Extraglottic Devices: Supraglottic Type

INTRODUCTION AND TERMINOLOGY

The terminology related to airway management devices that are inserted into the hypopharynx and upper esophagus is not standardized. We will employ the term extraglottic devices (EGDs) to refer to this collection of devices. Those that sit on top of the larynx are supraglottic devices (SGDs), and those that are blindly inserted into the upper esophagus are retroglottic devices (RGDs). This latter group might also be referred to as an infraglottic devices (IGDs). RGDs such as the Combitube, King LT airway, and EasyTube are covered in the following chapter. Most EGDs are single-use, but some are available in reusable variants.

EGDs differ from face mask gas delivery apparatus in that they are inserted through the mouth to a position where they provide a direct conduit for air to flow through the glottis and into the lungs. They vary in size and shape, and most have balloons or cuffs that, when inflated, provide a reasonably tight seal in the upper airway to permit positive-pressure ventilation with variable limits of peak airway pressure. This chapter deals with SGDs such as the LMA family of devices, Cook ILA and Air Q, Ambu Aura family, and the i-gel.

The SGD Class is further divided into first generation (no gastric drainage lumen) and second generation (possessing a gastric drainage tube).

INDICATIONS FOR USE

Although bag-mask ventilation (BMV) is relatively simple in concept, it is difficult or impossible to perform in selected patients (see Chapter 9), even in the hands of experts. Use of an EGD is a more easily acquired skill than BMV for the nonexpert airway practitioner. Similarly, tracheal intubation is the “gold standard” for effective ventilation and airway protection from aspiration, but the skill is not easily mastered or maintained. EGDs are a viable alternative to tracheal intubation in many emergency settings, particularly in prehospital care.

Finally, airway management difficulty and failure are associated with significant morbidity and mortality. EGDs have a potential role in managing or rescuing both the difficult and failed airway (see Chapters 2 and 3).

The indications for these devices have expanded over the past three decades and include potential for use as:

• An airway rescue device when BMV is difficult and intubation has failed;

• A “single attempt” rescue device performed simultaneously with preparation for cricothyrotomy in the “can’t intubate, can’t oxygenate” (CICO) failed airway (see Chapter 3);

• An easier and more effective alternative to BMV in the hands of basic life support providers or nonmedical rescue personnel;

• An alternative to endotracheal intubation by advanced life support providers;

• An alternative to endotracheal intubation for elective airway management in the operating room (OR) for appropriately selected patients; and

• A conduit to facilitate endotracheal intubation (certain types of intubating SGDs).

SUPRAGLOTTIC DEVICES

The Laryngeal Mask Company developed the original SGD, the LMA Classic (Fig. 10-1), which serves as the prototype for much of the supraglottic class, although other designs exist. The company also makes several other versions of the LMA, including both reusable and nonreusable (disposable) devices as follows:

• LMA Unique (disposable variant of the LMA Classic)

• LMA Flexible (reinforced tube variant of the LMA Classic)

• LMA ProSeal (reusable) (Fig. 10-2)

• LMA Supreme (disposable) (Fig. 10-3)

• Fastrach or intubating LMA (ILMA) (reusable and disposable) (Fig. 10-4)

Other companies also make SGDs, both LMA type and non-LMA type, including

• A variety of disposable LMA Classic type designs (e.g., Portex and Solus);

• Ambu LMA (ALMA) family of devices (AuraOnce, Aura Straight, Aura-i; disposable and reusable) (Fig. 10-5);

• Cookgas ILA (reusable) and Air Q (disposable) (Fig. 10-6A and B); and

• i-gel (Fig. 10-7).

• FIGURE 10-1. LMA Classic. Note the aperture bars at the end of the plastic tube intended to limit the ability of the epiglottis to herniate into this opening.

• FIGURE 10-2. LMA ProSeal. Note the drain tube and distal orifice to permit gastric tube passage and drainage.

• FIGURE 10-3. LMA Supreme. The rigid construction of the tube and the curvature of the device enhance insertion characteristics and the immediacy of the seal obtained once inflated.

• FIGURE 10-4. LMA Fastrach or ILMA. Both the reusable (bottom) and disposable (top) variants are pictured. The most unique feature of this device that confers a particular advantage is the handle to permit positioning in the hypopharynx to improve airway seal and the capacity for adequate gas exchange. This factor may be crucial in rescuing a failed airway.

• FIGURE 10-5. A: Range of sizes of the Ambu AuraOnce LMA. B: Ambu Aura-i LMA, specifically designed to be used with the Ambu A Scope for endoscopic intubation.

