Airway Evaluation and Management - Laryngeal Mask Airway

Laryngeal Mask Airway

The classic LMA and its multiple variations are disposable supraglottic airway management devices that can be used as an alternative to both mask ventilation and endotracheal intubation in appropriate patients. The LMA also plays an important role in the management of the difficult airway. When inserted appropriately, the LMA lies with its tip resting over the upper esophageal sphincter, cuff sides lying over the pyriform fossae, and cuff upper border resting against the base of the tongue. Such positioning allows for effective ventilation with minimal inflation of the stomach.

  1. Indications
    1. As an alternative to mask ventilation or endotracheal intubation for airway management. The LMA is not a replacement for endotracheal intubation when endotracheal intubation is indicated.
    2. In the management of a known or unexpected difficult airway.
    3. In airway management during the resuscitation of an unconscious patient.
  2. Contraindications
    1. Patients at risk of aspiration of gastric contents, such as patients with a full stomach, or symptomatic gastroesophageal reflux disease.
    2. Patients with decreased respiratory system compliance, because the low-pressure seal of the LMA cuff will leak at high inspiratory pressures, and gastric insufflation may occur. Peak inspiratory pressures should be maintained at less than 20 cm H2O to minimize cuff leaks and gastric insufflation.
    3. Patients in whom long-term mechanical ventilatory support is anticipated or required.
    4. Patients with intact upper airway reflexes, because insertion can precipitate laryngospasm.
  3. Use
    1. LMAs are available in a variety of pediatric and adult sizes (see Table 14.1). Using the proper size maximizes the probability of appropriate cuff fit. Maneuvers for appropriate insertion of the LMA are shown in Figure 14.2.
    2. Ensure correct cuff deflation and lubrication. Lubrication of the LMA inner surface should be avoided because any lubricant dripping into the larynx can precipitate laryngospasm.
    3. Follow usual preoxygenation and monitoring requirements.
    4. Ensure an adequate level of anesthesia and suppression of upper airway reflexes.
    5. Position the patient's head appropriately. The “sniffing” position (slight flexion of the lower cervical spine with extension of C1-2) used to optimize endotracheal intubation also typically provides the best positioning for LMA insertion.
    6. Insert the LMA (see Fig. 14.2). A soft bite block can be used to protect against a patient biting down on the LMA tube.
    7. Inflate cuff (see Table 14.1). Typically, one sees a smooth ovoid expansion of the tissues above the thyroid cartilage with adequate inflation of the appropriately positioned LMA.
    8. Ensure adequate ventilation.
    9. Connect to anesthetic circuit. The LMA can be secured with tape, if necessary.
    10. LMA removal. The LMA generally is well tolerated by a patient emerging from general anesthesia as long as the cuff is not overinflated (cuff pressure less than 60 cm H2O). The LMA can be removed by deflating the cuff once the patient has emerged from general anesthesia and has return of upper airway reflexes.
    11. The LMA is a suitable airway for some patients having procedures in the prone position. If this technique is chosen, patients can position themselves on the operating table before induction. After induction of anesthesia, the LMA can be inserted with the patient's head turned to the side and resting on a pillow or blankets.
  4. Intubating LMAs. There are multiple brands and styles of LMA's that are designed to facilitate intubation of the patient by passing an ETT through them, either blindly or with flexible fiberoptic guidance. The disposable single use air-Q LMA is similar in style to a standard LMA, but has a larger reinforced tube, and removable airway connector that allows the placement of any standard ETT that has been lubricated with water gel lubricant. The reusable LMA Fastrach includes a curved stainless steel tube covered with silicone, a 15-mm end connector, cuff, and an epiglottic lifting bar (Fig. 14.3). The tube is of sufficient diameter to accept a cuffed 8-mm ID ETT and is short enough to ensure that the ETT cuff will rest beyond the vocal cords.
  5. Adverse effects. The most common adverse effect of using any LMA is a sore throat, with an estimated incidence of 10%, and is most often related to over inflation of the LMA cuff. The primary major adverse effect is aspiration, which has been estimated to occur at a comparable incidence as with mask or endotracheal anesthesia.

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