Supraglottic airway devices (SADs), sometimes also called extraglottic airway devices, ...
- ... maintain upper airway patency (during general anesthesia),
- ... allow for limited intermittent positive pressure ventilation (IPPV),
- ... can be inserted/ placed atraumatically with a relatively low skill set,
- ... and offer some degree of protection against the aspiration of gastric contents.
The laryngeal mask was invented by Dr. Archibald ('Archie') Brain, a British anesthesiologist (or 'anaesthetist', to be precise) in the early 1980s and first came to market in the United Kingdom in 1987. Wikipedia has an excellent summary of how Dr. Brain developed the device.
Conincidentally, Propofol became widely available around the same time, which helped the laryngeal mask gain popularity quickly among practitioners. The reason for this is that Propofol works much better than other hypnotics, such as barbiturates, in suppressing laryngeal reflexes in non-paralyzed patients. It is therefore much easier to place a laryngeal mask after induction with Propofol than, for example, Thiopentone in patients who are not paralyzed and breathing spontaneously under general anesthesia.
The terminology for these devices can be confusing. The first laryngeal mask introduced in 1987 was the LMA classic, now also referred to as the classic LMA or cLMA, or simply LMA. The term 'LMA' (for 'laryngeal mask airway') is a registered trademark, and refers to the SADs marketed by LMA North America, Inc.
Many design modifications of the classic LMA are now available, such as the LMA ProSeal, LMA FasTrach,or the LMA Supreme. The LMA Unique is the disposable version of the LMA classic. The LMA classic can be sterilized and re-used for a certain number of cycles.
There are now many devices on the market made by other companies, for example the i-gel or AirQ. These have obvious design features of the original laryngeal mask airway but cannot be called an 'LMA' due to the trademark and copyright protection. Many clinicians still (incorrectly) refer to these devices as an 'LMA' in everyday practice, for example the 'i-gel lma' or the 'AirQ lma'..
Comparison to an ET tube
Compared to an ET tube SADs have advantages and disadvantages:
SADs can be divided into first and second generation devices.
Please refer to our section on AIRWAY TECHNQUES to read up on how to insert a laryngeal mask.
The invention of the LMA has arguably been the most impactful advancement in the field of airway management over the last 40 years. SADs are now widely used and their spectrum of application has extended significantly since first being used in the 1990s.
According to the fourth national audit project in the UK (NAP4), SADs are used in over half of all general anesthetics administered in that country (3).
Supraglottic airway devices can be a life-saving tool in a 'cannot intubate cannot ventilate' (CICV) scenario and are therefore an essential part of the difficult and failed intubation algorithms published by the American Society of Anesthesilogists (ASA) and the Difficult Airway Society (DAS). In addition, some SADs can be helpful in difficult intubations as a conduit for and ET tube, namely the LMA Unique together with an Aintree catheter or the AirQ laryngeal mask.
Limitations & Contraindications
While SADs/ laryngeal masks are very helpful devices which are used safely and successfully in thousand of surgeries every day, they are certainly not the best choice for every patient or every type of surgery.
When in doubt, intubate! Remember that there will be no gold medal for using an SAD successfully when endotracheal intubation would have been the safer choice. Always consider risks versus benefits.
Be aware of a number of contraindications, most of them relative, and limitations to the use of SADs:
- Full stomach: The risk for aspiration is reduced with second-generation devices, but not intubating a patient with a full stomach is indefensible. Pregnant patients at term are considered to have a full stomach. This is an absolute contraindication!
- Increased risk of regurgitation of gastric contents: This applies to patients with issues such as significant GERD, a hiatal hernia, diabetic gastroparesis, later stages of pregnancy, or morbid obesity, amongst others. Again, second-generation devices offer improved (but not complete) protection against aspiration. Using SADs in these patients is controversial rather than absolutely contraindicated.
- Non-supine positioning & limited intraoperative access to the airway: Always consider how you would re-insert an SAD if it became dislodged or lost its seal, which can happen during surgery. Could you access the airway easily? Again, using SADs in these patients is controversial rather than absolutely contraindicated.
- Obesity: Morbidly obese patients tend to not breathe well spontaneously without ventilator support during surgery. They also require higher airway pressures with pressure support modes or IPPV, and need higher PEEPs to prevent shunt. In addition, the risk of regurgitation is also higher compared to patients with normal BMIs. There isn't a defined threshold above which an SAD would be considered unsafe so use your clinical judgement.
- Intra-abdominal surgery: A reasonable amount of literature has been published describing the successful and safe use of SADs in abdominal and particularly in laparaoscopis surgery such as inguinal hernia repairs and cholecystectomies. It is probably fair to say that most practitioners would intubate these patients. Just because you can does not mean you should...
- Long duration of surgery: Again, there is no hard and fast rule on the length of time you would keep an SAD in situ, but many practitioners feel uncomfortable leaving this type of device in place for prolonged surgeries. The logic behind this reasoning is not immediately clear unless you can assume that the regurgitation/ aspiration risk is time-dependent.
- Muscle relaxation/ IPPV: I have come across a few clinicians who would not use an SAD in conjunction with any kind of positive airway pressure ventilation, even PEEP/ CPAP and pressure-support breath augmentation. A larger group will not use an SAD in paralyzed patients and always intubate when a muscle relaxant is being used. Again, use your clinical judgement and intubate if in doubt. This is the more conservative but easier-to-defend approach.
PERSONAL OPINION: SADs can safely be used with pressure-support ventilation modes and PEEP in patients and surgeries deemed suitable for using an SAD generally (see above). Within reason this applies to IPPV too, but I would limit this to a pressure-controlled ventilation mode and peak airway pressures certainly <20cmH2O. High peak airway pressures should definetely be avoided and a close eye must be kept on the laryngeal mask seal to detect a potential leak which would increase the risk of inadvertent gastric insufflation..
- Brain, A. I. J. (1983): The laryngeal mask- a new concept in airway management. In British Journal of Anaesthesia 55 (8), pp. 801–805. DOI: 10.1093/bja/55.8.801.
- Brain, A. I. J.; Verghese, C.; Strube, P.; Brimacombe, J. (1995): A new laryngeal mask prototype. In Anaesthesia 50 (1), pp. 42–48. DOI: 10.1111/j.1365-2044.1995.tb04513.x.
- Cook, T. M.; Woodall, N.; Frerk, C. (2011): Major complications of airway management in the UK. Results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1: anaesthesia. In British Journal of Anaesthesia 106 (5), pp. 617–631. DOI: 10.1093/bja/aer058.
- van Zundert, T. C. R. V.; Brimacombe, J. R.; Ferson, D. Z.; Bacon, D. R.; Wilkinson, D. J. (2012): Archie Brain. Celebrating 30 years of development in laryngeal mask airways. In Anaesthesia 67 (12), pp. 1375–1385. DOI: 10.1111/anae.12003.x.