The LMA Company (now owned by Teleflex) has recently introduced two new single-use devices that have novel features: The LMA Protector (Fig. 10-8) is a second-generation silicone single-use device that is available with both a gastric drainage tube and a vent (second-generation SGA) that incorporates Cuff Pilot technology, a pilot balloon pressure indicator. The device bears similarity to the LMA Supreme, but is easier to intubate through. It is also similar in feel and shape to the Fastrach LMA, although it lacks the handle and endotracheal tube ramp.

The single-use Unique EVO (Fig. 10-9) is a successor to the LMA Unique, with a couple of design modifications: a more robust cuff design meant to produce better seal characteristics and Cuff Pilot technology.

These devices are easy to use, generally well tolerated, produce little in the way of adverse hemodynamic responses on insertion, and play a significant role in rescue emergency airway management. Ventilation success rates near 100% have been reported in OR series, although patients with difficult airways were excluded. It is likely that emergency airway ventilation success rates are somewhat lower. Intubation success rates through the ILMA are as high as 95% after three attempts, comparable to success rates with flexible endoscopic intubation and significantly better than through the standard LMA (See evidence section). However, an LMA does not constitute definitive airway management, defined as a protected airway (i.e., a cuffed endotracheal tube [ETT] in the trachea). Although they do not reliably prevent the gastric insufflation or the regurgitation and aspiration of gastric contents, LMAs confer some protection of the airway from aspiration of blood and saliva from the mouth and pharynx.

• FIGURE 10-6. A: The reusable Cookgas ILA. B: The disposable Air Q variant.

• FIGURE 10-7. The i-gel Device. Note the esophageal drainage tube.

• FIGURE 10-8. Correct method of deflating the LMA Cuff.

• FIGURE 10-9. Correct position of the fingers for LMA Insertion.

Maximal success is only achievable when the patient has effective topical airway anesthesia (see Chapter 23) or is significantly obtunded (e.g., by rapid sequence intubation medications) to tolerate insertion of these devices.

LARYNGEAL MASK COMPANY DEVICES

Standard, Non-ILMAs

The original LMA, now called the LMA Classic, was introduced into clinical practice in 1981 and looks like an ETT equipped with an inflatable, elliptical, silicone rubber collar (laryngeal mask) at the distal end (Fig. 10-1). The laryngeal mask component is designed to surround and cover the supraglottic area, providing upper airway continuity. Two rubber bars cross the tube opening at the mask end to prevent herniation of the epiglottis into the tube portion of the LMA.

The LMA Classic is a multiuse (reusable) device. The disposable and much less expensive variety of this device is called the LMA Unique. A similar product, the LMA Flexible, incorporates wire reinforcement in the tube portion of the device to prevent kinking as the tube warms. We do not recommend the LMA Flexible for management of the emergency airway.

The reusable LMA ProSeal incorporates an additional lumen through which one can pass a suction catheter into the esophagus or stomach. In addition to the standard perilaryngeal cuff, it also has a “directional sealing cuff” dorsally. This design modification results in higher sealing pressure capacity than the LMA Classic (28 vs. 24 cm H₂O), theoretically conferring an advantage for ventilating patients requiring higher airway pressures, although the difference may not be clinically significant. Because of its expense, relative difficulty with insertion characteristics, and marginal benefit in the emergency situation, the LMA ProSeal does not currently have a place in emergency airway management.

A disposable device similar to the LMA Classic called the LMA Supreme has compelling design characteristics that may make it a good rescue device for emergency airway management. It is easy to insert, seals readily, has higher leak pressures than do earlier LMA iterations, has a built-in bite block, and contains a channel through which a gastric tube can be passed. This device can be considered as a replacement for BMV in the hands of nonexpert airway managers or when rescue BMV is expected to be prolonged. It is the preferred device for emergency airway management if a nonintubating style of LMA is desired.

Intubating LMAs

The LMA Fastrach, also called the ILMA, is the most important version of the LMA for emergency airway management because it combines the high insertion and ventilation success rate of the other LMAs with specially designed features to facilitate blind intubation. It has an epiglottic elevating bar and a rigid guide channel that directs an ETT in a superior direction into the larynx, enhancing the success rate when passed blindly. The LMA Fastrach device is a substantial advancement in airway management, particularly as a rapidly inserted rescue device in the CICO situation while preparations for cricothyrotomy are underway. It is supplied in both reusable and disposable forms.

Indications and Contraindications

The LMA and LMA Fastrach have two principal roles in rescue emergency airway management: (1) as a rescue device in a “can’t intubate, can oxygenate” situation, and (2) as a single attempt to effect gas exchange in the CICO failed airway as one concurrently prepares to perform a cricothyrotomy (see Chapter 3). The success rate of LMA-facilitated ventilation in the difficult airway may be eroded if multiple preceding intubation attempts have traumatized the upper airway.

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