Laryngeal Mask Airway

While the endotracheal tube (ETT) has served a preeminent role in airway management, use of the laryngeal mask airway (LMA), is becoming popular, especially in outpatient surgery and in the management of airway crises.  The LMA is designed to provide an "oval seal around the laryngeal inlet" once it is inserted and the cuff inflated. When inserted, it lies "at the crossroads of the digestive and respiratory tracts". The LMA is particularly useful where a mask fit is difficult, e.g., in bearded or edentulous patients or where both hands of the clinician need to be free. Patients need not necessarily be breathing spontaneously for the LMA to be of use; provided the patient has normal lungs and normal laryngeal anatomy (and a properly sized mask), positive pressure ventilation can be used. However, when peak airway pressures exceed 20 cm H2O, gas leaks around the cuff are more likely.

The LMA is potentially useful in a number of settings, such as the following:
• Fasted patients for short surgical cases not needing muscle relaxation & with little risk of regurgitation
• Difficult face mask fit (beards, edentulous)
• Need for free hands
• Special situations  (opera singers/rock stars/public speakers; difficult airway rescues )

The LMA is best inserted while deflated and well-lubricated under propofol anesthesia with the head and neck positioned as for normal intubation. With an assistant temporarily holding the mouth open until the widest part of the mask is past the teeth, or using the third finger of the inserting hand, the tip of the LMA is inserted into the mouth, pressing the tip against the hard palate as it is advanced cephalad into the pharynx with the right hand. Then, with the index finger positioned at the cuff/tube interface, the LMA is inserted as far as possible into the hypopharynx. Before removing the index finger, bring the other hand up to the connector and press gently but firmly in the cephalad direction. When resistance is felt, the tip of the cuff is positioned at the upper esophageal sphincter. After assuring that the black line on the LMA is facing the upper lip, the cuff is inflated. 

A number of potential contraindications to the LMA exist (not all of these contraindications are absolute):
• Full stomach/aspiration risk (including hiatus hernia)   
• Clinician untrained in LMA use
• Patients in the prone position    
• Morbidly obese patients   
• Oropharyngeal pathology expected to result in a poor LMA fit (e.g., radiotherapy for hypopharynx/larynx)
• Pharyngeal/glottic surgery (tonsillectomy OK)
• Need for PPV with peak airway pressures > 20 cm H2O (stiff lungs, Trendelenburg positionn, laparoscopy) [However, the LMA ProSeal is specifically designed to allow for PPV with much higher airway pressures].
• Very long cases    

The role of the LMA in patients who are suspected to be difficult to intubate is controversial. While some (perhaps most) authorities would emphasize awake intubation in such cases, others would consider carrying out attempted laryngoscopy after induction, with LMA placement if ETT placement is unsuccessful. Still others would recommend going directly with the LMA, avoiding laryngoscopy and attempted intubation.

For more information on the LMA go to http://www.anesthesia.utoronto.ca/English/page_3_5172_1.html
Figure: Illustration of the range of laryngeal mask airway (LMA) products.

Image Credit: http://www.vitaid.com/canada/lma/images/completerange.jpg