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Department of Anesthesiology, Seoul National University College of Medicine, Seoul, Korea
To the Editor:
We read with interest the recent article by Fagan et al. (1) of the effects of intracuff lidocaine on endotracheal tube (ETT)-induced emergence phenomena after general anesthesia. Unfortunately, after approximately 1.5 h of general anesthesia, intracuff lidocaine was reported to decrease coughing only 4–8 min postextubation of trachea as compared with air or saline (1).
When the coefficient of diffusion and the thickness are the same, diffusion across a membrane depends on concentration and time. Because of the possibility of lidocaine toxicity in the event of cuff damage, we cannot use higher concentration of lidocaine. Huang et al. (2) reported that alkalization of lidocaine can promote the in vitro diffusion across the endotracheal tube cuff many tens of times. The alkalization of lidocaine and the surgery of long duration would make the method more effective. Use of a heated breathing circuit may have some additive effect because warming of lidocaine solution can increase the diffusion across the cuff membrane (2).
Coughing during operation and emergence can produce a serious problem, especially for neurosurgical, ophthalmic, and vascular procedures. Especially if these patients have difficult airway or when it is necessary to keep the ETT intubated during recovery period, intracuff lidocaine with alkalization may be helpful. Tracheostomized patients, who have to keep the tube for a long time and whose discomfort seems to come mainly from the inflated cuff, can benefit from intracuff lidocaine (3). Alkalization of lidocaine can also apply to these patients.
Lidocaine is frequently used during anesthesia just before intubation (4) and in the presence of ETT (5) to suppress coughing, or as an antiarrhythmic agent. It is common that surgeons subcutaneously inject the lidocaine premixed with epinephrine during neuro- or craniofacial surgery. For patients with high peak inflation pressure, we have to inject a larger volume of lidocaine into the cuff because the minimum occlusive pressure increases linearly with peak inflation pressure (6). We should be cautious not to use more than the maximum allowable dose.
In addition, intracuff lidocaine does not increase the cuff volume during the maintenance of general anesthesia with nitrous oxide. It would be more effective for certain kind of surgery like neuro- or craniofacial surgery because this type of surgery usually takes long time, and the pilot balloon port cannot be accessible for the cuff pressure adjustment without interrupting the surgical procedure.
Dr. Fagan does not wish to respond.
References
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