The laryngeal mask airway in anticipated difficult airways.

Abstract

T HE primary principle of airway management in anaesthesia is to establish and maintain a patent airway to permit effective ventilation. When necessary, airway management also includes provision of a mechanical barrier to pulmonary aspiration of foreign material. The ASA Difficult Airway algorithm I is predicated on a gold standard of a cuffed endotracheal tube to meet both considerations in every case. This elevates the risk of aspiration to equal priority with effective ventilation, even when no risk factors for regurgitation or aspiration are present. When faced with a d i f f icul t airway, t h e t i m e h o n o u r e d a p h o r i s m o f anaesthe t i s t s is, I f in doubt, intubate the patient awake. The correctly positioned laryngeal mask airway (LMA) can provide a clear airway in 99% of cases. 2 It protects the lungs from aspiration of foreign material from above its cuff, but not from gastric contents. Therefore, when the threat of aspiration of gastric contents is present, even with an easy airway, use of the LMA is not recommended. The incidence of clinically significant pulmonary aspiration of approximately 1 in 10,000 in healthy patients undergoing elective surgery is similar for the LMA 2 and tracheal intubation or face mask. 3 If the patient's aspiration risk is low and total lung compliance is near normal, a correctly positioned LMA that allows effective ventilation meets the criterion of a secure airway with minimal risk. Aaaaesthetic practitioners have developed a variety of oropharyngeal and nasopharyngeal airway devices during the past hundred years, a including the LMA which became commercially available in the United Kingdom in 1988. Formulation of the ASA Difficult Airway Algorithm began in 1991, but the LMA was not released in the USA until October of that year. This algorithm has had a profound influence on anaesthetists' attitudes and education in the management of the difficult airway. When the algorithm was published in 1993, American experience of the LMA was limited and it did not receive mention. Since then, as experience has accumulated, the LMA has been promoted from a hands-free substitute for a Guedel airway in short, minor procedures with spontaneous respiration to an alternative to tracheal intubation in selected prolonged, major procedures with positive pressure ventilation. 2 Few individuals achieve and maintain a full repertoire of strategies and skills with all airway devices. Cormack has pointed out that, because of the rarity of genuinely difficult airway cases, controlled trials are not easy to do and anecdotal evidence can be useful, s Faced with uncertainty, few anaesthetists set aside the collective wisdom of the ASA Difficult Airway algorithm. However, the algorithm implies that tracheal intubation is the preferred management of every airway. Benumof has now indicated five points in the ASA algorithm where the LMA may have a role, 6 the evidence being based on numerous case reports that attest to its successful use in patients in whom difficult intubation was known or anticipated. 7 Intubation is either a success or failure, and failure leads to alternative second choices of mask ventilation, surgical airway, regional anaesthesia or cancellation of surgery. 'Difficult airway' is an umbrella term which does not distinguish among situations as disparate as tmsatisfactory face mask fit, difficult direct laryngoscopy, and pathological or congenital distortion of the larynx or trachea. Widespread experience with the LMA has challenged the practice of routine intubation in elective, healthy patients with normal and difficult airways. In this issue of the Journal, Giraud e t al. s report a series of nine patients in whom they used the LMA as the initial airway device in elective patients with recognised predictors of difficult intubation, but no risk fac-