The laryngeal mask airway

A new form of airway has recently been described, which is introduced blindly into the hypopharynx to form a seal around the larynx, so permitting spontaneous or positive pressure ventilation without penetration of the larynx or oesophagus. The further development of this new airway is described and the results of 18 months' clinical experience are presented. The airway was used successfully in 118 patients, 17 of whom received controlled ventilation of their lungs. It was used in place of the facemask in routine anaesthesia, and was of particular value in ophthalmic, dental and ear, nose and throat procedures and where difficulties with the airway were expected. The incidence of sore throat and other problems was low. Experience of more than 500 cases suggests that the laryngeal mask airway may have a valuable r?le to play in all types of inhalational anaesthesia, while its proven value in some cases of difficult intubation indicates that it may contribute significantly to the safety of general anaesthesia.     

Physiological dead space/tidal volume ratio during face mask, laryngeal mask, and cuffed oropharyngeal airway spontaneous ventilation

Objective: To compare the physiological dead space/tidal volume ratio and arterial to end-tidal carbon dioxide tension (ETCO₂) difference during spontaneous ventilation through a face mask, a laryngeal mask (LMA), or a cuffed oropharyngeal airway.

Design: Prospective, randomized, cross-over study.

Setting: Inpatient anesthesia at a university department of orthopedic surgery.

Patients: 20 ASA physical status I and II patients, without respiratory disease, who underwent ankle and foot surgery.

Interventions: After a peripheral nerve block was performed, propofol anesthesia was induced and then maintained with a continuous intravenous (IV) infusion (4 to 6 mg/kg/h). A face mask, a cuffed oropharyngeal airway, or an LMA were placed in each patient in a random sequence. After 15 minutes of spontaneous breathing through each of the airways, ventilatory variables, as well as arterial, end-tidal, and mixed expired CO₂ partial pressure, were measured, and physiological dead space/tidal volume ratio was calculated.

Measurements and Main Results: Expired minute volume and respiratory rate (RR) were lower with LMA (5.6 ± 1.2 L/min and 18 ± 3 breaths/min) and the cuffed oropharyngeal airway (5.7 ± 1 L/minand 18 ± 3 breaths/min) than the face mask (7.1 ± 0.9 L/min and 21 ± 3 breaths/min) (p = 0.0002 and p = 0.013, respectively). Physiological dead space/tidal volume ratio and arterial to end tidal CO₂ tension difference were similar with the cuffed oropharyngeal airway (3 ± 0.4 mmHg and 4.4 ± 1.4 mmHg) and LMA (3 ± 0.6 mmHg and 3.7 ± 1 mmHg) and lower than with the face mask (4 ± 0.5 mmHg and 6.7 ± 2 mmHg) (p = 0.0001 and p = 0.001, respectively).

Conclusion: Because of the increased dead space/tidal volume ratio, breathing through a face mask required higher RR and expired minute volume than either the cuffed oropharyngeal airway or LMA, which, in contrast, showed similar effects on the quality of ventilation in spontaneously breathing anesthetized patients.     

The intubating laryngeal mask. Clinical appraisal of ventilation and blind tracheal intubation in 110 patients

This study assesses the efficacy of the intubating laryngeal mask as a ventilation device and blind intubation guide. Following induction of anaesthesia with propofol, the device was successfully inserted at the first attempt in 110/110 (100%) patients. Placement took less than 10 s in all patients. Size selection was based on nose-chin distance. Adequate ventilation was achieved in 104/110 (95%) patients. Blind tracheal intubation using an 8-mm internal diameter straight silicone cuffed tracheal tube was attempted 3 min after the administration of vecuronium. Passage of a lighted stylet through the intubating laryngeal mask was used to determine the position of the intubating laryngeal mask cuff before blind intubation. If resistance was felt during intubation, a sequence of adjusting manoeuvres was used, based on the depth at which resistance occurred. Tracheal intubation was possible in 104/104 (100%) patients. In 42 (40%) patients, no resistance was encountered and the trachea was intubated at the first attempt. Sixty-two (60%) patients required one adjusting manoeuvre. The mean (range) time taken to successful intubation, i.e. the time from disconnection of the intubating laryngeal mask from the breathing system to successful tracheal intubation, was 79 (12-315) s. Six patients with potential or known intubation problems were included in the study. The tracheas of all six patients were successfully intubated. We conclude that the intubating laryngeal mask is an effective ventilation device and intubation guide with potential for use in patients who may present difficulty in tracheal intubation.     

