Laryngeal Mask Airway

The laryngeal mask airway (LMA) is a supraglottic airway device developed by British Anesthesiologist Dr. Archi Brain. It has been in use since 1988. Initially designed for use in the operating room as a method of elective ventilation, it is a good alternative to bag-valve-mask ventilation, freeing the hands of the provider with the benefit of less gastric distention. ^{[1, 2]} Initially used primarily in the operating room setting, the LMA has more recently come into use in the emergency setting as an important accessory device for management of the difficult airway. ^{[3, 4]}

The LMA is shaped like a large endotracheal tube on the proximal end that connects to an elliptical mask on the distal end. It is designed to sit in the patient’s hypopharynx and cover the supraglottic structures, thereby allowing relative isolation of the trachea. The patient should be obtunded and unresponsive before one of these devices is placed.

The LMA is a good airway device in many settings, including the operating room, the emergency department, and out-of-hospital care, because it is easy to use and quick to place, even for the inexperienced provider. ^{[5, 6, 7]} A success rate for placement of a LMA of nearly 100% occurs in the operating room. A lower rate of achievement for LMA placement may be expected in the emergency setting. ^[8] Its use results in less gastric distention than with bag-valve-mask ventilation, which reduces but does not eliminate the risk of aspiration. ^{[9, 10]} This may be particularly pertinent in patients who have not fasted before being ventilated.

Laryngeal mask airways come in several types, as follows:

• The LMA Classic is the original reusable design.

• The LMA Unique is a disposable version, making it ideal for emergency and prehospital settings. ^[11]

• The LMA Fastrach, an intubating LMA (ILMA), is designed to serve as a conduit for intubation. ^[12] Although most LMA designs can serve this purpose, the LMA Fastrach has special features that increase the rate of successful intubation and do not limit the size of the endotracheal tube (ETT). These features include an insertion handle, a rigid shaft with anatomical curvature, and an epiglottic elevating bar designed to lift the epiglottis as the ETT passes.

• The LMA Flexible has softer tubing. It is not used the in the emergency setting.

• The LMA ProSeal has the addition of a channel for the suctioning of gastric contents. It also allows for 50% higher pressures without a leak. However, it does not permit blind intubation and is not currently used in the emergency setting.

• The LMA Supreme, which is a newer design, is similar to the ProSeal and has a built-in bite block. ^[11]

• Another newer design is the LMA CTrach, which inserts like the LMA Fastrach and has built-in fiberoptics with a video screen that affords a direct view of the larynx.

Elective ventilation

The laryngeal mask airway (LMA) is an acceptable alternative to mask anesthesia in the operating room. It is often used for short procedures when endotracheal intubation is not necessary. ^[1]

Difficult airway

After failed intubation, the LMA can be used as a rescue device. ^{[13, 14]}

In the case of the patient who cannot be intubated but can be ventilated, the LMA is a good alternative to continued bag-valve-mask ventilation because LMA is easier to maintain over time and it has been shown to decrease, though not eliminate, aspiration risk. ^{[9, 10]}

In the case of the patient who cannot be intubated or ventilated, a surgical airway is indicated and should not be delayed. However, if the LMA is at hand, it can easily be attempted quickly, while an assistant simultaneously prepares for cricothyroidotomy. ^[8]

Cardiac arrest

The 2005 American Heart Association guidelines indicate the LMA as an acceptable alternative to intubation for airway management in the cardiac arrest patient (Class IIa). ^{[9, 15]} This may be particularly useful in the prehospital setting, where emergency medical technicians typically have less experience with intubation and lower success rates. ^{[16, 17]}

Conduit for intubation

The LMA can be used as a conduit for intubation, particularly when direct laryngoscopy is unsuccessful.

An ETT can be passed directly through the LMA or ILMA. Intubation may also be assisted by a bougie or fiberoptic scope. ^[18]

Prehospital airway management

The LMA is useful in the prehospital setting not only for patients in cardiac arrest but also for managing a difficult airway.

In patients in whom positioning or prolonged extrication does not allow for endotracheal intubation, the LMA can be inserted and allow for successful airway management until a definitive airway can be established. ^[9]

The widespread use of LMA in the prehospital setting in Japan for cardiac arrest has shown it to be an effective and relied upon method for establishing emergency airways. ^[19]

Pediatric use

Laryngeal mask airways are available in a range of pediatric sizes.

Absolute contraindications (in all settings, including emergent) are as follows:

• Cannot open mouth

• Complete upper airway obstruction

Relative contraindications (in the elective setting) are as follows:

• Increased risk of aspiration: Prolonged bag-valve-mask ventilation, morbid obesity, second or third trimester pregnancy, patients who have not fasted before ventilation, upper gastrointestinal bleed

• Suspected or known abnormalities in supraglottic anatomy

• Need for high airway pressures (In all but the LMA ProSeal, pressure cannot exceed 20 mm water for effective ventilation.)

Laryngeal mask airway (LMA) insertion is facilitated by sedation. Propofol (Diprivan) or midazolam (Versed) are acceptable choices. ^[6]  For elective ventilation in the operating room, less anesthesia is typically required for insertion and maintenance of the LMA than for endotracheal intubation. ^[6]  In the emergency setting, the patient is often obtunded or unconscious, and further sedation may not be necessary for LMA insertion. The risk of inadequate sedation is triggering laryngospasm. For more information, see Procedural Sedation.

Paralysis is not necessary for LMA insertion and maintenance.

Movement and coughing upon insertion should be particularly avoided in patients who are at risk for cervical spine injuries; therefore, adequate anesthesia is particularly important in these patients.

