AIRWAY ASSET Laryngeal mask airways provide a natural conduit from the patient's lungs to the anesthesia machine, allowing for oxygenation, ventilation and administration of inhaled anesthetics.

Fewer sore throats in recovery, improved oxygenation, spontaneous ventilation and better management of difficult airways — the laryngeal mask airway has revolutionized anesthesia care since its introduction in the late '80s. The device's basic design has evolved from a hands-free way to ventilate an anesthetized patient without endotracheal tube intubation to a life-saving device available in many unique configurations. Let's explore best practices for using and caring for this airway management staple.

Developing designs
When originally developed, the LMA was a heat-sterilizable, reusable device made of silicone. Today, single-use devices are also available, which most clinicians prefer, citing concerns of device breakdown over time and the possibility of patient cross-contamination with reuse.

The original LMA, and devices like it, are currently known as "classic" models. They provide low-pressure seals around the glottic aperture to facilitate oxygenation and ventilation. In patients with known difficult airways, intubating LMAs provide an easy-to-use system designed to intubate the trachea with an endotracheal tube advanced through the LMA's ventilation channel. This can be done blindly or with videoscopic assistance on some models.

Some LMAs have been developed with separate channels through which an orogastric tube can be advanced into the stomach for decompression of acid or air. Flexible LMAs provide ventilation lumens that are wire-reinforced, which increase the flexibility of the tube without disrupting the seal at the glottis. These devices are often used in eye or ENT procedures, because the ventilation channel can be manipulated out of the surgical field without compromising ventilation. Some LMAs also have integrated bite blocks, which prevent occlusion of the ventilation channel by reflexive masseter spasm during emergence.

There are many clinical benefits associated with LMA use. In procedures requiring general anesthesia without muscle paralysis, the LMA is an outstanding tool that allows spontaneous ventilation. It provides the benefits of mask ventilation without such drawbacks as leaks or poor mask seals. In patients with known or unanticipated difficult airways, it can be used as a rescue device to provide ventilation and oxygenation. It has become the go-to device in scenarios where intubation is not possible and mask ventilation is challenging.

The LMA also provides a conduit for intubation, because the opening of the device usually rests directly above the vocal cords and glottis. In patients with poor dentition, the LMA allows placement of a secure airway without requiring the use of a laryngoscope, potentially limiting iatrogenic periodontal trauma.

LMAs can be used in almost all types of surgical procedures requiring general anesthesia and across all age groups. The LMA has become a critical piece of the American Society of Anesthesiologists' difficult airway algorithm. The ASA recommends LMAs when initial attempts at intubation have failed and mask ventilation is inadequate.

There are limitations to LMA use, including:

• procedures requiring muscle relaxation:
• laparoscopic procedures, because abdominal insufflation pressures may limit the adequacy of spontaneous ventilation;
• patients who are morbidly obese or have significant histories of untreated gastroesophageal reflux disease;
• patients deemed to have full stomachs, because the device does not offer any protection against aspiration of gastric contents.

Before use, visually inspect LMAs to ensure there are no obvious defects, and that the ventilation channel is patent. Deflate the cuff fully, and slowly re-inflate it to check for leaks. Selecting the correct LMA size is usually weight-based, but sizing up or down may be necessary to account for differences in individual patient oropharyngeal anatomy and mouth opening. Proper placement technique includes extending the head and neck and opening the mouth, followed by placing the device into the oropharynx in a single smooth motion. Take care to prevent folding the tip of the device onto itself and intrinsic obstruction from the tongue.

BACK TO BASICS
Tips for LMA Success

CLOSE WATCH Monitor reservoir bags and capnography waves to ensure airways remain patent.

Propofol is the best induction agent for laryngeal mask airway patients; it suppresses airway reflexes, and allows for insertion without the patient coughing or moving unexpectedly. After insertion, test the airway's patency using gentle hand ventilation, which should cause the patient's chest to rise without airway noise or audible air leak. The patient should complete unobstructed exhalation, with the anesthetic reservoir bag filling rapidly. The patient's oxygen saturation level should be stable and the capnography wave should be square in shape.

A sloped capnography wave indicates an airway obstruction. A reservoir bag that fails to fill rapidly indicates a partial airway obstruction. A bag that fails to fill at all indicates a large anesthetic gas leak. If any of these occur, remove the LMA and try reinserting it again. Secure the LMA in place with tape so it doesn't move outward. When attaching the breathing circuit, ensure that it doesn't pull on the LMA enough to cause displacement. Ensure the anesthesia circuit's reservoir bag is always in plain sight and proper alarms on the anesthesia machine are activated to ensure this rare but potential issue is quickly detected. Disconnect the circuit when patients need to be repositioned mid-procedure. Reattach it when the repositioning is complete, and recheck the airway's patency.

Insert a bite block — a roll of gauze between the lateral teeth works well — to help secure the device in place and prevent the patient from biting down during emergence. After surgery, keep the LMA in place until the patient emerges from anesthesia and can open and close her mouth on command. That's typically when protective airway reflexes have recovered.

— Daniel Cook

Source: "The Laryngeal Mask Airway" in Update in Anaesthesia (tinyurl.com/ohs9oe4)

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Today's anesthesia providers can't imagine a world without LMAs. They've become a critical tool in outpatient anesthetics, with established uses across all surgical disciplines. The many unique LMA configurations allow for the use of a device that is patient- and procedure-specific, for delivering optimal anesthetics and for achieving excellent surgical outcomes.