Devices for difficult airway management in adults for emergency medicine and critical care

INTRODUCTION — Emergency clinicians commonly encounter difficult airways. Estimates run as high as 20 percent for difficult airways [1] and approximately one percent for failed airways [2]. Difficulty in airway management is variably defined, and includes the need for excess lifting force, poor view of the vocal cords, multiple or prolonged attempts, multiple operators, and the use of multiple intubating devices.

A wide range of devices have been developed to aid in the management of the difficult airway. They incorporate a variety of fiberoptic, video, optical, and mechanical technologies to enable the operator to obtain a better view of the larynx and facilitate passage of an endotracheal tube (ETT) into the trachea. These devices are useful for management of the difficult or failed airway and for routine intubation.

This topic review will discuss the types of devices designed to facilitate management of difficult and failed airways. The overall approach to the management of such airways is reviewed elsewhere. (See "Approach to the difficult airway in adults for emergency medicine and critical care" and "Approach to the failed airway in adults for emergency medicine and critical care" and "The difficult pediatric airway for emergency medicine".)

STYLETS: STANDARD AND OPTICAL — We define a stylet as a device loaded within the lumen of an endotracheal tube (ETT) to assist tracheal placement. A standard malleable metal stylet is inserted to lend greater stiffness and shape the ETT, thereby improving control. In contrast, specialized stylets facilitate intubation in situations of poor glottic exposure and, if adapted with advanced optics, can provide a better view of the glottis than is obtained with direct laryngoscopy.

Endotracheal tube introducers (gum elastic bougie) — The endotracheal tube introducer (ETI) is an effective and inexpensive adjunct to difficult airway management that is easy to use. We recommend that an ETI be readily available in every emergency department. The technique for using these devices and evidence of their effectiveness are reviewed separately. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

Optical stylets — Optical stylets (OS) incorporate a fiberoptic or video viewing element into the distal end of a metal stylet. The stylet can be rigid, semirigid, or directable. The viewing element effectively moves the intubator's view from outside the mouth with direct laryngoscopy to the region just proximal to the glottis with an OS. The OS may be useful in some patients with a difficult airway. In the absence of obstructing debris, the OS can provide an improved view of the vocal cords and ensure passage of the ETT into the trachea under direct visualization. Use of an OS may reduce cervical spine motion during intubation. Like any nontraditional method of laryngoscopy, the OS requires skill acquisition and maintenance to be used effectively. To date, no clinical trials of OS devices for the management of difficult airways in the emergency department have been performed.

The OS, although more expensive than a lighted stylet, is typically less expensive than other video and fiberoptic laryngoscopes. OS devices have either an eyepiece for viewing the glottis individually or a screen for ease of use, teaching, or supervision. Several of these devices also have a side port to insufflate oxygen in order to prevent secretions from obscuring the fiberoptic tip of the stylet. Common examples of the OS include the Clarus Video System (picture 1), Shikani Optical Stylet (picture 2), Bonfils Retromolar Intubation Fiberscope (picture 3), and the Levitan FPS Scope (picture 4).

Use of OS devices for airway management and supporting evidence are discussed in detail separately. Intubation technique using an OS is described briefly below. (See "Video laryngoscopes and optical stylets for airway management for anesthesia in adults", section on 'Optical stylets'.)

Intubation using an OS involves one of two distinct techniques. In the first, the clinician holds the OS in their right hand while grasping the tongue and mandible with their left and lifting them anteriorly to create space in the posterior pharynx. The clinician then advances the OS into the oropharynx and around the base of the tongue under direct visualization. Once the OS is in position, the clinician uses the eyepiece to identify and enter the larynx.

In the second technique, a laryngoscope blade is used to displace the pharyngeal soft tissues and visualize as much of the larynx as possible. The clinician uses their right hand to advance the OS into the oropharynx under direct visualization, just like a standard ETT. Once the tip of the OS is out of view around the base of the tongue, the clinician uses the OS eyepiece to visualize the larynx and advance the ETT the last few centimeters through the vocal cords. Often, the last few centimeters proximal to the larynx present the greatest challenge to blade laryngoscopy. By using the OS to “see around the corner” and identify the larynx, this step becomes easier. The remainder of both techniques is similar to direct laryngoscopy.

Flexible endoscope

Characteristics — The flexible endoscope (FE) is essentially a 60 cm long flexible and directable stylet that can be used for airway management in patients for whom difficult intubation is predicted and neuromuscular paralysis is best avoided (figure 1). Because of the time required and the patient preparation necessary, intubation using a FE is generally not performed in patients who require immediate establishment of an airway. If time allows for adequate patient preparation, the FE is an invaluable intubating device. FE for intubation is reviewed in detail separately. (See "Flexible scope intubation for anesthesia".)

