Video laryngoscopes and optical stylets for airway management for anesthesia in adults

INTRODUCTION — Video laryngoscopes (VLs) and optical stylets (OS) 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 illumination and optical elements. By contrast, OS provide little retraction. They are tubular devices that fit inside the tracheal tube and convey an image using either a fiberoptic bundle or a video camera.

Optical indirect laryngoscopes use prisms, lenses, and mirrors rather than electronic components. The only available example of such a device is the Airtraq, which for the sake of simplicity we will consider a VL.

This topic will discuss the various types of VLs and OS, the techniques used for endotracheal intubation with these devices in adults, and airway management outcomes with their use. Direct laryngoscopy, flexible scope intubation, use of supraglottic airways in anesthesia, and videolaryngoscopy in children, are discussed separately. (See "Direct laryngoscopy and endotracheal intubation in adults" and "Flexible scope intubation for anesthesia" and "Supraglottic devices (including laryngeal mask airways) for airway management for anesthesia in adults" and "Video laryngoscopy and other devices for difficult endotracheal intubation in children", section on 'Video laryngoscope'.)

ADVANTAGES OF VIDEO LARYNGOSCOPES AND OPTICAL STYLETS — The primary advantage of indirect laryngoscopy devices is the ability to look around corners, enabling the operator to see what is not within the line of sight, using fiberoptic bundles, video cameras, or prisms. Other advantages include the option for other clinicians to simultaneously see what the operator sees, which creates opportunity for collaboration and teaching, and the fact that almost all of these devices enlarge the image. Some devices allow for recording, which is useful for clinical documentation, quality improvement, and teaching. They also create an opportunity for remote supervision by a more experienced airway manager, which may be beneficial in under-resourced hospitals and during prehospital emergency airway management [1].

Videolaryngoscopy may reduce cervical spine motion, compared with direct laryngoscopy, especially when used with manual in line stabilization. (See "Anesthesia for adults with acute spinal cord injury", section on 'Choice of airway device'.)

Laryngoscopy with some video laryngoscopes (VLs) creates reduced lifting force on the base of the tongue, compared with the Macintosh laryngoscope, and might theoretically attenuate the stress response to laryngoscopy and intubation [2,3]. However, studies have failed to show a reduction in the hemodynamic response to intubation with the use of rigid VLs [4-8].

VIDEOLARYNGOSCOPY

Classification of video laryngoscopes — Video laryngoscopes (VLs) can be categorized according to the shape of the blade (Macintosh style versus acute-angle) and whether or not they have channels that accommodate and guide tracheal tube advancement [9-12]. Nonacute angle VL blades are sometimes called conventional blades. Miller style blades are available in pediatric sizes.

Non-channeled VL — For endotracheal intubation with a VL without a channel, the device is used to obtain a view of the larynx, and the endotracheal tube (ETT) is passed through the vocal cords independent of the device. Non-channeled VLs can be divided into those with conventionally curved blades similar to the Macintosh blade used for direct laryngoscopy (DL) (picture 1), and those with acute-angle blades. A number of manufacturers of VLs make models with both types of blades (picture 2A-B).

The King Vision is available in a non-channeled or channeled version, both of which have an acute-angle blades, shaped to match the anatomic curve of the upper airway (picture 3).

Macintosh-style VL — Macintosh-style VLs can be used for both indirect and direct laryngoscopy. Therefore, they are useful for teaching and supervising DL, since the instructor can see a view on the monitor that is very similar to what the trainee sees while performing DL. Macintosh-style VL blades are available in reusable and single-use formats in the GlideScope and Storz C-MAC systems (picture 4 and picture 2A) and in single-use format for the McGrath MAC (picture 5).

Acute-angle blade VLs — An acute-angle VL blade allows better visualization of anterior laryngeal structures than a more gently curved blade. These devices cannot usually be used for DL. Examples of devices with acute-angle blades include reusable and single-use versions of the GlideScope LoPro and C-MAC D-Blade, and the single-use GlideScope AVL and McGrath MAC X blades (picture 6 and picture 7 and picture 8 and picture 9). The GlideScope blade is oriented upward at a 60-degree angle, with the recessed wide-angle CMOS camera located one-third of the way from the distal tip of the blade.

