A reply

Xue and colleagues raise a number of important issues regarding our recent publication that compared atomised 1% with 2% lidocaine for topical airway anaesthesia in the morbidly obese [1]. In that study we demonstrated that 40 ml of 2% atomised lidocaine, using high-flow oxygen as the carrier gas, produced superior airway anaesthesia for awake fibreoptic intubation compared to 1% lidocaine. Mean (SD) peak plasma lidocaine concentration with 2% atomised lidocaine was 3.8 (0.5) μg.ml−1 following the end of atomisation and no signs of clinical toxicity were observed. These findings were consistent with the results of our previous study [2] which demonstrated that airway anaesthesia for awake oral fibreoptic intubation achieved by atomised 2% lidocaine in the morbidly obese is an efficacious and safe technique (peak plasma lidocaine concentration 2.8 (0.8) μg.ml−1). We emphasised in our reports that our observations apply only to the morbidly obese population. Furthermore, we have cautioned that in certain subjects, including patients with decreased lean body mass, hepatic or renal disease, airway topicalisation may result in toxic plasma levels of local anaesthetic drug. We have also highlighted that hypercarbia can decrease the seizure threshold for local anaesthetic plasma concentration and so particular caution should be exercised when embarking on airway topicalisation in patients with respiratory compromise. With these caveats in mind, we would point out that we have successfully used atomised lidocaine to produce topical airway anaesthesia for awake fibreoptic intubation in hundreds of cases and have invariably found this to be effective and safe. We respectfully submit that we have correctly interpreted Xue et al.’s [3] time for airway topicalisation, as gleaned from Table 2 of their article clearly indicating a ‘total time for airway sprays’ of 24.3 (3.8) min (1% lidocaine) and 22.8 (3.5) min (2% lidocaine). We continue to believe that one of the advantages of the atomised lidocaine technique is the rapidity at which the airway can be anaesthetised (< 5 min [1, 2]). This may not only facilitate a rapid yet safe turnover of patients in a high-volume bariatric surgery program, but may be crucial in critical situations demanding prompt airway management [2]. Airway anaesthesia that permits awake fibreoptic intubation can indeed be established with a lower (1%) concentration of atomised lidocaine [1], but this is associated with increased patient response to airway manipulation. As our previous studies were done in moderately sedated patients and because there is an inverse relationship between the level of sedation and the required depth of airway insensibility, topicalisation with lower concentrations of lidocaine may be acceptable, particularly if an increased level of sedation is targeted. While we are convinced of the merits of the lidocaine atomisation technique, as articulated above, it is naïve to think that any one method of airway anaesthesia is ideally suited to every clinical situation. As such, debate on the superiority of any one technique (e.g. atomisation vs ‘spray-as-you-go’) is of limited value. Rather, each technique must be evaluated on its strengths and weaknesses in the context of patient and procedure, as we have emphasised previously.

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