[Fiberoptic determination of the position of the laryngeal mask].

The laryngeal mask airway (LMA) provides a patent airway when placed 'blindly' into the hypopharynx. At the laryngeal side it is supposed to form a seal surrounding the laryngeal inlet with the epiglottis lying outside the mask aperture. This study is designed to assess the prelaryngeal position of the mask by the fibreoptic technique. METHODS. After approval by the local ethical committee and informed consent, 100 adult patients (ASA groups I and II) undergoing general anaesthesia for extracorporal stroke wave lithotripsy (ESWL, Lithotripter HM 3, Dornier) of the kidney were studied. Anaesthesia was induced with propofol (1.5-2.5 mg.kg-1) and fentanyl (1-1.5 micrograms.kg-1) and maintained with isoflurane and N2O (65% in O2) as clinically indicated. The LMA was left in situ until the patients opened their mouth on command. Monitoring consisted of an ECG (SMV 104-D, Dornier), a pulse oximeter (Nellcor 200, Draeger), and a non-invasive blood pressure monitor (BP 103 N, Hoyer). Clinical assessment of airway patency and fibreoptic laryngoscopy (BF Typ 10, Olympus)--immediately and 20 min following the insertion of the LMA--were performed by two observers. RESULTS. The insertion of the LMA was successful on the first attempt in 89 patients while 5% required two, 4% three and 2% four attempts. 'Blindly' inserted without neuromuscular blockade the LMA provided a clinically sufficient airway in all patients. A central position of the LMA was assessed in only 59% of the cases. In 4 patients the mask was riding on the vocal folds. Positioned at the posterior larynx the cuff produced a compression of the laryngeal orifice when insufflated. Oblique insertion of the LMA or oblique head position during insertion produced a misplacement of the LMA. In 5 cases the LMA followed lateral movements of the head without losing its central position. In 87% the epiglottis was within the lumen of the LMA. Secretions inside the mask lumen or at the anatomic structures were seen in 36%. During manual ventilation with high inspiratory pressure (> 25 cm H2O) the oesophagus opened in 10 cases. CONCLUSIONS. Previous studies have suggested that the LMA takes a 'perfect' position at the laryngeal side when a clinically patent airway is recognized. In contrast, our results demonstrated that a central position of the LMA is achieved in only 59% of the cases. Our results indicate that epiglottic downfolding or left/right side or anterior/posterior misplacement are common but generally provide a satisfactory patent airway. This is consistent with fibreoptic findings in children and radiological observations in adults. The LMA is an essential enrichment to conventional airway management. It provides a better seal than the face mask, especially in bearded or in old patients where the facial contours are often not suited to the mask. Ideal indications seem to be elective operations of intermediate duration (1-2 h). The LMA does not protect against aspiration. For patients who are at risk of regurgitation of gastric contents, use of the LMA is absolutely contraindicated. Relative contraindications are local pathology of the pharynx and situations with low pulmonary compliance and/or high airway resistance (massive obesity, asthma, etc.), especially during controlled ventilation. Further studies are necessary to establish definite indications for the application of the LMA.