A stylet or tracheal introducer should be used to guide the tip of the ETT into the glottis when using acute-angle VLs. The use of these blades without an introducer is contrary to the manufacturers' recommendations and may require repeated attempts at laryngoscopy [13]. Specialized rigid stylets are available for use with GlideScope (picture 10) and C-MAC acute-angle blades.

Channeled VL — Channeled VLs are shaped to match the anatomic curve of the upper airway. All are designed to be positioned around the base of the tongue, providing laryngeal exposure with reduced cervical manipulation or tongue displacement. They do not allow for independent manipulation of the tracheal tube; rather, the tube is directed by manipulating the laryngoscope itself. Channeled VLs are bulkier than those without channels since they must accommodate an ETT adjacent to the optical and light-emitting diode (LED) elements. Therefore, these devices may not be appropriate for patients with significantly limited mouth opening.

The most widely used channeled VLs are the Airtraq Avant (picture 11 and picture 12 and picture 13), Airway Scope (Pentax) (picture 14), and King Vision (Ambu) (picture 3). All of these laryngoscopes are entirely disposable or have single-use components. The channeled VLs are all similar in shape and concept but differ with respect to the range of available sizes, and the type and quality of display. The King Vision VL is also available with a non-channeled blade.

There are brands of VLs other than those mentioned above, also with a variety of blade shapes.

Pediatric VL options — Most of the forementioned VLs have blade options that include pediatric sizes. Pediatric-sized Miller VL blades are also available in the GlideScope and C-MAC systems. (See "Video laryngoscopy and other devices for difficult endotracheal intubation in children", section on 'Video laryngoscope'.)

Other distinguishing features of VLs — A number of features differ between VLs. Many of these features change regularly with advances in technology [14-16]:

●Blade size availability (eg, pediatric and adult) (see "Video laryngoscopy and other devices for difficult endotracheal intubation in children", section on 'Video laryngoscope')

●Blade thickness, which is particularly important in patients with limited mouth opening

●Availability of reusable and single use versions

●Resolution of the video camera or display

●Monitor size, lighting, resolution, display options, portability, input and output options (image 1)

●Ability to save images and videos (eg, with SD card or USB drive)

●Cost per use

Videolaryngoscopy technique — When using all types of VL, the operator should be looking directly into the patient's mouth, not at the video screen, when inserting the VL into the oropharynx, until the blade tip has been advanced past the soft palate and tonsillar pillars. The same applies to the initial insertion of a styletted ETT, unless using a channeled VL. This is crucial to help avoid injury to intraoral soft tissues. An example of a soft tissue injury as a result of watching the monitor rather than the ETT is shown in a video (movie 1).

Proficiency with the use of VLs requires hands-on instruction, starting with practice on manikins, and followed by laryngoscopy for patients with apparently normal airways.

This section will discuss the techniques for use of representative versions of the many available VLs.

Macintosh-style VL technique — The technique for laryngoscopy and intubation with a C-MAC Macintosh blade VL is described here, as representative of this class of VL, and is shown in a video (movie 2).

●Turn on the monitor and device at least one minute prior to laryngoscopy to minimize condensation on the lens.

●Consider use of a stylet in the ETT, ensuring that the tip does not protrude beyond the ETT. A stylet will increase the likelihood of success on the first attempt, though it may prove to have been unnecessary [13]. Alternatively, a coudé-tipped tracheal introducer [17] or a dynamic stylet (eg, Parker Flex-It Stylet or Truflex articulating stylet) can be used to direct the tracheal tube toward the larynx (picture 15 and picture 16), if needed. Routine use of a stylet or tracheal tube introducer is particularly recommended for the McGrath MAC VL, since its Macintosh blade has slightly more anterior/acute angulation than a typical Macintosh blade.

●Position the patient's head and neck as one would for optimal direct laryngoscopy. (See "Direct laryngoscopy and endotracheal intubation in adults", section on 'Positioning the patient'.)

●Open the patient's mouth as one would for direct laryngoscopy. (See "Direct laryngoscopy and endotracheal intubation in adults", section on 'Opening the mouth and inserting the blade'.)

●Insert the laryngoscope along the right side of the patient's tongue, displacing the tongue to the left, avoiding contact with the lips and teeth. Visualize the airway structures, under direct or indirect vision, centering the blade in the vallecula. This will be aided by identifying the midline, vertically oriented, median glossoepiglottic fold in the vallecula, which should be targeted with the blade tip [18]. Midline placement will help position the blade to engage the underlying hyoepiglottic ligament as the laryngoscope lifted distally, elevating the epiglottis and exposing the underlying glottis. Advance the laryngoscope only as deeply as necessary to place the tip in the vallecula, to avoid downfolding of the epiglottis [19].

