none of the former can overcome an inadequately anesthetized patient who is uncomfortable and anxious. This article discusses the techniques and pharmacology of anesthesia for office-based procedures.
Background
In the past 20 years, office-based procedures, fueled by advancements in endoscopy technology and pushed by the trend toward minimally invasive procedures, have expanded the armamentarium of many otolaryngologists. These procedures encompass diagnosis and intervention of the larynx, tracheobronchial tree, and esophagus. Technology, skill, and experience of the physician can determine success or failure of an office-based procedure; yet, none of the former can overcome an inadequately anesthetized patient who is uncomfortable and anxious. This article discusses the techniques and pharmacology of anesthesia for office-based procedures.
Approaches
The choice of approaches toward achieving adequate anesthesia for office-based procedures is dictated by the experience of the surgeon and the assistant, the selection of equipment, the target location of treatment, the duration of treatment, and patient anatomy/tolerance.
Transnasal Approach
Most procedures for laryngotracheoesophageal pathologies can be addressed solely through the nose, because most otolaryngologists are well trained in flexible laryngoscopy. Before the start of the procedure, both nasal cavities are sprayed with topical 2% oxymetazoline followed by 2% tetracaine. Based on the experience of the senior author (C.B.S.), the most effective way to apply nasal anesthesia is by providing multiple short pulses of spray directed along the floor of the nose. A working channel flexible laryngoscope is then passed transnasally to provide an indirect view of the base of the tongue and laryngopharyngeal complex.
Through the working channel, approximately 1 mL of 4% lidocaine is applied to the base of the tongue, and the remaining 2 mL to 4 mL are applied as 0.5 mL to 1 mL individual aliquots to the laryngeal surface of the epiglottis, supraglottis, and true vocal folds during phonation (holding a long E ), which produces the “laryngeal gargle,” a term coined by Hogikyan. For anesthesia of the tracheobronchial tree, at the end of the phonatory gesture, the patient is instructed to breathe deeply to inspire the lidocaine while being informed that first few breaths will trigger a strong cough reflex. This deep inspiration is usually not needed for procedures isolated to the larynx. The endpoint of adequate anesthesia is marked by the following:
- 1.
Absence of cough reflex during lidocaine aspiration
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Absence of gag reflex
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Anesthesia of the larynx during palpation of the epiglottis, base of the tongue, posterior glottis, and bilateral true vocal folds
This approach, if adequately performed, allows procedures of the larynx and tracheobronchial tree. Typically, diagnostic tracheobronchoscopy requires only 2 mL to 3 mL of topical anesthesia.
Transoral Approach
Delivering lidocaine through the mouth is an alternative to the transnasal approach, as initially described by Hogikyan. This approach still requires the video guidance of a flexible laryngoscope. Indications for this approach include surgeon/patient preference or narrow nasal passage that precludes passage of a larger working channel endoscope. The administration of topical anesthesia transorally should be performed in the following sequence:
- 1.
Spray the base of tongue, palate, and posterior pharynx with topical cetacaine spray (13% benzocaine/2% butamben/2% tetracaine).
- 2.
Apply nasal anesthesia (as described previously) to allow insertion of the flexible laryngoscope.
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Drip 3 mL to 5 mL of 4% lidocaine onto the base of tongue and larynx using an Abraham cannula or a laryngotracheal atomizer spray device (MAD 600, Wolfe Tory Medical, Salt Lake City, Utah) under endoscope guidance.
Patient selection
Office-based procedures are well tolerated by most patients. Nevertheless, the following patient characteristics should be considered before embarking on the procedure.
Nasal Patency
Flexible endoscopy, whether as TNE or to monitor transoral injection augmentation, is a staple of office-based procedures. The distal-chip flexible laryngoscope (ENF-VQ, Olympus Surgical, Orangeburg, New York), used in the authors’ practice, has an outer diameter of 3.6 mm. The working channel endoscope (ENF-VT2, Olympus, Center Valley, Pennsylvania) has an outer diameter of 4.9 mm. The patient must have a unilateral nasal passage large enough to accommodate the largest endoscope needed for the procedure without significant discomfort.