Children may require deeper anesthesia.

Equipment is as follows:

• Laryngeal mask airway (LMA), shown below

  LMA Classic. Image courtesy of LMA North America.

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  LMA Fastrach. Image courtesy of LMA North America.

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• Appropriately sized syringe for cuff inflation (included in LMA kit)

• Water-soluble lubricant (included in LMA kit)

• Bag-valve mask

• Oxygen source

• Yankauer suction device

• End-tidal carbon dioxide (E_T CO₂) detector

• Intubation equipment and a cricothyroidotomy kit (These items should be close at hand.)

The optimal head position for insertion of the laryngeal mask airway (LMA) is sniffing position. ^[6]

The optimal head position for insertion of the intubating laryngeal mask airway (ILMA) is neutral position. ^[6]

Preparation

Preoxygenate the patient with 100% oxygen via a nonrebreather mask, as time allows.

Choose the appropriate size of laryngeal mask airway (LMA).

Check the LMA cuff for leaks.

Deflate the cuff of the LMA completely against a flat surface.

Apply a water-soluble lubricant generously to the posterior surface of the mask.

Administer sedation when indicated.

Position the patient.

Cricoid pressure

Cricoid pressure is intended to reduce the risk of aspiration, although its effectiveness is debated. ^{[20, 21]}

Decreased rates of successful insertion have been seen with application of cricoid pressure. ^{[5, 6, 7]} Therefore, if cricoid pressure is applied, it may need to be released in order to properly position the LMA or intubate through the intubating laryngeal mask airway (ILMA).

Insertion of the LMA

Hold the LMA like a pen, with the index finger of the dominant hand at the junction of the mask and the tube, as shown below.

Slide the LMA along the hard palate, pushing it back against the palate as it is advanced toward the hypopharynx, as in the image below. This prevents the tip from folding over on itself and reduces interference from the tongue.

Advance with gentle pressure until resistance is met.

If necessary, continue pressure on the tube with the nondominant hand to fully advance the LMA to its proper position.

Once in place, inflate the cuff without holding the LMA to allow it to acquire its natural position.

Approximately 8 cm of the tube protrudes from the patient’s mouth.

The video below depicts LMA insertion.

Insertion of the intubating laryngeal mask airway (ILMA)

Hold the ILMA by the handle.

Insert the mask into the patient’s mouth and push it back against the hard palate, as shown below.

Slide the mask backward, following the curve of the tube.

Swing the ILMA into place.

Inflate the cuff as with the LMA.

Insertion of the LMA ProSeal

Insert this model like the original LMA or attach it to a rigid insertion handle and insert it like an ILMA.

An alternate method is to use a bougie by placing it into the drainage tube and passing it deliberately into the esophagus under direct laryngoscopy.

Advance the ProSeal over the bougie into position.

Confirming placement

Confirm the position of the LMA by auscultating bilateral breath sounds and an absence of sounds over the epigastrium, observing chest rise with ventilation, and placing an E_T CO₂ to look for color change.

Ensure that the vertical black line on the tube is at the patient’s midline.

Assess for ability to generate up to 20 cm of water pressure without a leak.

Intubating through the LMA and ILMA

Intubation through an intubating LMA such as the LMA Fastrach produces higher success rates than intubating through a standard LMA (approximately 95% and 80%, respectively). ^[8]

The LMA Classic and LMA Unique limit the size of the endotracheal tube (ETT) that can be passed. A 6.0 ETT fits through LMA sizes 3 and 4. LMA sizes 5 and 6 accommodate an ETT up to 7.0.

Inspect the ETT and lubricate it well.

Pass it through the lumen of the LMA tube into the trachea until intubation is complete.

Confirm placement, as shown below.

A bougie or fiberoptic scope may be used to assist intubation.

The ETT is included with the LMA Fastrach, but a standard ETT can also be used.

Once the patient is intubated, the ILMA can be removed by deflating the cuff and passing it over the tube using a stabilizer rod, as shown.

As an alternative to the standard insertion technique described above, there is evidence that laryngoscope-guided placement of the LMA results in higher initial success rates. ^[22]

To optimize proper positioning, make sure the mask is completely deflated, with a smooth, well-lubricated surface. Placing the mask face down on a flat surface such as a table helps achieve proper deflation.

If insertion is unsuccessful with cricoid pressure, release pressure and reattempt insertion.

If the initial laryngeal mask airway (LMA) placed does not result in a good seal, attempt the next larger size. In general, if a patient is between sizes, choose the larger size.

When intubating through the ILMA, advance the endotracheal tube (ETT) until it is about to emerge from the LMA (near the 15-cm mark). Then, lift up on the handle as the ETT is advanced into the trachea to complete intubation. This is known as the Verghese maneuver after Dr. Chandy Verghese.

Although the LMA can be left in place after intubation, removing it promptly helps minimize upper airway trauma.

Rare complications due to laryngeal mask airway (LMA) insertion occur in the operating room. The rate of complications was 0.15% in a large study, ^[23] but the rate is likely to be higher in the emergency setting. Such complications include the following:

• Aspiration of gastric contents

• Local irritation

• Upper airway trauma: Pressure-induced lesions, nerve palsies

• Mild sympathetic response

• Complications associated with improper placement: Obstruction, laryngospasm

• Complications associated with positive-pressure ventilation ^[24] : Pulmonary edema, bronchoconstriction

• Transient unilateral lingual nerve injury ^[25]

A table showing laryngeal mask airway size based on patient weight is included below.

Table. Laryngeal Mask Airway Size Based on Patient Weight (Open Table in a new window)