A laryngeal mask airway (LMA), also known as laryngeal mask, is a medical device that keeps a patient's airway open during anaesthesia or while they are unconscious. It is a type of supraglottic airway device. They are most commonly used by anaesthetists to channel oxygen or inhalational anaesthetic to the lungs during surgery and in the pre-hospital setting (for instance by paramedics and emergency medical technicians) for unconscious patients. 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. The laryngeal mask was invented by British anaesthesiologist 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.
Uses It channels oxygen and inhalational anaesthetic to the lungs. It can be used during anaesthesia, or while a patient is unconscious. Laryngeal mask airways are designed to be an easy way to secure the airway and ventilate a patient – they are easier to place than tracheal intubation due to the lack of muscle relaxants and laryngoscopy. They are also less likely to damage teeth or the larynx itself. It may form an air-tight seal. Cuffs are available in multiple sizes. LMAs can be alternatives to the use of a face mask when using a bag-valve-mask device to prevent gastric insufflation.
Contraindications A laryngeal mask airway is generally not used in surgeries where there is a high risk that stomach contents may be aspirated. This is particularly for surgeries that last longer than 2 hours. It often uses low inflation pressures, so may not be appropriate in patients with illnesses that cause low lung compliance. As it is typically larger and more obstructive than tracheal intubation, it is generally not used for surgery of the mouth and throat. It is not used for conscious patients because of the risk of stimulating the gag reflex.
Complications A laryngeal mask leaves more anatomical dead space in the trachea than with tracheal intubation. This can decrease the oxygenation of the lungs and the removal of carbon dioxide. It also slightly increases airway resistance. More serious complications include vomiting while the laryngeal mask airway is in place (potentially leading to aspiration of stomach contents). Although the laryngeal mask airway is specifically designed to be easy to place, it is possible for the ventilation it provides to be inadequate. This may be due to variations in neck anatomy, abnormal neck position, dislodgement of the cuff, the mask not being long enough to reach the larynx (or more rarely too long), or folding of the mask in the pharynx. For these reasons, radiology can be used to ensure that the laryngeal mask airway is in the correct position.
Technique A laryngeal mask airway has an airway tube that connects to an elliptical mask with a cuff. The cuff can either be an inflating type (achieved after insertion using a syringe of air), or self-sealing. A laryngeal mask airway is first completely sterilised (it may be reused many times). Standard checks for common use defects are performed (such as cracks in the plastic). For an inflatable cuff, the cuff is inflated and deflated outside the patient to ensure it is functional. A pen-like grip is used to move it through the patient's mouth and throat, preferably when their head is extended to straighten the airway. The laryngeal mask airway is lubricated so that it can be placed more easily. 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. The tip of the laryngeal mask sits in the throat against the upper oesophageal sphincter.
History
Concept Archie Brain began studying the anatomy and physiology of the upper airway in relation to existing airways. Brain concluded that current techniques for connecting artificial airways to the patient were not ideal. He reasoned 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 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.
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