Preparation of the airway for awake intubation.

Sir,

The article by Prof. Ramkumar, “Preparation of the patient and the airway for awake intubation” is an important contribution.[1] The article comprehensively discusses various practical and clinically relevant aspects of both patient and airway preparation. The importance of psychological preparation of the patient, which is often times neglected, is well highlighted. Four additional points deserve commentary.

Nebulization of lignocaine 2-4% has been successfully used for topical anaesthesia of the airway in fibreoptic bronchoscopy and fibreoptic intubation.[2] This technique is simple, non-invasive and avoids the unpleasantness and severe coughing associated with translaryngeal injection. It is especially suitable in situations where the translaryngeal injection may be impossible or difficult, such as in patients with a huge neck mass, deep neck infection or superior venacaval obstruction.

The author correctly emphasizes the importance of keeping a “close track of the total amount of local anaesthetic drug used to prevent inadvertent drug toxicity”. In this regard, the British Thoracic Society recommended that the total dose of lignocaine applied during bronchoscopy should be limited to 8.2 mg/ kg.[3] This is because the drug is administered in fractional doses at different sites in the airway over a prolonged time period. Caution should be exercised in the elderly and in those with liver or cardiac disease.[4] The lean body weight should be considered in obese subjects. Lignocaine is rapidly absorbed from the upper airway, tracheobronchial tree and alveoli into the bloodstream, with peak blood concentrations generally reached at 20-40 min after application. Lignocaine toxicity correlates directly with its concentration in the blood. The risk of serious toxic effects increases when blood concentrations exceed 5 mg/L, with seizures and hallucinations occurring at concentrations of 8-12 mg/L and cardio-respiratory arrest at 20-25 mg/L.[5]

The author suggests that the translaryngeal injection be made at the end of a deep inspiration. While this practice is followed by many, an alternate technique involves injection of lignocaine at the end of expiration. The patient is instructed to take a deep breath and then exhale. After confirmation of an intralaryngeal position by aspiration of air, lignocaine is injected at end-expiration. A deep inhalation and cough immediately following injection distributes the anaesthetic throughout the trachea.[6]

Lignocaine 2% viscous should be “gargled” for as long as possible in order to anaesthetize the posterior pharyngeal wall and base of the tongue besides being “swished around in the mouth”.