Gas leakage and the laryngeal mask airway: A comparison with the tracheal tube and facemask during spontaneous ventilation using a circle breathing system

The ability of the laryngeal mask airway, tracheal tube and facemask to provide a leak free seal in a clinical setting was assessed by measuring the minimal fresh gas flows needed in a closed circle system during spontaneous ventilation on 60 subjects. The fresh gas flow was reduced until no spillage occurred from the pop-off valve. This fresh gas flow was taken to represent the sum of gas uptake by the subject and gas leakage from the circuit. The median fresh gas flow after 20 minutes was 350 ml. min⁻¹ in the laryngeal mask airway group, 350 ml. min⁻¹ in the tracheal tube group and 450 ml. min⁻¹ in the facemask group. The fresh gas flow required for the facemask group was significantly higher than that for the laryngeal mask airway or tracheal tube groups (p < 0.01). There was no significant difference between the fresh gas flows required for the tracheal tube and laryngeal mask airway groups. We conclude that the laryngeal mask airway provides as good a gas tight seal as a tracheal tube in this context and would be of benefit in reducing anaesthetic gas pollution.     

The laryngeal mask airway

A prototype size 3 laryngeal mask was used in 100 patients by 18 anaesthetists with no previous experience of its use. A clear and unobstructed airway was obtained in 98% of patients, without requiring support of the jaw, thus leaving the anaesthetists' hands entirely free. The patency of the airway did not deteriorate during the course of the anaesthetic. In 10 patients there was obstruction of the airway at the first attempt to place it without the introducer and this obstruction appeared to be as a result of downfolding of the epiglottis. Subsequent attempts at passage were successful in all 10 patients. The seal between the mask and the larynx was adequate for artificial ventilation of the patients, but the mean leak pressure was 1.7 kPa.     

The laryngeal mask airway

The laryngeal mask airway is an important addition to the anaesthetist's armamentarium, but its use is not without the possibility for misfortune. We encountered an unusual and potentially serious complication. A patient's epiglottis became trapped between the pliable grates in the mask portion of the laryngeal mask and partially obstructed his airway. Should this problem occur and remain unnoticed, in addition to the problem of airway obstruction during the anaesthetic, the oedematous epiglottis could be severely injured upon removal of the laryngeal mask. This, in turn, could result in airway obstruction requiring emergency treatment.     

The laryngeal mask airway in children

The laryngeal mask airway was used in 200 children during a variety of surgical procedures. Some problem with the use of the device was encountered in 47 cases (23%), but in only five cases (2.5%) were the problems serious enough to warrant abandonment of its use. A clear airway was ultimately achieved in 191 children. Downfolding of the epiglottis over the laryngeal inlet was identified in eight out of 24 patients where flexible laryngoscopy was performed, clinically all these had unobstructed airways. The mask was used in 16 children with known airway problems. It is concluded that the size 2 laryngeal mask airway can be successfully used within the weight range 6-30 kg.     

The laryngeal mask airway

Two cases of emergency prehospital airway control using the laryngeal mask are described. The patients were trapped following road traffic accidents and limited access prevented tracheal intubation. The laryngeal mask airway may be a useful alternative to tracheal intubation in some cases of prehospital trauma care.     

Damage to the laryngeal mask by residual fluid in the cuff

It has been suggested that, in some situations, the cuff of the laryngeal mask should be filled with fluid. We speculated that this practice might damage the device during sterilisation in an autoclave. We studied whether injection of a small volume of water into the cuff of the laryngeal mask and subsequent sterilisation affected the integrity of the cuff. First, a pressure–volume relationship for each of 20 new masks was obtained by inflating the cuff with increasing volumes of air (5–45 ml). The masks were then randomly allocated into four groups (W₀, W_0.25, W_0.5 or W_1.0), 0, 0.25, 0.5 or 1.0 ml of water was injected into the cuff and the mask was then sterilised in an autoclave. After sterilisation, the shape of the cuff was examined and pressure–volume relationships were obtained again. The baseline intracuff pressures were similar in the four groups. After sterilisation, the pressure was significantly lower in groups W_0.25, W_0.5 and W_1.0 than in group W₀ (p < 0.05). Two masks in group W_1.0 lost their integrity, resulting in herniation of and rupture of the cuff. We conclude that the cuff of the laryngeal mask should not be inflated with fluid unless the device is discarded afterwards.     

The use of the laryngeal mask airway by nurses during cardiopulmonary resuscitation

A multicentre study was undertaken to assess the potential value of the laryngeal mask airway when inserted by ward nurses during resuscitation as a method of airway management, prior to the arrival of the Advanced Life Support Team with tracheal intubation capability. The nurses underwent a training programme agreed by all the participating hospitals and followed an identical protocol and data recording system. One hundred and thirty nurses were trained and 164 cases of cardiac arrest were studied. The laryngeal mask airway was inserted at the first attempt in 71% and at the second attempt in 26% of cases. Satisfactory chest expansion occurred in 86% of cases. The mean interval between cardiac arrest and laryngeal mask airway insertion was 2.4 min. Regurgitation of gastric contents occurred before airway insertion in 20 cases (12%), during the insertion in three cases (2%), but there was clinical evidence of pulmonary aspiration in only one patient, who survived to leave hospital. We conclude that the laryngeal mask airway offers advantages over other methods of airway and ventilation management, such as the bag-valve-mask or mouth-to-mouth methods that are currently used by ward nurses in resuscitating patients with cardiac arrest. In this study, the laryngeal mask airway was not being compared with the tracheal tube.