Topical airway anaesthesia for awake fibreoptic intubation

Editor, Securing the airway during general anaesthesia in patients with difficult airways poses a risk to the patient and presents challenges for the anaesthesiologist [1–3]. Therefore, awake fibreoptic intubation is the safest approach to airway management. It is usually carried out under topical anaesthesia or light sedation. Upper airway anaesthesia should be administered to a level sufficient to suppress the gag, swallow and cough reflexes, and to avoid pain [1–3]. The more cooperative the patient is, the easier the procedure [4]. There are multiple ways of administering anaesthesia for fibreoptic intubation via the oral or nasal route. We describe the use of an ultrasonic nebulizer (Multisonic Schill GmbH, Probstzella, Germany) that has been designed to deliver liquid medication in the form of droplets with an average diameter of just 3.5 μm to the airways. Ultrasonic nebulizers are often used in the treatment of pulmonary hypertension [5]. They can be easily integrated into the breathing circuit using an adapter. This arrangement provides the delivery of a sufficient dose of local anaesthetic only during inspiration as well as an optimum preoxygenation. Because of the particularly fine mist of vaporized anaesthetic, a remarkably lower dose of lidocaine is needed. Two case examples are described in the following. The first case involves an awake fibreoptic intubation in a setting documented by experienced anaesthesiologists as being a ‘cannot ventilate – cannot intubate’ situation during previous general anaesthesia. A patient undergoing elective aortic valve replacement and aortocoronary bypass surgery for severe aortic stenosis and three-vessel coronary artery disease required tracheal intubation. The patient had concomitant chronic obstructive pulmonary disease and used nasal continuous positive airway pressure every night to treat obstructive sleep apnoea. After a detailed explanation of the procedure on the day preceding surgery, the patient was premedicated with 7.5 mg of oral midazolam and was administered 100 mg of lidocaine (2%) via the ultrasonic nebulizer described above. Awake oral fibreoptic intubation was successfully performed. The cooperative patient did not exhibit signs of stress and, consequently, did not require additional analgosedation. General anaesthesia was induced subsequently by using intravenous etomidate (0.3 mg kg−1), fentanyl (0.01 mg kg−1) and pancuronium (0.1 mg kg−1). The second case describes an awake fibreoptic intubation in emergency transnasal surgery for optic nerve decompression because the patient manifested acute amaurosis that was induced by a known tumour. The patient had undergone several previous surgeries for carcinoma of the base of the tongue (mouth floor resection and resection of parts of the tongue, flap for closure of the defect, and neck dissection). Evaluation of anamnestic data of previous operative interventions revealed that the only possibility was to fibreoptically intubate this patient. Painful experience with previous awake fibreoptic intubations resulted in the patient exhibiting signs of anxiety, accompanied by a stress reaction. After a detailed explanation of the procedure, the patient was premedicated with 2 mg of intravenous midazolam. Although being treated with continuous infusion of remifentanil 0.1 μg kg−1 body weight min−1, the patient received a 10 min treatment of 100 mg lidocaine (2%) that was aerosolized by the ultrasonic nebulizer. Awake fibreoptic orotracheal intubation was performed without any problems. The patient was cooperative during the entire process. General anaesthesia was then induced with propofol (2 mg kg−1), remifentanil (0.3 μg kg−1 body weight min−1) and atracurium (0.5 mg kg−1). Preparations for nasotracheal intubations should include instilling a vasoconstrictor into the nasal cavities in order to reduce mucosal oedema [1]. Local anaesthesia can be applied to the upper airway in multiple ways. Glossopharyngeal and superior laryngeal nerve blocks are often difficult to perform and may involve damage to nerves. If the agents are administered topically in the form of gargles, sprays, lozenges, creams or impregnated swabs, high doses [6,7] up to the maximum dose [8] of topical anaesthetics may be necessary. Neither of these two approaches results in an anaesthesized trachea distal beyond the glottis. Topical administration of anaesthetic agents makes it difficult to say whether or not the larynx was adequately anaesthesized. Laryngeal anaesthesia may be provided by translaryngeal injection, via the working channel of the flexible bronchoscope or via a (e.g. epidural) catheter inserted [9] at end-expiration and under the anaesthesiologist's direct vision. All these methods are likely to induce cough in the patient. Nebulizing the topically applied inhaled anaesthetic is a possible solution to this problem. Customary compressed air-driven jet nebulizers atomize only highly concentrated anaesthetics (e.g. lidocaine 4–10%), so that the maximum dose of local anaesthetic (lidocaine 9 mg kg−1 body weight) can be exceeded within a short period of time [6]. Woodall et al.[10] recently published the experiences of anaesthesiologists undergoing awake fibreoptic intubation, one-third of whom found the side effects produced by lidocaine to be the most common complication. In the two cases described above, the use of an ultrasonic nebulizer effected sufficient airway anaesthesia with considerably lower doses of lidocaine. Upper airway anaesthesia and suppression of gag and cough reflexes was obtained by using only 100 mg of vaporized lidocaine. Thanks to cooperative patients, that is, they stuck out their tongues and raised the floor of their mouths, the pharyngeal lumen was fully opened. This manoeuvre essentially improved the view during endoscopy and made it so much easier to perform intubation. We believe that this procedure, involving the use of an ultrasonic nebulizer, offers important advantages compared with the other procedures mentioned as follows. Considerably smaller doses of local anaesthetics are required [2], and adequate preoxygenation and anaesthesia of the airway are achieved rapidly, easily and simultaneously. The ultrasonic nebulizer can be easily integrated into any system, it is easy to clean and sterilize and it reduces the number of devices that are needed in such clinical situations. Ultrasonic nebulizers are tailored to meet the patients' needs and enable them to cooperate with the anaesthesiologist. These findings may influence clinical practice in the management of the difficult airway during anaesthesia.