The laryngeal mask airway in anaesthesia

Abstract

The most frequent serious adverse respiratory events associated with anaesthesia are inadequate ventilation, oesophageal intubation and difficult intubation. ~ A clear upper airway is essential for gas exchange oxygenation, removal of carbon dioxide, and uptake and elimination of inhaled anaesthetics. This is often achieved for short operative procedures with a face mask and oropharyngeal airway, pulling up on the chin and, if necessary, thrusting the jaw forwards. A clear airway may be difficult to achieve or maintain in some patients because, although the Guedel airway prevents the tongue from falling back against the posterior pharyngeal wall, recent research suggests that this is not the only problem. A reduction in tone occurs in all pharyngeal structures during general anaesthesia and obstruction may occur at several sites.2,3 Furthermore, face masks are of standard shape and an airtight seal may be impossible to achieve in edentulous or bearded patients and in those with abnormal facial contours. Face mask anaesthesia in these patients is unsatisfactory because it is difficult and tiring, it occupies both hands of the anaesthetist, and it cannot be depended upon to provide an airtight circuit for positive-pressure ventilation. Passage of a cuffed tracheal tube ensures an airtight circuit so that the patient's inspired gases are not diluted by room air during spontaneous respiration, contamination of the operating room air is minimized and positivepressure ventilation can be used when necessary. Although protection of the lungs from gastric contents is important, in some cases over-riding importance, the commonest reason for passage of a tracheal tube in healthy, elective patients is the effortless maintenance of a clear airway. The technique was pioneered before the First World War although, until the introduction of muscle relaxants, it was often time-consuming and difficult and was only practised by a few specialist anaesthetists. 4 Because of this, Leech designed the pharyngeal bulb gasway 5 in Regina in 1935 to provide a clear airway with an airtight seal for closed circuit cyclopropane anaesthesia