●If the direct view is suboptimal, check the indirect view on the monitor as this may offer slightly better laryngeal exposure, permitting intubation on the first attempt. If the view is still suboptimal, apply external laryngeal pressure and/or place your right hand under the patient's head and elevate it off the pillow [20].

●While holding the laryngoscope still, insert the ETT under direct vision along the right side of the mouth until the tip is at the base of the tongue.

●Advance the ETT further, watching the tip of the tube appear on the monitor. Do not advance the ETT if resistance is felt.

●Insert the ETT through the vocal cords and if a stylet has been used, partially or fully withdraw this prior to further advancing the ETT.

Acute-angle blade VL technique — The technique for laryngoscopy using the GlideScope LoPro or AVL blade is described here, as representative of this class of VL.

●Turn on the monitor and device at least one minute prior to laryngoscopy to minimize condensation on the lens.

●Insert a stylet into the ETT, making sure that the tip of the stylet does not protrude beyond the end of the ETT. The manufacturer's dedicated rigid stylet (eg, the GlideRite) can be used, or a standard malleable stylet, manually shaped to a similar angle as the GlideRite within the ETT before use [21].

●Position the head and neck in a neutral or a sniffing position [22].

●Patients with obesity should be placed in the ramped position because it offers a physiologic and mechanical advantage for ventilation (figure 1) (see "Anesthesia for the patient with obesity", section on 'Positioning for airway management'). Insertion of the laryngoscope blade into the patient’s mouth will be easier in the ramped position compared with the neutral position, particularly if augmented by a cross-finger mouth opening maneuver. It is unknown whether the ramped position improves laryngeal visualization when videolaryngoscopy is used.

●Lubricate the VL blade lightly to facilitate passage around the tongue (ensuring that lubricant is not applied near the camera).

●With the patient's mouth opened, insert the blade in the midline, under direct vision until the blade tip is past the soft palate. Rotate the blade in the sagittal plane around the base of the tongue, watching the monitor, and avoid excessively deep insertion. There is no need to advance the blade tip of acute-angle VLs completely into the vallecula, and there are benefits to more shallow insertion.

•Deep insertion of an acute-angle blade rotates the laryngeal axis anteriorly, which may make insertion of the ETT more difficult despite good laryngeal exposure.

•Shallow insertion provides three additional benefits:

-A wider visual field;

-A straighter pathway for ETT delivery from teeth to larynx [23];

-A shorter distance from the lips to the camera, and therefore a shorter blind zone in which the clinician cannot see the tip of the ETT.

●Gently lift the VL upward and forward, in the axis of the laryngoscope handle, to create space beneath the blade.

●Insert the styletted ETT under direct vision, adjacent to the laryngoscope blade, until the tip passes the soft palate. Then direct attention to the monitor, placing the tip of the tube in the midline below the arytenoid cartilages.

●Lift the tip of the tube (vertically) and advance the tip between the vocal cords. Then partially withdraw the stylet and gently advance the ETT into the trachea.

Troubleshooting non-channeled videolaryngoscopy — Although videolaryngoscopy is usually straightforward, problems with insertion of the laryngoscope or the ETT may occur.

●Tip of the ETT not visible – Withdraw the VL until the ETT is visible and then advance both the laryngoscope and ETT.

●Small mouth opening – Insert the tracheal tube before, or concomitantly with, the VL blade [24,25].

●Difficulty directing the ETT to the larynx – A flexible scope or optical stylet (OS) can be used along with the VL to direct the tip of the ETT between the vocal cords [26]. Alternatively, a dynamic stylet (eg, Parker Flex-It Stylet or Truflex articulating stylet) can be used to direct the tracheal tube toward the larynx (picture 15 and picture 16).

●Difficulty advancing the ETT in the trachea – If the ETT is not easily advanced in the trachea once it is inserted between the vocal cords and the stylet has been partially withdrawn, gently rotate the ETT to disengage the tip from the tracheal rings. If this maneuver is unsuccessful, insert a coudé-shaped bougie or flexible scope through the ETT into the trachea, and advance the ETT over it.

