Laryngeal mask airway
A laryngeal mask is composed of an airway tube that connects to an elliptical mask with a cuff which is inserted through the patient's mouth, down the windpipe, and once deployed forms an airtight seal on top the glottis (unlike tracheal tubes which pass through the glottis) allowing a secure airway to be managed by a health care provider.
They are most commonly used by anaesthetists to channel oxygen or anaesthesia gas to a patient's lungs during surgery and in the pre-hospital setting (for instance by paramedics and emergency medical technicians) for unconscious patients.
The laryngeal mask was invented by British anaesthesiologist/anaesthetist Archibald Brain in the early 1980s and in December 1987 the first commercial laryngeal mask was made available in the United Kingdom. The laryngeal mask is still widely used today worldwide and a variety of specialised laryngeal masks exist.
A laryngeal mask has an airway tube that connects to an elliptical mask with a cuff. The cuff can either be of the inflating type (achieved after insertion using a syringe of air), or self-sealing. Once inserted correctly (and the cuff inflated where relevant) the mask conforms to the anatomy with the bowl of the mask facing the space between the vocal cords. After correct insertion, the tip of the laryngeal mask sits in the throat against the muscular valve that is located at the upper portion of the esophagus.
Dr. Archie Brain began studying the anatomy and physiology of the upper airway in relation to existing airways. Dr. Brain concluded that current techniques for connecting artificial airways to the patient were not ideal, reasoning that if the respiratory tree is seen as a tube ending at the glottis and the objective is to connect this tube to an artificial airway, the most logical solution was to create a direct end-to-end junction. Existing airway devices clearly failed to form this junction; the face-mask sealed against the face, and the endotracheal tube penetrated too far so that the junction was created within the trachea, instead of at its beginning. Dr Brain wrote in his diary in May 1981, "Better, use a loop fitting into the anatomical loop of space surrounding the larynx, with a projection downwards into the oesophagus, which could be hollow, to drain regurgitant fluid."
Dr Brain made cadaveric plaster casts of the space around and behind the glottis, a space adapted to the acceptance of foreign bodies in the form of food, therefore likely to tolerate an inflated cuff. Dr Brain recognised that if the boat shaped space were to be filled by an expandable cuff, an end to end seal could be formed. Dr Brain experimented with the Goldman Dental nasal mask cuff, if the flanges were drawn together in the midline, they produced a remarkable approximation to the plaster casts. The final step to create the first prototype laryngeal mask was to incorporate a tube. Satisfied by the results of inserting the prototype laryngeal mask into cadavers, the prototype laryngeal mask was first used in the summer of 1981 in a 40-year-old male patient undergoing an elective inguinal hernia repair. To Dr Brain's delight, it was possible to ventilate the lungs, indicating not only that the device provided a clear airway, but that it also formed an effective seal with the glottic inlet.
The first study of a laryngeal mask in 23 patients was conducted at London Hospital in 1982. Insertion and ventilation using the laryngeal mask in 16 anaesthetised, paralysed female patients was successful, achieving a seal greater than 20 cm H2O in all patients. Emergence from anaesthesia was also noted to be uneventful and only 3 patients complained of a sore throat, a marked contrast to endotracheal tube anaesthesia. Following the success of the initial study, Dr Brain successfully inserted and ventilated 6 anaesthetised, non-paralysed patients. Finding no difference between the first and second group of patients, Dr Brain realised that muscle relaxtion was not required for insertion. Finally, Dr Brain used the device in a dental extraction patient, he realised that because the space in and around the glottis was filled by the mask, the need for packing was much reduced and more impressively the larynx was completely protected from surgical debris. Brain realised the exciting possibility that the laryngeal mask could be applied to head and neck surgery and also observed that "In two patients the anatomy was such as to suggest that endotracheal intubation might have presented at least moderate difficulty. Neither presented difficulty with regard to insertion of the laryngeal mask ". By 1985, experience with the laryngeal mask prototype had reached 4000 cases. Dr Brain published a case series in Anaesthesia in 1985 describing the management of 3 difficult airway patients, illustrating the use of the laryngeal mask for airway rescue. Dr Brain with 5 co-authors published a second paper in anaesthesia describing the use of the laryngeal mask in over 500 patients, adding considerable credence to the laryngeal mask concept. However the limitation of the prototypes remained, a new material was urgently needed.