Oral Passage
For transoral procedures, an interincisor distance of 2 cm or greater is recommended to allow instrumentation.
Gag Reflex
Gag reflex is triggered by the afferent branch of cranial nerve IX. This response varies greatly between individuals. A hyperresponsive gag may be present even with adequate administered topical anesthesia thus rendering flexible endoscopy and/or transoral instrumentation impossible.
Patient Cooperation/Tolerance
Most office-based procedures take 5 to 15 minutes to complete. Procedures, especially those that address the true vocal folds, require patients to remain still and upright. Patients with significant head tremor, vocal fold movement, or torticollis are challenging to treat.
Topical anesthesia safety
Topical or local anesthetics are classified into 2 groups:
- 1.
Amides
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Esters
These agents consist of an aromatic and an amine group separated by an intermediate group. The class that has an ester link between the intermediate group and the aromatic portion is called esters, and the amides have an amide link.
Examples of esters include
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Tetracaine
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Benzocaine
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Procaine
Examples of amides are
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Lidocaine
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Mepivacaine
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Prilocaine
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Bupivacaine
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Etidocaine
A mnemonic device is that the names of amides contain 2 i ‘s compared with only 1 i seen in esters.
When applied topically or locally, amide and ester anesthetics reversibly block the sodium channels of the lipid membrane in nerve membranes. These anesthetics are more effective at penetrating unmyelinated nerve fibers that carry autonomic, pain, and temperature impulses. The main considerations in the clinical use of these agents are potency, duration of anesthesia, the speed of onset, and maximum dose. Potency is determined by the lipid solubility of the agent. Less potent local anesthetics must be given in higher concentration and larger doses. The ability of the anesthetic to bind to proteins in the sodium channel predicts its duration of anesthesia. The onset of action relates to how fast the agent can diffuse through tissues to the nerve. A general reference maximum dose normally exists for various anesthetics; however, actual toxic dose depends on individual patients and their ability to clear the drug.
Lidocaine
Lidocaine has a low to intermediate potency, 45 to 60 minutes duration of action, and onset of sufficient anesthesia within 90 seconds of topical administration. Lidocaine solutions can be found in 1%, 2%, and 4% solutions. The dosage can be calculated from the percentage of lidocaine. For example, 1% lidocaine contains 10 mg/mL, and, for the purpose of office-based procedures, 4% lidocaine translates into 40 mg/mL of lidocaine. Five milliliters of 4% lidocaine equals 200 mg. Commonly quoted maximum dose of 3 mg/kg to 5 mg/kg (pure lidocaine without epinephrine) can lead to systemic toxicity. A 70-kg patient can receive approximately 300 mg of lidocaine. The authors recommend weighing all patients before performing any office-based procedure.
Topical application of lidocaine
Topical application of lidocaine for the purpose of office-based procedures rarely exceeds the toxic dose. Lidocaine-associated toxicity has not been cited in the otolaryngologic literature for the purpose of office-based laryngotracheoesophageal procedures. Postma and colleagues reported 700 consecutive cases of TNE performed in the office using 4% lidocaine without a single case of lidocaine related adverse events (see the article by Bush and Postma elsewhere in this issue). Verma and colleagues published 68 cases of TNEs with 4% topical lidocaine without adverse effects. From the senior author’s experience of more than 200 cases of KTP laser treatment of benign vocal fold lesions (Wang, Fuller and Simpson, personal communication, 2011), not a single procedure was aborted due to lidocaine-related adverse effects. The importance of lidocaine’s pharmacology and safety profile, however, cannot be overlooked to prevent potential lidocaine toxicity.
