In vitro diffusion of lidocaine across endotracheal tube cuffs

Purpose: Lidocaine diffuses across endotracheal tube cuffs, which may serve as a reservoir for local anesthetic to assist in the prevention of Err-ind uced cough while emerging from general anesthesia. However, the rate of dif fusion is slow. Two techniques, alkalization and warming, may increase the proportion of uncharged drug available for diffusion. The purpose of this s tudy is to determine the effectiveness of warming alkalization or warming w ith alkalization on diffusion. Methods: Four preparations of lidocaine 4% were studied. Group (Gr) L-lidoc aine (24 degrees C), GrWL-warmed lidocaine (38 degrees C), Gr AL - alkalize d lidocaine (24 degrees C), Gr WAL - warmed, alkalized lidocaine (38 degree s C). Twenty-four Mallinckrodt 8.0 ID (Mallinckrodt Critical Care Division of Mallinckrodt, Inc., Glens Fails, New York) endotracheal tube cuffs were filled with 6 mi of one of the four preparations. They were then placed in a 20 mi water bath at 38 degrees C and samples were drawn from the water ba th at intervals for up to 360 min. The lidocaine concentration in each samp le was determined by gas chromatography. Results: The highest lidocaine concentration was reached in Gr WAL (410.98 +/- 8.53 mu g.ml(-1)) after 300 min and then decreased to 376.18 +/- 4.59 m u g.ml(-1) after 360 min. In Gr AL the highest concentration (235.05 +/- 2. 99 mu g.ml(-1)) was reached after 360 min. Lidocaine concentrations in Gr L and WL after 360 min were 3.19 +/- 1.16 mu g.ml(-1) and 4.32 +/- 2.02 mu g .ml(-1) respectively. Conclusion: Alkalization with or without warming, but not warming alone, pr omotes lidocaine diffusion from endotracheal tube cuff.