Airway topicalisation using atomisation of lidocaine

Abstract

We read the recent article of Woodruff et al. [1] with interest. A major advantage of the atomisation with lidocaine used in this study is the rapidity with which the airway can be anaesthetised, but this is achieved at the expense of administration of a large dose over a short time (about 5 min). We have concerns over the safety of this topicalisation method in general clinical practice, particularly when the drug is rapidly administered to non-obese patients. The British Thoracic Society has recommended a maximum lidocaine dosage of 8.2 mg.kg−1 for airway topical anaesthesia during bronchoscopy [2], but these drugs are administered in fractional doses at different sites in the airway over a prolonged time period. Compared with a large dose used in a shorter time, fractional doses sprayed over a longer period result in a lower plasma drug level [3]. Moreover, we do not agree that a large dose of lidocaine is safe in routine clinical practice for two reasons. First, lidocaine pharmacokinetics are complex, being affected by many factors, so the plasma lidocaine concentration achieved in a particular patient is often unpredictable. Even with recommended doses, patients may still sometimes achieve an unexpectedly high plasma concentration [4]. After large doses of lidocaine (7.1–14.8 mg.kg−1) administered by a spray-as-you-go technique, 36–92% of subjects report symptoms attributable to lidocaine toxicity [5, 6]. In addition, a healthy volunteer has died from lidocaine toxicity after fibreoptic bronchoscopy [7]. Second, lidocaine toxicity can occur even when the plasma lidocaine levels are in a ‘safe’ range [3, 8]. The authors suggest that airway topicalisation using nebulisation requires a long preparation time and may interfere with rapid turnover of patients. However, this technique can be safely performed in the holding area. We would also like to call the authors’ attention to the two papers in which low doses of nebulised lidocaine (100 or 160 mg) achieved adequate airway anaesthesia in most patients [9, 10]. We appreciate the reference to our recent article [3], but believe that Woodruff et al. have misrepresented our time (> 20 min) for airway topicalisation. As the main aim of our study was to compare the safety and efficacy of 2% and 4% lidocaine to produce airway topical anaesthesia with a spray-as-you-go technique, the repeated lidocaine sprays in the airway were performed at a 3–5 min interval to provide adequate penetration of local anaesthetic into the mucosa for maximal effect, and the whole airway topicalisation protocol required 19.2–28.2 min. The authors think that this prolonged time for airway topicalisation may sometimes be unacceptable. However, we feel that, as with other local anaesthetic methods, ‘tincture of time’ is a useful supplement to the application of airway topical anaesthesia. Inadequate airway topical anaesthesia due to the slow onset of the maximal effect can often result in larger doses' being given or repeated drug delivery in a short time, leading to overdose.