Search for new material
Following the realisation that a new material was needed, Brain looked at a number of options; polyvinyl chloride was too rigid and synthetic foam did not lend itself to re-use. Silicone prototypes looked promising as what was produced was an ellipse with a flat central web which, if cut correctly, could be used to create an aperture bar to prevent the epiglottis falling into the distal aperture. The silicone prototype was also smooth and deflated into a wafer thin ellipse, however, the silicone mask was unable to retain the desired bowl shape and it was no longer possible to make rapid adjustments to the design. The silicone Dunlop prototype was superior to the Goldman prototype, one of Brains first prototypes created from the cuff of a latex Goldman dental mask, however Brain needed a material that would give him design flexibility before the next set of silicone moulds were cast. In 1986, Brain continued to make prototypes from latex with a range of modifications; the inclusion of an inflation line, a thin-walled elliptical ring in the cuff which resulted in equal expansion of the cuff, the creation of a larger size to increase the reliability of cuff seal pressure and a moulded back plate for the cuff. By December 1986, Brain was ready to conduct the first wholly independent trial and chose Dr John Nunn to be the recipient of the silicone prototypes to conduct the trial. "There were three outstanding advantages of the LMA in patients who breathed spontaneously. Firstly, excellent airway patency was obtained in 98% of patients and did not deteriorate during the course of the anaesthetic. Secondly, as no manual support of the jaw was necessary the hands of the anaesthetist were freed for monitoring, record keeping and other tasks. Thirdly, it was possible to maintain a clear airway throughout transfer of the patient to the recovery room." The publication of this trial in 1989 was critical in kickstarting the uptake of the laryngeal mask in the UK".
First commercial laryngeal mask
On 5 December 1987, Brain received the first case of all-factory-made, silicone cuffed, LMA Classic laryngeal mask distributed by The Laryngeal Mask Company Limited. The LMA Classic was launched in the UK and the British anaesthesia community were quick to realise the potential benefits of the laryngeal mask. Within 3 years of launch in the UK, the device had been used in at least 2 million patients and was available in every hospital. By 1992, the laryngeal mask was approved for sale and being sold in Australia, New Zealand, South Korea, Hong Kong, Taiwan, Malaysia, India and the United States. The anaesthesia community had been calling for practice guidelines and in 1992 the ASA commissioned a task force to establish practice guidelines for managing difficult airway situations. The ASA algorithm for difficult airways was published in 1993 and stressed an early attempt at insertion of the laryngeal mask if face mask ventilation was not adequate. The laryngeal mask revolutionised anaesthetic practice and by 1995 had been used in excess of 100 million patients and was available in more than 80 countries throughout the world. The laryngeal mask had now been widely accepted as a form of airway management.
Between 1989 and 2000 a variety of specialised laryngeal masks were released which included the LMA Flexible™ (1990), LMA Fastrach™ (1997), LMA Unique™ (1997) and LMA ProSeal™ (2000), all offered by The Laryngeal Mask Company.
- LMA International N.V. Annual Report 2011, pp. 15
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- Joseph R. Brimacombe, Laryngeal Mask Airway: Principles and Practice, Second Edition (2005), pp. 12
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- Joseph R. Brimacombe, Laryngeal Mask Airway: Principles and Practice, Second Edition (2005), pp. 16–20
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- Brain AIJ, Denman WT, Goudsouzian NG (1999). Laryngeal Mask Airway Instruction Manual. San Diego, Calif: LMA North America Inc.
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- Experimental laryngeal masks made during its development, howequipmentworks.com Retrieved 18 October 2014