SUPRAGLOTTIC AIRWAY DEVICES
Compared to an endotracheal tube (ETT), supraglottic airway devices are considered less secure due to the lack of an inflated cuff protecting the larynx, trachea, and distal airways. Although the supraglottic airways are useful for gas exchange, use of these devices can place the patient at risk for laryngospasm and aspiration of gastric contents. Despite these disadvantages, supraglottic airway devices have an important role in the difficult airway algorithm. When ventilation by face mask proves difficult or impossible, use of a supraglottic airway for rescue ventilation can be life-saving.
For the last three decades, supraglottic airway devices have been gaining popularity worldwide in both the hospital and prehospital settings. While there are several models available, all possess the same essential design components: (1) a seal formed in the pharynx, isolating the respiratory tract from the gastrointestinal tract; (2) an external tube for connection to an oxygen supply and a ventilation device; and (3) a blind insertion technique that requires confirmation of adequate ventilation. There are two main categories of supraglottic airways: periglottic devices that form a seal around the larynx and esophageal obturator devices that block the esophagus and divert gas flow to the respiratory tract.
The Laryngeal Mask Airway (LMA) is a periglottic airway device with a curved tube connected to a diamond tear-drop (oval) shaped cuff. The device is available in rubber autoclave-safe and disposable models. Both types are designed to sit in the posterior pharynx over the larynx (glottic vestibule) and a fenestrated epiglottic bar in the bowl prevents epiglottic obstruction. The LMA is typically recommended for shorter duration operations, less than 2 hours; however, it is commonly used for longer cases. Standard ETT insertion is possible with all LMAs, except for flexible ones, either blind or with fiberoptic guidance.
Given the increased risk of gastric content aspiration, airway pressures should be kept below 20 cm H2O to prevent gastric distention. Cuff inflation pressure should be kept below 60 cm H2O. Similarly, patients with “full stomach” status (such as those with poorly controlled GERD, hiatal hernia, gastric neuropathy, pregnancy) or pharyngeal obstruction are not candidates for an LMA. Due to related concerns, using the LMA in patients in prone position is controversial since it is not considered a secure airway.
The LMA Classic is popularly stocked in most operating rooms in the United States. It is available in sizes 1, 1.5, 2, 2.5, 3, 4, 5, and 6. This LMA is designed for single use. It is now listed in the ASA Difficult Airway Algorithm as an airway ventilatory device or a conduit to endotracheal intubation. A distinct disadvantage with Classic LMAs is that only small ETTs can be inserted, which if needed should be changed to a larger ETT with the help of tube exchangers.
The Flexible LMA has a small diameter tube that is wire reinforced, enabling it to be positioned out of midline ...