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Absorption of lidocaine during aspiration anesthesia of the airway.

Prakash, Udaya B. S. M.D.

INTERVENTIONAL PULMONOLOGY IN OTHER JOURNALS: Commentary on Selected Publications
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Mayo Medical Center and Mayo Medical School, Rochester, Minnesota, U.S.A.

Absorption of lidocaine during aspiration anesthesia of the airway.

J Clin Anesth 2001;13:440–6. Mainland P, Kong AS, Chung DC, Chan CH, Lai CK. Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong.

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This randomized, double-blind clinical study of 96 adult patients scheduled for diagnostic FFB was designed to determine the optimal solution to use when anesthetizing the airway by aspiration of lidocaine. The 96 patients were classified as American Society for Anesthesia physical status I, II, and III, and these patients were randomized to receive one of five solutions of lidocaine. Group A (n = 16): 1% lidocaine, 0.2 mL/kg−1 (2 mg/kg−1); group B (n = 16): 1.5% 0.2 mL/kg−1 (3 mg/kg−1); group C (n = 32): 2% 0.2 mL/kg−1 (4 mg/kg−1); group D (n = 16): 1% 0.3 mL/kg−1 (3 mg/kg−1); and group E (n = 16): 2% 0.3 mL/kg−1 (6 mg/kg−1). All patients received 1 mg/kg meperidine and 0.01 mg/kg atropine 40 to 60 minutes before FFB. The nasal cavity was then anesthetized with 1.0 mL 5% cocaine solution applied with cotton-tipped swab. The aspiration technique was as follows: With the patient lying supine, lidocaine solution was trickled onto the back of the tongue over a period of 2 to 4 minutes. FFB was performed after the airway was anesthetized with the aspiration technique, using the assigned lidocaine solution. The bronchoscope was manipulated in the trachea to test for anesthesia. Successful airway anesthesia was determined by tolerance to FFB without sustained coughing, and also by the number of lidocaine supplements, if any, that were given via the FFB. Arterial plasma concentrations of lidocaine were measured in 33 patients from groups C, D, and E. All solutions provided equally effective anesthesia of the airway. All patients tolerated FFB through the vocal cords, and 94 patients required no supplementary anesthesia, or only one dose of lidocaine, during FFB to the carina. The highest peak plasma concentrations of lidocaine were 5.02 μg/mL and 6.28 μg/mL. No patient had signs of toxicity. The authors conclude that the aspiration technique produced anesthesia of the airway to the carina, safely, suitable for awake intubation, in 94 of 95 patients. The authors recommend use of 1% lidocaine, 0.2 to 0.3 mL/kg−1, so that the volume used is 10 to 20 mL. The “aspiration” technique described here is simple enough that it should be tried as one method of providing topical anesthesia before FFB. Topical anesthetic techniques for bronchoscopy include direct external injection of lidocaine through cricothyroid membrane, gargling of lidocaine by the patient, aerosolization of lidocaine through an aerosol machine, “spray-through-the-FFB-as-you-go” technique, and trickling of lidocaine onto laryngeal structures under mirror laryngoscopic technique. Clearly, no one technique works well in all patients. Each bronchoscopist eventually identifies one or two techniques that work the best for her/him and stays with them. In an occasional patient, other techniques including general anesthesia may be indicated. The most important point to remember is that the total dose of lidocaine is kept below toxic levels because a direct correlation exists between clinical symptoms and the blood level of lidocaine: As the level increases to 8 to 12 mg/L, the probability of seizure increases. The extent of absorption and bioavailability after airway administration depends on tissue vascularity, sites and techniques of application, the patient's disease state, and, most important, and the dose per unit body weight. Therefore, the lidocaine dose should be titrated slowly and patients should be monitored for altered mental status.

© 2002 Lippincott Williams & Wilkins, Inc.