In vitro diffusion of lidocaine across endotracheal tube cuffs

Smooth emergence from general endotracheal anesthesia is frequently complicated by coughing induced by stimulation from an endotracheal tube. Lidocaine and other local anesthetics have been shown to anesthetize important rapidly adpating stretch receptors in the dog trachea. With the aim of providing a reservoir for continuous lidocaine release to adjacent tracheal tissue, we examined the ability of clinically used concentrations of lidocaine to diffuse across a commonly used endotracheal tube cuff. Cuffs were filled with either 2% or 4% lidocaine and placed in a 200 mL bath with samples drawn at time intervals up to 360 minutes. Samples were then analyzed for lidocaine concentration. Another set of endotracheal tube cuffs were prefilled for one or 2.5 hours with 2% or 4% lidocaine, emptied, and then refilled with 2% lidocaine. They were then bathed and sampled as above. Cuffs exposed to 4% lidocaine during the prefilling or the diffusion stages resulted in significantly higher concentrations of lidocaine in the baths throughout the time course of the experiment, although all groups demonstrated a rise in the concentration of lidocaine in the baths with time. The highest concentration obtained was 17.49 +/- 2.03 micrograms/mL after 360 minutes. We conclude lidocaine diffuses across endotracheal tube cuffs in a fashion that may enable the cuff to serve a potentially useful role as a reservoir for local anesthetic. This in turn appears to have the potential to smooth emergence from general endotracheal anesthesia in those patients in whom tracheal stimulation may be a complicating factor.