critical care medicine
Airway and Respiratory Devices
Laryngeal Mask Airways (LMA)
Supraglottic airways (SGAs) are inserted into the pharynx to allow ventilation, oxygenation, and administration of anesthetic gases without the need for endotracheal intubation. These devices are used for the following: Primary airway management Rescue ventilation when bag-valve-mask ventilation is difficult Rescue ventilation when definitive airway management is expected to be difficult (eg, with anatomic abnormalities) Ventilation when personnel are limited (eg, prehospital) As a conduit for endotracheal intubation The SGAs used most commonly in the operating room are the laryngeal mask airways (LMAs) and similar devices, while other SGAs are used more commonly in the emergency department and for prehospital airway management (see Other Devices ). LMAs are inserted into the lower oropharynx to prevent airway obstruction by soft tissues and to create an effective channel for ventilation (see figure). A variety of available LMAs allow passage of an endotracheal tube or a gastric decompression tube. As the name implies, these devices seal the laryngeal inlet (rather than the face-mask interface) and thus avoid the difficulty of maintaining an adequate face-mask seal and the risk of displacing the jaw and tongue. Complications include vomiting and aspiration in patients who have an intact gag reflex, who are receiving excessive ventilation, or both. There are numerous techniques for LMA insertion (see How To Insert a Laryngeal Mask Airway ). The standard approach is to press the deflated mask against the hard palate (using the long finger of the dominant hand) and rotate it past the base of the tongue until the mask reaches the hypopharynx so that the tip then sits in the upper esophagus. Once in the correct position, the mask is inflated. Inflating the mask with half the recommended volume before insertion stiffens the tip, possibly making insertion easier. Some mask versions replace the inflatable cuff with a gel that molds to the airway. Although a laryngeal mask airway does not isolate the airway from the esophagus as well as an endotracheal tube, it has some advantages over bag-valve-mask ventilation: It minimizes gastric inflation It provides some protection against passive regurgitation Most versions of LMAs have an opening through which a small tube can be inserted to decompress the stomach. The efficacy of the airway seal with an LMA, unlike endotracheal tubes, is not directly correlated with the mask inflation pressure. With endotracheal tubes, higher balloon pressure causes a tighter seal; with an LMA, overinflation makes the mask more rigid andlessable to adapt to the patient’s anatomy. If the seal is inadequate, mask pressure should beloweredsomewhat; if this approach does not work, a larger mask size should be tried. In emergencies, laryngeal mask airways should be viewed as bridging devices. Prolonged placement, overinflation of the mask, or both may compress the tongue and cause tongue edema. Also, if noncomatose patients are given Drugs to cause paralysis for intubation before LMA insertion (eg, for laryngoscopy), they may gag and possibly aspirate when such drugs wear off. Either the device should be removed (assuming ventilation and gag reflexes are adequate), or drugs should be given to eliminate the gag response and provide time for an alternative intubation technique. A contraindicationto use of an LMA is massive facial trauma. The LMA is a tube with an inflatable cuff that is inserted into the oropharynx. A: The deflated cuff is inserted into the mouth. B: With the index finger, the cuff is guided into place above the larynx. C: Once in place, the cuff is inflated. Some cuffs use a gel that molds to the airway rather than an inflatable cuff. 