Lidocaine toxicity
The half-life of lidocaine is 90 minutes regardless of mode of administration. Systemic reactions to lidocaine involve the central nervous system (CNS) and the cardiovascular system, with the CNS more susceptible. The typical neurologic symptoms of lidocaine toxicity include lightheadedness and dizziness followed by visual and auditory disturbances, such as difficulty focusing and tinnitus. Signs of CNS toxicity are usually excitatory, which may include shivering, muscular twitching, and tremors. Unrecognized and untreated overdose may lead to generalized seizures, followed by coma and respiratory depression. The depressant effects predominate at higher doses. Cardiovascular toxicity of lidocaine derives from the inhibition of sodium channels in the nerve membrane. Lidocaine exerts a dose-dependent negative inotropic effect on cardiac muscle, reducing contractility and interfering with conduction. Lidocaine toxicity can be potentiated by renal impairment, liver disease, and cardiac conditions.
If there is evidence of central nervous system involvement or cardiovascular instability, local anesthetics application and procedure should be discontinued. Pulse oximetry and hemodynamic monitoring should be initiated. Early oxygen supplementation could prevent hypoxia and acidosis and halt progression toward seizure and cardiovascular collapse. When significant overdose is suspected, patients need to be transferred to a facility with anesthesia and ICU support. The detailed management of local anesthetic toxicity is outside the scope of this article. The authors refer to the guidelines published by the American Society of Regional Anesthesia.
Lidocaine allergy
True topical lidocaine allergy during endoscopy has not been reported. There have been reports of lidocaine causing both type I and type IV allergic reactions, however, during dental and cutaneous procedures.
Methemoglobinemia from lidocaine
Methemoglobinemia is a rare complication caused by the oxidation of hemoglobin from the ferrous state (Fe 2+ ) to the ferric state (Fe 3+ ). In the ferric state, hemoglobin cannot bind oxygen, thus leading to desaturations. Methemoglobinemia induced by lidocaine has been reported in the bronchoscopy literature when combined with benzocaine, a more powerful oxidizing agent. Methemoglobin is darker than unoxygenated hemoglobin and can produce chocolate cyanosis, a violet or brown discoloration on the lips, ears, and mucous membranes. Systemic symptoms of methemoglobinemia may vary from anxiety to headaches, fatigue, coma, and even death. Methemoglobin levels less than 30% usually resolve spontaneously over 15 to 20 hours when the offending agent is removed and oxygen is administered. For severe cases, methylene blue can be administered at a dose of 1 mg/kg to 2 mg/kg intravenously slowly over 3 to 10 minutes.
Tetracaine
Tetracaine is a highly potent local anesthetic with duration of anesthesia between 60 to 120 minutes when applied topically. According to anesthesiology literature, tetracaine has a slow onset and may take up to 10 minutes to achieve adequate anesthesia ; however, based on the authors’ experience, it seems to establish the anesthesia of the nasal passage faster than lidocaine. Furthermore, as topical nasal anesthesia, tetracaine has demonstrated superiority to cocaine and lidocaine both in terms of duration of action and pain control. Bourolias and colleagues showed that 2% tetracaine solution resulted in significantly less nasal discomfort when compared with 10% lidocaine with transnasal laryngoscopy. Similarly, 2% tetracaine plus adrenaline demonstrated improved intraoperative pain controlled compared with 4% cocaine for septoplasty.
Tetracaine toxicity
Significant tetracaine associated toxicity has not been reported when applied topically through the nose. The half-life and systemic absorption of nasal tetracaine spray have not been clearly defined in the literature. Earlier reports of fatalities with local mucosal application of tetracaine came at doses greater than 100 mg. The authors do not routinely measure the dose of 2% tetracaine nasal spray applied during office-based procedures; however, it is recommended to use less than 1 mL of 2% tetracaine for nasal anesthesia. Typically, only 0.1 mL to 0.2 mL is needed when delivered through an atomizer. The authors do not recommend dripping tetracaine for office-based procedures because this route of application can significantly escalate the dose delivered.
Combining tetracaine and lidocaine
Tetracaine is of ester class of local anesthetics, unlike lidocaine, which is an amide. Animal study has shown that when combining amide and ester anesthetics, their effects are neither synergistic nor antagonistic. This relationship may not hold true in humans, however, and clinicians should be cautioned to not use maximum doses of 2 different local anesthetics, regardless of their class, in combination, assuming that their toxicities are independent.
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