Among the devices used for difficult airway management, the FE has a unique set of characteristics:

●The FE can be used for either orotracheal or nasotracheal intubation. Nasotracheal use allows access to the vocal cords when oral access is limited.

●The FE can be used with adjunctive devices, such as specially designed oral airways, that improve intubation success.

●More time is required to perform intubation using the FE. Patients must be cooperative (usually achieved by using sedation or dissociation and topical anesthesia), breathing spontaneously, and adequately oxygenated.

●Clinicians must practice longer and more often to acquire and maintain facility with the FE compared with other airway devices.

●The cost of purchasing and maintaining a FE is higher than for most other devices.

Despite these limitations to FE use for emergency airway management, a survey in 1999 found that 64 percent of academic emergency departments had an FE [3].

FEs typically cost thousands of dollars (United States) and can be fragile and difficult to maintain in an emergency department environment. Several single-use, disposable FEs are available. With these devices, the disposable FE connects to a reusable video screen, often one already in use for VL. They come in varying diameters to accommodate a wide range of ETTs.

Clinical use — Indications for FE use include a difficult airway due to limited mouth opening, oral obstructions from infection, hematoma, or angioedema, and upper airway anatomic abnormalities from masses, operations, trauma, or head and neck contractures.

Relative contraindications include copious secretions or blood and a rapidly worsening supraglottic obstruction, such as a foreign body, with imminent airway compromise.

Nasotracheal intubation with the FE offers some advantages, but some clinicians find it more difficult to perform than its oral counterpart because of the greater distances and angles to be negotiated. However, some clinicians prefer the nasotracheal route because the nasopharynx keeps the ETT and FE in the midline, which can be challenging when intubation is performed orally. The nasal route is often better tolerated by the patient and eliminates the risk of the patient biting and damaging the FE. Passage of the FE and ETT through the nasopharynx can cause bleeding, which obscures visualization. Therefore, application of a vasoconstrictor (eg, oxymetazoline, phenylephrine, cocaine) and dilating device (eg, nasopharyngeal airway) prior to the procedure is important to minimize this risk.

We recommend that the intubator insert the well-lubricated ETT first, passing it through the naris and into the nasopharynx, and then insert the FE through the lumen of the tube. This eliminates the possibility that the operator will be unable to successfully pass the ETT into and through the naris after the vocal cords are traversed by the FE. In addition, pre-loading the ETT into the nose provides a clean, smooth pathway for the FE to pass, making contamination with mucous and topical anesthetics less likely and passage easier. The ETT should only be pre-loaded just to the posterior nasopharynx, around the bend, so the tip faces inferiorly at the level of the uvula. This increases the likelihood of obtaining an excellent view of the glottis when the FE emerges from the ETT.

A common pitfall is positioning the ETT too deep, which can impair visualization of the glottis, as the tip of the ETT may be at or below the level of the glottis, typically in a piriform sinus. If airway landmarks are lost, pull the FE back to the tip of the ETT, and then gradually withdraw the ETT and FE together until the glottis, tongue, or uvula is visualized, and then reattempt FE advancement.

If orotracheal intubation is desired, bite blocks are necessary to prevent the patient from biting the FE. Specialized intubating pharyngeal airways (eg, Berman Breakaway Airway, Williams Airway, Ovassapian Airway (picture 5)) designed for use with the FE and shaped to direct the tip of the scope towards the glottis are available. FEs can also be placed through an extraglottic device (eg, laryngeal mask airway) to facilitate endotracheal intubation [4-7]. (See "Flexible bronchoscopy in adults: Indications and contraindications".)

Studies have shown that about 1 percent of all emergency department intubations are performed using a FE, and emergency clinicians performing FE intubations have a success rate between 56 and 99 percent, mostly depending upon the operator's level of experience [8-14].

Technical performance — While a complete tutorial of flexible endoscopes is beyond the scope of this review, there are a few technical points worth highlighting:

●Recognize that the procedure often requires 5 to 20 minutes. If the patient cannot tolerate such a delay, the technique should not be used.

●Stay in the anatomic midline at all times during the procedure. Straying laterally often results in poor visualization and inability to pass the FE through the vocal cords.

●The operator should keep the FE taut between both hands. If slack is present, rotation of the body of the FE will not translate into rotation of the tip.

●In many of the smaller scopes used for intubation, suction through the working channel is ineffective at clearing the field of view.

●Intermittent insufflation of oxygen through the working channel can be useful to clear debris from the scope tip. However, prolonged insufflation can result in barotrauma [15].