●Unsuccessful first attempt – If the first attempt at intubation with a VL fails, subsequent management depends on whether oxygenation and ventilation are possible and should follow difficult airway guidelines (algorithm 1). For patients in whom ventilation is adequate, the following strategy is reasonable:

•Unsuccessful first attempt with Macintosh-style VL – If a poor laryngeal view is obtained when using a Macintosh-style VL, switch to an acute-angle VL or channeled VL (most of which are hyperangulated) to improve glottic exposure.

•Unsuccessful first attempt using hyperangulated blade VL – Failed tracheal intubation can occur despite a good glottic view [27,28]. This can sometimes be addressed by adjusting the curvature of a styletted tracheal tube or tracheal tube introducer for another attempt with the same device [29]. There is also some evidence that deliberately obtaining a more restricted view of the larynx may help [23] to help create a straighter path to the larynx. Defaulting to DL or Macintosh VL may also succeed [30,31] unless already proven to have to have failed.

Channeled VL — The techniques for intubation with the various channeled VLs are slightly different, depending on the device, as noted in this discussion.

●Lubricate the ETT and insert it into the channel, advancing and retracting it to ensure that this can be done smoothly without damaging the cuff. No more than the distal tip of the ETT should be visible in the viewfinder/monitor.

●Turn the device on. The Airtraq LED will flicker for 30 to 60 seconds to indicate the warm-up phase of the lens's heating element. Once heated, this will help prevent fogging.

●Apply a film of a water-soluble lubricant to the lingual surface of the blade to promote smooth advancement over the tongue.

●Open the patient's mouth, and insert the VL in the midline, under direct vision. Once the blade tip is past the soft palate, rotate the blade in the sagittal plane around the base of the tongue, watching the monitor, until the arytenoids are seen.

•Airtraq/Channeled King Vision Scope – Introduce the blade into the proximal vallecula. The larynx may come into view when the laryngoscope is lifted in a vertical plane. If this fails to provide a laryngeal view, lift the epiglottis with the blade. Carefully manipulate the laryngoscope as the ETT is slowly advanced into the trachea. Lateral rotation (often to the left), elevation, or forward (caudad) angulation of the VL may help align the advancing ETT with the larynx (movie 3 and movie 4).

•Ambu/Pentax Airway Scope (AWS) – Prepare the AWS and ETT as for the Airtraq. The single-use blade is bulky and may be difficult to insert in a patient with limited mouth opening. Insert the blade into the mouth and then beneath the epiglottis with the goal of directly elevating it, as with use of a Miller laryngoscope blade. Lift the laryngoscope gently to reveal the larynx and manipulate the laryngoscope and ETT as for the Airtraq to help advance the ETT through the vocal cords and into the trachea.

●Remove the channeled VL carefully. While holding the ETT at a constant depth within the trachea, separate it laterally (to the right) from the VL channel. Once the ETT is disengaged from the channel, while holding it in place, the VL can be rotated back out of the mouth by reversing the trajectory used for its insertion.

For the Airtraq, prior to separating the ETT laterally, deflect the proximal ETT slightly anteriorly to disengage it from the retaining tab (picture 13).

Awake videolaryngoscopy — VLs can be used for awake laryngoscopy and intubation as an alternative to flexible scope intubation [32]. Awake videolaryngoscopy requires experience with the selected device. It is not appropriate for all awake intubations (eg, patients with severely restricted mouth opening or significant head and neck flexion deformity), so awake VL does not reduce the need to maintain skill with flexible scope intubation.

Awake videolaryngoscopy requires the same topical anesthesia and sedation as flexible scope intubation. Indications for awake intubation and patient preparation for the technique are discussed separately. (See "Management of the difficult airway for general anesthesia in adults", section on 'Awake intubation' and "Flexible scope intubation for anesthesia", section on 'Preparation for awake intubation'.)

Intubation success and outcomes with video laryngoscopes — High rates of success are reported for tracheal intubation with VLs. Successful intubation is achieved in >95 percent of patients with normal airways with the use of VLs [27,33,34].

A number of studies have reported that GlideScope intubation may fail despite an excellent view of the larynx [27,28]. The authors of this topic are of the opinion that this reflects limited appreciation of the differences between DL and acute-angle VL [35], and that a good laryngeal view should almost always be followed by intubation success.

