Laryngeal Mask Airways (LMA)
Laryngeal mask airways, or LMAs, have been in use since 1988. Since it can be very difficult to intubate some patients, especially in an emergency situation, this device was developed as an alternative to endotracheal intubation, but without the level of risk associated with intubation. LMAs cause less gastric distention and are less likely to induce aspiration in the patient. It has many advantages that make it ideal for certain situations, such as when the patient will not be intubated for long or when placement of an ET tube is not feasible.
One of the advantages is that less experienced providers can easily place the LMA. It doesn’t require the level of skill that inserting an ET tube does, and it is a step above bag valve mask ventilation. When you use the bag valve mask, you inevitably have to put one hand on the mask to hold it in place; however, with an LMA, you can place the tube and use both hands to work the bag. This allows for effective ventilation without the technical difficulties of an ET tube or a bag valve mask. All providers should learn how to use one of these devices to help secure an advanced airway.
What is a LMA?
An LMA is a supraglottic device. This means that when inserted correctly, it sits above the glottis in the hypopharynx. The tube itself resembles an ET tube on the proximal end and can be easily attached to an Ambu bag. At the distal end is an elliptical-shaped mask that delivers air down through the trachea and into the lungs, while blocking the esophagus at the same time to prevent air from causing gastric insufflation. Although this device was originally designed for use in short elective surgeries as an alternative to endotracheal intubation, its ease of use means that it has become a standard tool of paramedics and non-ET trained professionals. It allows for fast and accurate placement, regardless of circumstances.
This is primarily due to its construction. The user merely has to guide the elliptical end down into the back of the throat, where it fits snugly and allows air to enter the trachea but not the esophagus. This prevents air from entering into the stomach. The LMA can even be used on patients who were not NPO prior to insertion. In addition, the LMA can also be used as a guide to assist with ET tube placement. The provider can simply work the ET tube down the LMA and into the lungs.
How to Use an LMA
You should start by preoxygenating the patient with 100 percent oxygen as time allows. In operating room settings, the patient should be sedated for this procedure, but patients in emergency situations are often unconscious. If the patient is obtunded, then you can insert the LMA without sedation. You should use the enclosed syringe to check the inflation of the cuff prior to insertion. Be sure to remove all of the fluid and air from the cuff before positioning the LMA. The patient’s head should be in the sniffing position (this position is contraindicated in cases of suspected spinal trauma).
You should thoroughly lubricate the LMA, and it should be held like a pen behind the mask portion of the device. Insert along the hard palate to avoid collapsing the mask and to minimize blockage by the tongue. Continue to insert the device until resistance is felt. Once you feel the tube is in place, inflate the cuff to set the LMA in its proper position. Approximately 8 cm of tube should protrude from the patient’s mouth. Once the cuff is inflated, connect the bag to the tube to begin ventilating the patient.
Contraindications, Side Effects, and Precautions
LMAs are contraindicated in patients who cannot open their mouths or have complete upper airway obstruction. You should also avoid positioning the head in the sniffing position if you suspect the patient has suffered an injury to the cervical spine. The jaw thrust may be useful in this situation, but research is not clear on the effectiveness of LMAs with spinal precautions. Although this is a safe procedure, some complications have been seen. One is aspiration of gastric contents. This is more likely in an emergency situation with a patient who has not been NPO. However, aspiration is less likely with an LMA than with a bag valve mask.
Localized trauma in the upper airway is possible, and certain nerve palsies may occur secondary to placement. As with other advanced airways, the risk of pressure lesions in the airway is also a consideration. There may also be a mild sympathetic response with activation of the vagus nerve during the insertion of this device. When the LMA is not placed properly, laryngospasm and obstruction of the airway are two possible consequences that can occur. It is important to check the placement of an LMA by listening for bilateral lung sounds in the same way ET tube placement is checked. Finally, with positive pressure ventilation, pulmonary edema and bronchoconstriction are possible.