●If there is difficulty passing the ETT down the FE and into the trachea, the ETT tip is likely caught at the level of the arytenoids. Counter-clockwise rotation of the entire ETT-FE apparatus will likely overcome the obstruction. Alternatively, a Parker Flex-tip ETT can be used to prevent the gap between the ETT and the FE, thereby reducing the likelihood of the ETT getting caught on the arytenoids and aryepiglottic folds.

EXTRAGLOTTIC DEVICES — Extraglottic airway devices are used to establish an airway for oxygenation and ventilation without entering the trachea. They are important tools for airway management and are used frequently in the prehospital environment, emergency department, operating room, and other settings. They can be primary airway devices, such as during cardiopulmonary resuscitation, or rescue devices for failed airways. Common categories of extraglottic airway devices include supraglottic airways (eg, laryngeal mask airways) and retroglottic airways (eg, laryngeal tubes). A detailed review of the extraglottic airways commonly used for emergency airway management, including text and video clips demonstrating proper placement and use, is found separately. (See "Extraglottic devices for emergency airway management in adults".)

ADVANCED LARYNGOSCOPES

Video laryngoscopes

Types of devices and basic concepts — Video laryngoscopes (VLs) are rigid devices that allow indirect laryngoscopy, or visualization of the vocal cords and related airway structures without a direct line of sight. VLs are fundamentally retraction devices with built-in illumination and optical elements. Over the past few decades, use of VLs has expanded to the operating theater, emergency department, and prehospital setting. A number of different VLs are available, but these can be categorized according to common features, such as blade shape. The use and evidence about VLs for emergency airway management are discussed below; the different types of VLs, details about performance, and use of VLs in the operating theater are all reviewed separately. (See "Video laryngoscopes and optical stylets for airway management for anesthesia in adults".)

VLs vary in important ways by design and adjunct features, such as size, the acuity of the blade curve (standard geometry or hyperangulated), and whether a channel to guide tracheal tube placement is incorporated. As such, any assessment of trials of VL performance should pay specific attention to the type of video device used. Results of studies should not simply be combined without distinction under the label of "video laryngoscope." (See 'Evidence about video laryngoscopes in emergency settings' below.)

VLs use fiberoptics or a micro video camera encased in a laryngoscope to provide a wide-angle view of the glottis. The optics are set back from the tip of the laryngoscope blade, minimizing interference from secretions. Devices with micro video cameras are less expensive and more durable than flexible fiberoptics, which use glass fiber. Examples of VLs include the GlideScope and GlideScope Ranger (picture 6 and picture 7), Pentax Airway Scope (picture 8), McGrath Video Laryngoscope (picture 9), and the Storz CMAC video laryngoscope (picture 10). Few studies have directly compared the performance of one video laryngoscope to another. One retrospective study of 463 intubations performed in the emergency department reported similar rates of first-pass and overall intubation success with the GlideScope and the CMAC [16].

VLs are easy to use and build upon basic direct laryngoscopy (DL) techniques, although some training and adjustments in technique are needed. Furthermore, unlike DL, VL provides the supervisor and trainee with an identical view of the glottis, allowing for improved teaching and troubleshooting.

Video laryngoscopy technique — The use of VLs varies depending upon the configuration of the blade. Most often, the blade is inserted midline, and no tongue sweep is required. With hyperangulated blades, once fully inserted with the blade tip at the base of the tongue in or near the vallecula, the device is tilted slightly, rather than lifted, so that the tip of the blade is oriented directly towards the epiglottis. No lifting force is applied since the curve of the blade corresponds to the shape of the airway. The endotracheal tube (ETT) stylet requires a 70- to 90-degree bend just proximal to the cuff in order to follow the shape of the blade into the glottis. In a randomized trial of surgical patients intubated using the GlideScope, a 90-degree angle improved the ease of intubation, but neither forward nor reverse orientation of ETT camber affected performance [17].

Once the ETT is seen entering the vocal cords, the stylet needs to be partially withdrawn to allow the ETT to bend posteriorly and advance down the trachea. This step can sometimes be challenging. Some manufacturers provide a hyperangulated, reusable, rigid stylet to make it easier for the ETT to reach the larynx. According to a retrospective study of 473 emergency department intubations, use of the rigid stylet is associated with higher rates of successful intubation, both at the first attempt and overall [18]. However, this is in contrast to an operating room report in which the GlideScope proprietary stylet and a standard malleable stylet were found to be equally effective when used by experienced anesthesiologists [19]. Other manufacturers also make hyperangulated stylets that have a steerable tip to allow the ETT to bend anteriorly to reach the larynx, then bend posteriorly to pass down the trachea. Further research is needed to address the question of most effective stylet use.