VL versus DL — The authors of this topic, some other UpToDate contributors, and some airway guidelines suggest using VL rather than DL for first attempt at intubation when possible [36,37]. Other UpToDate contributors use VL selectively, depending on patient factors and the clinical situation. (See "Airway management for induction of general anesthesia", section on 'Choice of intubation technique'.)

Many studies have reported an improved laryngeal view with the use of VLs in patients with [38] or without predictors of difficult laryngoscopy [39-42]. Intubation success rates with VLs are high, and when used by clinicians experienced in the use of VL, success rates with VLs are similar to [33,43] or higher [34] than success rates for DL. One multicenter randomized operating room trial compared DL with VL using the McGrath Mac (with Mac blade) with Macintosh blade DL and found a significantly higher first pass success rate with the McGrath VL compared with DL (94 versus 82 percent) [44]. The study used anesthesia providers of varying levels of experience, with subgroup analysis revealing that the results persisted for trainees (93 percent first attempt success with VL versus 77 percent for DL). This is one of the largest clinical trials of VL versus DL in the operating room environment to date using first attempt success as the primary outcome. Another large randomized clinical trial of critically ill adults intubated in the emergency department or intensive care unit found a significantly higher first attempt success with VL compared with DL [45]. This study is discussed in detail separately. (See "Overview of advanced airway management in adults for emergency medicine and critical care", section on 'Choice of laryngoscopy technique'.)

Much of the literature on VL has emphasized its value for the less experienced laryngoscopist [33,45]. It seems clear that experience with DL does not necessarily confer expertise with VL. Development of expertise with VL is more complex than was first thought and requires training and practice [46]. Consistent with this result, two studies have reported increased success rates with GlideScope intubation at institutions where it was used more frequently [30,47].

●VL after difficult DL – Importantly, VLs may improve intubation success in patients with difficult or failed DL, and these devices have become part of various difficult airway algorithms [48-51]. Benefits of VLs have been reported in patients with predicted [38,41,52,53], encountered [40], or simulated [54,55] difficult intubation, rapid sequence intubation [56], patients with obesity [57,58], and patients with immobilized cervical spines [59].

●Intubation time – Intubation times reported in studies comparing DL and VL vary widely and are difficult to interpret because of heterogeneity among patient populations, clinical settings, and clinicians. In studies of patients with difficult airways, intubation times with VLs have generally been the same as, or less than, intubation times with DL [60-63].

Comparison of various VLs — Most of the literature comparing VL with DL has included all types of VL blades and devices, thereby limiting conclusions [64]. However, two meta-analyses published in 2022 assessed outcomes with specific types of VLs when compared with DL using Macintosh blades. Whether a specific VL or type of VL is superior to another is unclear.

●A 2022 meta-analysis of 222 randomized or quasi-randomized trials (>26,000 patients) analyzed intubation outcomes with Macintosh-style VLs, acute angle (hyperangulated) VLs, or channeled VLs as individual groups [65]. The overall quality of evidence was moderate to very low for various outcomes, primarily related to lack of blinding in the trials. For outcomes with moderate certainty:

•All types of VLs reduced failed intubation and improved glottic views.

•Macintosh-style and channeled VLs reduced hypoxemic events related to intubation.

•Acute angle VLs reduced esophageal intubation. In a subgroup analysis, acute angle VLs were more likely to reduce failed intubation in patients with predicted or known difficult intubation.

In a sensitivity analysis of all types of VLs combined, VLs reduced failed intubation, hypoxemic events, and esophageal intubation, and very slightly improved the rate of first attempt success.

●A 2022 network meta-analysis of 179 randomized trials compared intubation outcomes with various VLs versus DL with Macintosh laryngoscopes [34]. There were no significant differences between specific types or groups of types of VLs with respect to failed intubation. Altogether, VLs reduced the rate of failed intubation compared with DL, though intubation success was >99 percent with both VLs and DL. The overall quality of data was low to very low.

Predictors of difficult intubation with VL — Difficult and failed videolaryngoscopy does occur, and alternate methods for airway management should always be available. The predictors of difficult intubation with VL are not as well defined, but may overlap with predictors of difficult intubation with direct laryngoscopy (table 1 and table 2). Criteria for designating videolaryngoscopy as difficult are not well-established.

In one review of acute-angle blade VL intubations in 1100 patients with predictors for difficult DL, difficult VL was defined as one requiring more than one attempt or >60 seconds. Predictors of difficult VL included the supine/sniffing rather than supine/neutral position, otolaryngologic or cardiac surgery versus general surgery, small mouth opening, and intubation by an attending rather than a supervised resident [31].

