Laryngeal Mask Airway

LMAs are 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 piriform fossae, and cuff upper border resting against the base of the tongue (see Figure 13.4). 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.
      

      Figure 13.4 Position of properly inserted laryngeal mask airway.

      (Reproduced with permission from Doyle DJ. Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults. In: Post TW, ed. UpToDate. UpToDate. Accessed May 12, 2020. Copyright © 2020 UpToDate, Inc. For more information visit www.uptodate.com.)

   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. The low-pressure seal of the LMA cuff will leak at high inspiratory pressures resulting in gas entering the esophagus and gastric insufflation. Peak inspiratory pressures should be maintained at less than 20 cmH₂O 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 13.2). Using the proper size maximizes the probability of appropriate cuff fit. There are many techniques for inserting the LMA. A common maneuver for insertion of the LMA is shown in Figure 13.5. Alternatively, the cuff can be inserted partially inflated at a 90-degree angle to its final position. It is pinched as it passes between the tongue and hard palate and rotated into position while advancing until definite resistance is felt at the base of the hypopharynx.
      

      Figure 13.5 Technique for Insertion of LMA.

      Top left:Grasp the airway tube in the dominant hand and place the index finger between the tube and the deflated cuff of the mask.

      Top right:With the nondominant hand adjusting the head into the “sniffing” position, place the tip of the mask firmly against the palate and advance the LMA along the palate and into the posterior pharynx with the initial direction of force directed toward the operator’s umbilicus.

      Lower left:The nondominant hand is then used to push the LMA further into the hypopharynx until resistance is encountered at the UES.

      Lower right:Once inserted, the cuff of the LMA is insufflated with just enough air to create a seal.

      (From Egan B. Supraglottic airway devices. In: Chu LF, Traynor AJ, Kurup V, edsManual of Clinical Anesthesiology. 2nd ed. Philadelphia, PA: Wolters Kluwer; 2021:190-199 and adapted from Walls RM, Murphy MF. Manual of Emergency Airway Management. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2008:125-127.)

   2. The outer surface of the cuff may be lubricated to aid insertion. Lubrication of the LMA inner surface should be avoided because 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 Figure 13.5). A soft bite block can be used to protect against a patient biting down on the LMA tube.
   7. Inflate cuff (see Table 13.2). 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 with chest rise, end-tidal CO₂.
   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 cmH₂O). 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 may be 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. Second-generation LMAs. Classic LMAs consist of a cuff, valve, airway tube, and circuit connection. “Second-generation” LMAs have additional functionality for unique situations and many include a widened proximal tube, which functions as a built-in bite-block.
   1. Intubating LMAs are designed to facilitate intubation of the patient by passing an ETT through them, either blindly or with flexible bronchoscopic guidance.
   2. 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 (up to 8.5-mm ID) that has been lubricated with water gel lubricant.
   3. The reusable LMA Fastrach includes a curved stainless-steel tube covered with silicone, a 15-mm end connector, cuff, and an epiglottic lifting bar (Figure 13.6). 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.
      

      Figure 13.6 Features of the laryngeal mask airway fastrach.

      (Image courtesy of Teleflex Incorporated. Copyright © 2021 Teleflex Incorporated. All rights reserved.)

   4. Flexible-reinforced LMAs have small, wire-reinforced airway tubes, which allow significant manipulation of the airway tube without interference with mask seal. These are particularly useful in procedures involving the head and neck where a classic LMA could obstruct the surgical field.
   5. The LMA ProSeal incorporates a high-pressure cuff and conduit for an orogastric tube for use in situations where risk of aspiration is elevated and has been employed successfully in laparoscopic surgery.
   6. The LMA Gastro incorporates a large channel to allow passage of an endoscope.
5. Adverse effects. The most common adverse effect of using an LMA is a sore throat with an estimated incidence of 10%. The primary major adverse event is aspiration, which occurs at an incidence comparable to mask or endotracheal anesthesia. LMAs have been associated with lingual, recurrent laryngeal, and hypoglossal nerve injuries. LMA use for a duration greater than 3 hours should be avoided.