The LMA was originally designed to facilitate ventilation during anesthesia for short operating room procedures. It has been shown to provide improved ventilation in cardiac arrest and failed airway cases and has a shallow learning curve, promoting its use by relative novices.
The LMA consists of a short curved tube connected to a small mask with inflatable cuff. The shape promotes blind insertion with an endpoint detected as resistance as the leading edge of the cuff just enters and obstructs the esophageal inlet. The inflated cuff then seals around the laryngeal inlet. The distal “mask” incorporates a small grate to prevent prolapse of the epiglottis within the mask. The LMA has several configurations, including a disposable model, the LMA Unique (see Figs. 22.58 and 22.59), and a model that facilitates blind oral intubation, the intubating LMA, or I-LMA (see Fig. 22.64 in next section). LMAs are available in three adult sizes: #3 (30-50 kg), #4 (50-70 kg), and #5 (>70 kg). They are also available in pediatric sizes from size 0 to 2.5 for infants through toddlers.
LMA Unique. Adult sizes 3, 4, and 5 and pediatric size 2.5 are seen here. (Photo contributor: Lawrence B. Stack, MD.)
LMA Unique. The laryngeal surface of the LMA Unique with inflated cuff. Note the “grate,” which prevents epiglottic prolapse into the mask. (Photo contributor: Lawrence B. Stack, MD.)
The LMA is inserted into the mouth and held against the hard palate while being advanced into the hypopharynx (see Fig. 22.60). The LMA is advanced until resistance is met, and the cuff is then inflated with 20 to 40 mL of air to effect a seal (see Fig. 22.61). The mask should be lubricated prior to insertion.
LMA Insertion. LMA with deflated cuff is held against the hard palate during insertion by the index and third fingers. (Photo contributor: Lawrence B. Stack, MD.)
Correct LMA Placement. The LMA is correctly seated when resistance is met. Slight adjustments may be needed once seated. (Photo contributor: Lawrence B. Stack, MD.)
Because the LMA aligns with the glottic opening, it is possible to intubate the trachea through the LMA with minimal interruption of ventilation. The distal grate prevents anything larger than a 6.0 internal diameter (ID) ETT through a #3 and #4, and a 7.0 ID ETT through a #5. In addition to passing a small ETT directly, it is also possible to pass a flexible fiberoptic scope or a rigid fiberoptic scope ...