A retrospective review of over 2000 GlideScope intubations reported that abnormal neck anatomy, with the presence of a surgical scar, radiation changes or a mass, were the strongest predictors of failed intubation [30]. Other associated risk factors included thyromental distance <6 cm, limited cervical spine motion, and the institution at which the intubation occurred. In contrast with some other studies, the majority of GlideScope failures were associated with a poor view of the larynx. In 79 percent of the patients with failed GlideScope attempts, intubation was ultimately achieved by direct laryngoscopy or flexible scope intubation.

In another study including 400 elective surgical patients who underwent DL followed by intubation with a GlideScope, high upper lip bite test score (ie, decreased ability to protrude the mandible) and poor laryngeal view with DL (ie, Cormack-Lehane grade 3 or 4) (figure 2) were associated with multiple intubation attempts and longer intubation times with the GlideScope [66]. (See "Airway management for induction of general anesthesia", section on 'Airway examination'.)

Cost of videolaryngoscopy — VLs are more expensive than direct laryngoscopes. However, it is not clear whether other costs of care may be reduced by using videolaryngoscopy. Relative costs were compared in a retrospective study of three years of data from the Premier Healthcare Database in the US, including approximately 28,000 patients (7000 intubated with VL, 21000 with DL) who had elective surgery lasting >one hour [67]. Patients who were intubated with VLs had lower average total hospital cost, lower length of hospital stay, and lower ICU admission rates, compared with those who were intubated with DL, though the differences varied with the type of surgery performed. Conclusions from the study are limited by its retrospective nature, lack of information on patient medical conditions, and lack of most details regarding the intubation (eg, difficulty, number of attempts, intubation time).

OPTICAL STYLETS — Optical stylets (OS) are rigid or semirigid tubular devices that fit inside the tracheal tube and convey an image using either fiberoptic bundles within the device, or a CMOS video chip at the distal end [9,10]. OS are not as commonly used as VLs. Whereas these devices require less mouth opening than VLs (theoretically only enough to accommodate an endotracheal tube [ETT]), they generally provide a more limited visual field than VLs.

Devices — The most commonly used OS are the Bonfils Retromolar Intubation Fiberscope (Storz), C-MAC Video Stylet (Storz), Levitan FPS (Clarus), and Clarus Video System (Clarus), which will be discussed here; other devices exist. The adult versions of these devices have a 5 mm outer diameter, which allows the use of ETTs ≥5.5 mm internal diameter. All of them are susceptible to fogging and should be prepared with an antifog solution or kept warm until used. The tip of the stylet must remain recessed within the ETT to avoid tissue injury.

●The Bonfils Fiberscope is a rigid scope, 40 cm in length, which contains fiberoptic and light bundles. The distal end is curved upward to 40 degrees. The image can be viewed via an adjustable eyepiece or with a video camera displayed on a monitor (picture 17) [68]. An uncut ETT can be used with this scope.

●The C-MAC Video Stylet is a recent addition to the C-MAC system. A proximal control lever can be activated to bend the distal tip of the stylet anteriorly by up to 60 degrees with a loaded ETT in place; releasing the lever returns the scope to a straight conformation. As its name suggests, this is a video-based device, compatible with C-MAC monitors. It accepts tube sizes 6.0 mm internal diameter and larger, with no need to cut the tube.

●The Levitan FPS consists of a 30 cm long semimalleable metal shaft containing fiberoptic and light bundles. Light source options include a battery powered light-emitting diode (LED), or a laryngoscope handle. The ETT must be cut to 28 cm to fit properly on this device (picture 18).

●The Clarus Video System (also marketed under the names Optiscope and Trachway) consists of a 31.7 cm long semimalleable stylet with a distally positioned CMOS video chip, a white LED light to illuminate the airway, and a red LED intended for transillumination of the neck. Size 7.0 and 7.5 mm ETTs can usually be used uncut; larger sizes or longer tubes should be cut, making sure that the stylet does not protrude from the tip of the tube (picture 19). The video image can be viewed on a 4-inch LCD screen attached to the handle, or on a larger monitor using a USB port. A longer version of the Clarus Video System is available for use with a double lumen ETT.

