DISPOSABLE LARYNGEAL AIRWAY MASK (LMA)

General Information

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.  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.

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 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.  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.  Its use results in less gastric distention than with bag-valve-mask ventilation, which reduces but does not eliminate the risk of aspiration.  This may be particularly pertinent in patients who have not fasted before being ventilated.

Laryngeal mask airways come in several types.

·         The LMA Classic is the original reusable design.

·         The LMA Unique is a disposable version, making it ideal for emergency and prehospital settings.

·         The LMA Fastrach, an intubating LMA (ILMA), is designed to serve as a conduit for intubation. 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.

·         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 larynex.

Indications:

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.

Difficult airway

·         After failed intubation, the LMA can be used as a rescue device.

·         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.

·         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.

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).

·         This may be particularly useful in the prehospital setting, where emergency medical technicians typically have less experience with intubation and lower success rates.

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.

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.

·         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.

Pediatric use

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

Contraindications:

Absolute contraindications (in all settings, including emergent)

·         Cannot open mouth

·         Complete upper airway obstruction

Relative contraindications (in the elective setting)

·         Increased risk of aspiration

o   Prolonged bag-valve-mask ventilation

o   Morbid obesity

o   Second or third trimester pregnancy

o   Patients who have not fasted before ventilation

o   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 H2O for effective ventilation.)

Anesthesia:

Sedation

·         Laryngeal mask airway (LMA) insertion is facilitated by sedation.

·         Propofol (Diprivan) or midazolam (Versed) are acceptable choices.

·         For elective ventilation in the operating room, less anesthesia is typically required for insertion and maintenance of the LMA than for endotracheal intubation.

·         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.

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.