Further details of VL technique are reviewed separately. (See "Video laryngoscopes and optical stylets for airway management for anesthesia in adults", section on 'Videolaryngoscopy technique'.)

Evidence about video laryngoscopes in emergency settings — VL devices are highly effective and help emergency airway managers maximize first-pass intubation success with both routine and difficult airways. Evidence supporting the use of VL devices in emergency and critical care settings is reviewed separately. (See "Overview of advanced airway management in adults for emergency medicine and critical care", section on 'Choice of laryngoscopy technique'.)

Optical laryngoscopes — Optical laryngoscopes use lenses to provide a view of the larynx similar to VL. Although image quality is inferior to that of VL, optical laryngoscopes are inexpensive, durable, and highly portable. Two examples are the Truview laryngoscope (picture 11 and picture 12) and the Airtraq optical laryngoscope (picture 13).

The Truview EVO has an angled laryngoscope blade with an affixed eyepiece and oxygen insufflation port to keep the optical lens clear of secretions or blood. The eyepiece and lens assembly allows the intubator to see 42 degrees anterior to the axis of the blade, enabling visualization of the glottis with less lifting force and improved exposure compared with a Macintosh laryngoscope [20,21].

The Airtraq is a unique optical laryngoscope with an L-shape, similar to the blade of the Pentax AWS that allows glottic visualization with the head and neck in a neutral position. The SP version is a single-use device, simply constructed, inexpensive, and disposable. The Avant version has a reusable optical channel and disposable single-use blades. Airtraq makes a wi-fi camera that fits all models and provides a screen, wireless video output to PCs and mobile devices, and video recording.

A meta-analysis of 12 small randomized trials involving 1061 patients that compared the Airtraq to a standard Macintosh laryngoscope found that the Airtraq reduced the time required for intubation (-15 seconds, 95% CI -25- -4), increased first pass intubation success rates among novice airway managers (relative risk [RR] 1.25, 95% CI 1.05-1.49), and reduced the incidence of esophageal intubation (RR 0.12, 95% CI 0.03-0.48) [22]. Individual studies noted that use of the Airtraq led to reduced cervical spine motion and less change in heart rate compared with DL using a Macintosh laryngoscope [23-27].

The Airtraq has been used as a rescue device for difficult airways and in one small randomized controlled trial outperformed DL using a Macintosh laryngoscope in patients with preoperatively defined difficult airway features [28].

SURGICAL AIRWAY DEVICES — In emergency medicine, a surgical airway generally involves performing a cricothyrotomy in order to place a cuffed ETT in the trachea. This is most often accomplished using either an "open" or a percutaneous technique. Cricothyrotomy is discussed separately. (See "Emergency cricothyrotomy (cricothyroidotomy) in adults".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Airway management in adults".)

SUMMARY AND RECOMMENDATIONS

●Emergency use of extraglottic devices – Extraglottic devices establish an airway for oxygenation and ventilation without traversing the glottis, and are critical tools for the management of difficult and failed airways. We recommend that clinicians responsible for airway management be familiar with at least one such device and, for emergency use, ideally one that can be used as a conduit to pass an endotracheal tube (ETT) and establish a definitive airway with a high success rate. (See "Extraglottic devices for emergency airway management in adults".)

●Tracheal tube introducer (“bougie”) – The endotracheal tube introducer (ie, ETI or “gum elastic bougie”) is an effective, inexpensive, easy-to-use adjunct to difficult airway management. We recommend that these be available in every emergency department. (See "Endotracheal tube introducers (gum elastic bougie) for emergency intubation".)

●Optical stylets – Optical stylets (OS) incorporate a fiberoptic or video viewing element into the distal end of a metal stylet. The stylet can be rigid, semirigid, or directable. The viewing element effectively moves the intubator's view from outside the mouth to the tip of the OS and closer to the glottis, making it useful in patients with a difficult airway. (See 'Optical stylets' above.)

●Flexible endoscope – The flexible endoscope (FE) is essentially a flexible and directable stylet that can be used for airway management when difficult intubation is predicted, time is available, and neuromuscular paralysis is best avoided. Intubation using a FE is generally not performed in patients who require immediate establishment of an airway. (See 'Flexible endoscope' above.)

●Video and optical laryngoscopes – These are highly effective tools that can help maximize first-pass intubation success in both routine and difficult airway scenarios. Video laryngoscopes provide superior views of the glottis compared with direct laryngoscopy, cause minimal movement of the cervical spine, and are preferred for emergency intubation. (See 'Video laryngoscopes' above and "Video laryngoscopes and optical stylets for airway management for anesthesia in adults".)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Aaron E Bair, MD, MSc, FAAEM, FACEP, now deceased, who contributed to an earlier version of this topic review.