Optical stylet technique — OS can be used in two ways, either in conjunction with a laryngoscope, or as the sole device. Use of an OS without a laryngoscope requires discipline and experience to sequentially identify anatomical landmarks as reference points.

●Prepare the tip of the stylet by coating it with an antifogging solution. Alternatively, the ETT/stylet can be kept warm until it is ready for use.

●Lightly lubricate the stylet and insert it into the ETT, making sure that the tip of the stylet resides close to but within the distal tip of the ETT.

●Position the patient as for optimal mask ventilation and direct laryngoscopy.

●If applicable, shape the stylet (ie, if using a semimalleable scope). (See 'Devices' above.)

●Insert the OS into the mouth. The Bonfils stylet is designed primarily for retromolar insertion but can also be inserted in the midline. No comparisons of the two techniques have been published. The other OS were intended for midline insertion, but have also been used with a retromolar approach (movie 5).

●Using the free (usually nondominant) hand, perform a jaw thrust with the thumb and forefinger to help create a patent upper airway lumen through which to advance the scope. Alternatively, an assistant can perform an external jaw thrust, particularly if there are loose teeth.

●Advance the OS slowly, using reference structures, such as the uvula and epiglottis. This is particularly important to help maintain spatial awareness, because of the narrow field of vision of some of these devices.

●Once identified, continue to advance the OS with its loaded ETT beneath the epiglottis and through the vocal cords. Release jaw thrust to free up the nondominant hand and advance the ETT further into the trachea while withdrawing the OS by rotating the device towards the feet.

An OS can also be used to intubate while using direct or videolaryngoscopy to identify the epiglottis. For this technique, insert the OS beneath the epiglottis, using an external jaw thrust to lift the epiglottis if necessary. Then advance the OS and ETT through the vocal cords to complete intubation, as described above.

Intubation success with optical stylets — Limited studies have reported a range of success rates for intubation with OS, 86 to 100 percent [69-72], although it must be noted that many of these studies were conducted by early adopters and/or experienced users of OS devices; similar results may not occur in the hands of novice users. Case reports and series have reported successful use of various OS for awake intubation [73], nasal intubation [74], double lumen tube placement [75,76], and as a rescue device after failed direct laryngoscopy [77]. Examples of studies are as follows:

●Overall success – Reported success rates with OS are generally high in the hands of experienced users.

•In one prospective observational study, 390 out of 400 patients scheduled for elective surgery were intubated with the Bonfils Fiberscope on the first attempt by one of two experienced users [78]. Six patients required >1 attempt, and 4 patients could not be intubated with the Bonfils scope.

•In a retrospective review of 301 adults who underwent rapid sequence induction and intubation with the Levitan FPS, all but one patient were successfully intubated by an experienced user [70]. The mean time to intubation was 23 seconds.

●Success with difficult airway – Studies that have compared the use of OS for simulated difficult airway management have reported conflicting results.

•Compared with direct laryngoscopy (DL) – In a randomized trial of 76 elective surgical patients in whom a difficult airway was simulated with a rigid cervical collar to create limited mouth opening and restricted cervical spine movement, tracheal intubation was successful within two attempts in 82 percent of patients who were intubated with the Bonfils Fiberscope, compared with 40 percent of patients intubated using DL with a Macintosh blade [79].

•Compared with videolaryngoscopy (VL) – By contrast, in another randomized trial including 367 patients underwent elective spine surgery with manual inline cervical spine stabilization during intubation, first attempt intubation success was higher with the McGrath MAC VL, versus the Clarus Video System (Optiscope) device (92.3 versus 81 percent), and intubation time was shorter with the McGrath (35.7 ± 27.8 versus 49.2 ± 43.8 seconds) [80]. The devices were used by two experienced study investigators [80].

Predictors of difficult intubation with OS — The predictors of difficult intubation with OS are not well defined. In one study, predictors of longer intubation times with the Bonfils Fiberscope included limited mouth opening, increased body mass index, and high Cormack-Lehane intubation grade on DL [78].

COMPLICATIONS — Complications may occur whenever the airway is instrumented.

●Videolaryngoscopy – Injuries to teeth, soft tissues of the pharynx and hypopharynx, vocal cords, and trachea have been described with videolaryngoscopy [81-84]. In a large multicenter trial, pharyngeal injury occurred in 1 percent of 1100 patients with predictors of difficult laryngoscopy who were randomly assigned to intubation with the GlideScope or the C-MAC D-blade [83]. There was no difference in the rate of complications between the two devices.

