Supraglottic Airway Devices
After the introduction of the laryngeal mask airway (LMA) in 1988, supraglottic airway devices rapidly found a significant role in the management of the difficult airway. They are extensively reviewed by Cook. The classic LMA (cLMA) is a small latex mask mounted on a hollow plastic tube.[18,116,117,118,119,120,121] It is placed blindly in the lower pharynx overlying the glottis. The inflatable cuff on the mask helps wedge the mask in the hypopharynx so that it sits obliquely over the laryngeal inlet. Although the LMA produces a seal that will allow ventilation with gentle positive pressure, it does not definitively protect the airway from aspiration. Compared with an ETT, an LMA can be appropriately placed more rapidly and more successfully by operators with limited advanced airway skills.[122,123] The use of the LMA has been extensively studied in cardiac arrest situations and found to be superior to bag mask ventilation. The often quoted risk of pulmonary aspiration is probably overestimated; some reported aspiration probably occurs before insertion of the LMA. Concerns of inadequate ventilation (leakage of gas) or gastric inflation, however, remain. Ventilation is possible through the LMA if inflation pressures are kept relatively low. Increasing peak airway pressure from 15 cm H2O to 30 cm H2O may increase the proportion of gas leakage from 13% to 27% and, more importantly, increase the proportion entering the esophagus from 2% to 35%.
Modifications of the cLMA include the intubating LMA (ILMA), the Proseal LMA (Intavent Orthofix, Maidenhead, Berkshire, UK), and various disposable LMAs. The ILMA (Fig. 4) has a more rigid, wider tube with a handle for insertion.[126,127,128,129] A modified tracheal tube with a low profile cuff can be passed through the ILMA into the trachea either blindly or with the aid of a fiberoptic scope. A bar overlying the lower aperture lifts the epiglottis forward revealing the laryngeal inlet and facilitating intubation. The ILMA may be suitable in the management of trauma patients in situations of limited access or when cervical spine injury is suspected.
The intubating laryngeal mask airway. Reproduced with permission from Brain AIJ, Verghese C: Laryngeal Mask Airway (LMA)-Fastrach Instruction Manual. San Diego, LMA North America, 1998.
The Proseal LMA was introduced in 2002 as a device to ensure better airway protection and more successful ventilation. It differs from the cLMA in having a larger deeper mask and a posterior cuff. A drain tube reduces the possibility of leaked gases entering the esophagus and acts as a vent if regurgitation occurs.
Crit Care Med. 2008;36(7):2163-2173. © 2008 Lippincott Williams & Wilkins
Cite this: The Difficult Airway in Adult Critical Care - Medscape - Jul 01, 2008.