These authors believe that most injuries are caused by inappropriate use of VLs, and that they can be avoided by directly watching the initial insertion and advancement of the laryngoscope and the endotracheal tube (ETT; rather than looking at the monitor) until the blade and ETT tips have been advanced beyond the soft palate or camera. (See 'Videolaryngoscopy technique' above.)

●Optical stylets – There have been fewer publications involving OS compared with VL, and therefore fewer reported complications. The few reported complications consist of airway trauma [71], and technical difficulties resulting from fogging and secretions.

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" and "Society guideline links: COVID-19 – Index of guideline topics".)

SUMMARY AND RECOMMENDATIONS

●Advantages of indirect laryngoscopy – Video laryngoscopes (VLs) and optical stylets (OS) allow visualization of the vocal cords and related airway structures without a direct line of sight. VLs improve the view of the glottis, and may increase intubation first attempt success rate, and may reduce the number of failed intubations, hypoxemic events, and esophageal intubations, particularly in patients with difficult DL. They have become part of various difficult airway algorithms. (See 'Advantages of video laryngoscopes and optical stylets' above and 'Intubation success and outcomes with video laryngoscopes' above.)

●VLs – The various available VLs are described above. (See 'Non-channeled VL' above and 'Channeled VL' above.)

•VLs can be categorized according to the shape of the blade (ie, Macintosh style or acute angle), and whether or not they have a channel that guides endotracheal tube (ETT) advancement. (See 'Classification of video laryngoscopes' above.)

•Macintosh style VLs can be used for direct or indirect laryngoscopy. (See 'Macintosh-style VL' above.)

•Acute angle blade VLs allow indirect visualization of more anterior laryngeal structures. A stylet is used to guide the tip of the ETT into the glottis with these devices. (See 'Acute-angle blade VLs' above.)

•Channeled VLs are bulkier than most non-channeled VLs. (See 'Channeled VL' above.)

●VL technique – Important technical points for indirect laryngoscopy include the following, with details provided above (see 'Videolaryngoscopy technique' above):

•When using all types of VLs, look in the patient's mouth, not at the video screen, when inserting the laryngoscope and the ETT into the oropharynx, to avoid injury of the teeth and soft tissue. Advance the ETT under direct vision until the tip is beyond the soft palate.

•For laryngoscopy with a Macintosh style VL, position the patient as for optimal direct laryngoscopy. For laryngoscopy with an acute-angle blade, the patient's head and neck can be positioned in a "sniffing," or neutral position.

•Turn on the device at least one minute prior to laryngoscopy, to warm the camera and minimize condensation on the lens.

•Place the VL blade in the midline and advance only as deeply as necessary to visualize the glottis, to avoid downfolding of the epiglottis.

•When using a channeled VL, direct the ETT by manipulating the VL to aim the ETT in the desired direction. (See 'Channeled VL' above.)

●VL versus DL

•In clinicians experienced with VL, intubation success with VL is similar to or greater than with direct laryngoscopy, and may reduce the incidence of failed intubation, peri-intubation hypoxia, and esophageal intubation. (See 'Intubation success and outcomes with video laryngoscopes' above.)

•We and some other UpToDate contributors use VL rather than DL for first attempt at intubation for all patients when possible. Other UpToDate contributors use VL selectively, depending on patient factors and the clinical situation. (See "Airway management for induction of general anesthesia", section on 'Choice of intubation technique'.)

●Optical stylets – OS are rigid or semirigid tubular video devices that fit inside the tracheal tube and are used to guide the ETT through the vocal cords. OS require less mouth opening, but many provide a more limited visual field than VLs. Examples of devices are described above. (See 'Devices' above.)

●OS technique – An OS can be used alone, or a laryngoscope can be used to visualize the epiglottis before inserting the OS. Especially with stand-alone use, a jaw thrust should be used to help elevate the epiglottis before advancing the OS. Details of the OS technique are described above. (See 'Optical stylet technique' above.)

●Complications – Reported complications with the use of VLs include injuries of teeth, soft tissues of the pharynx and hypopharynx, vocal cords, and trachea. Many injuries may be avoided by directly watching the insertion and advancement of the laryngoscope and ETT (rather than watching the monitor) until the tip is beyond the soft palate. There is little data on complications with OS. (See 'Complications' above.)