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INTRODUCTION — Video laryngoscopes (VLs) and optical stylets (OSs) 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. In contrast, OSs 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 OSs, 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 "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 rural hospitals and during prehospital emergency airway management .
Video laryngoscopy 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 a video laryngoscope (VL) 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 video laryngoscopes [4-8].
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]. Some VLs (eg, the C-MAC) are available with a Miller style blade, only in pediatric sizes. (See "Devices for difficult endotracheal intubation in children", section on 'Video laryngoscope'.)
Non-channelled 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 is passed through the vocal cords independent of the device. Non-channelled 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 channelled version, both of which have a blade shaped to match the anatomic curve of the upper airway and more like an acute-angle blade than a conventional Macintosh-style blade.
Macintosh-style VL — The technique for use of a Macintosh-style VL is similar to the use of the Macintosh blade for DL, and these devices can be used for both indirect and direct laryngoscopy. Therefore, they are useful for teaching and supervising DL, since the instructor can see on the monitor the same view the trainee sees while performing DL. Examples of VLs with Macintosh-style blades include the C-MAC (picture 3 and picture 2A), the Glidescope Mac-T, and the McGrath MAC (picture 4).
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 several of the Glidescope products (LoPro Titanium, AVL, and Ranger), C-MAC D-blade, and the McGrath EDL-X blade (picture 5 and 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 a 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 endotracheal tube 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 . A specialized rigid stylet is available for the Glidescope, with a 70 degree bend angle (picture 10).
Channelled VL — Channelled 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. Channelled VLs are bulkier than those without channels since they must accommodate an endotracheal tube adjacent to the optical and light-emitting diode (LED) elements. Therefore, these devices may not be appropriate for patients with severely limited mouth opening.
The most widely used channelled VLs are the Airtraq Avant (picture 11 and picture 12 and picture 13), Airway Scope (Pentax) (picture 14), and King Vision (Ambu) (picture 15). All of these laryngoscopes are entirely disposable or have single-use components. The channelled 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 can be used with channelled or non-channelled blades.
Other distinguishing features of VLs — A number of features differ among the many available video laryngoscopes, and these features change with advances in technology [14-16]:
●Sizes available (eg, pediatric and adult) (see "Devices for difficult endotracheal intubation in children", section on 'Video laryngoscope')
●Blade thickness, which is particularly important in patients with small mouth opening
●Availability of reusable and single use versions
●Resolution of the video camera or display
●Monitor size, lighting, resolution, portability, input and output options
●Ability to save images and videos (eg, with SD card or USB drive)
●Cost per use
Video laryngoscopy technique — When using all types of VLs, the operator should be looking in the patient’s mouth, not at the video screen, when inserting the laryngoscope and the endotracheal tube into the oropharynx, to avoid injury of the teeth and soft tissue. The laryngoscope should be inserted under direct vision as far as possible, and the endotracheal tube should be advanced under direct vision until the tip is beyond the VL camera, or beyond the soft palate. An example of a soft tissue injury as a result of watching the monitor rather than the endotracheal tube is shown in a video (movie 1).
Proficiency with the use of video laryngoscopes 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 the C-MAC 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.
●Insert a stylet in the endotracheal tube ensuring that the tip does not protrude beyond the endotracheal tube (ETT). A stylet will increase the likelihood of success on the first attempt, though it may prove to have been unnecessary .
●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, advancing the laryngoscope only as deeply as necessary to place the tip in the vallecula, to avoid downfolding of the epiglottis .
●If the direct view is suboptimal, check the indirect view on the monitor as this may offer 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 .
●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 advancing the ETT.
Acute-angle blade VL technique — The technique for laryngoscopy using the Glidescope 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 or tracheal introducer into the ETT, making sure that the tip of the stylet does not protrude beyond the end of the ETT.
●Position the head and neck in a neutral position, avoiding neck flexion. Obese patients should be placed in the ramped position, because it offers a physiologic and mechanical advantage for ventilation. It is unknown whether the ramped position assists with laryngeal visualization when video laryngoscopy is used (figure 1). (See "Anesthesia for the obese patient", section on 'Patient positioning'.)
When the tragus of the ear is levelled with the sternal angle, as it is in the ramped position, insertion of the laryngoscope blade into the patient’s mouth may be difficult. This may also happen when cricoid pressure is applied, as the assistant’s hand may interfere with the laryngoscope handle. In such circumstances, removal of the pillow immediately prior to laryngoscopy may facilitate blade insertion. (See "Rapid sequence induction and intubation (RSII) for anesthesia", section on 'Cricoid pressure'.)
●Lubricate the VL blade lightly to facilitate passage around the tongue (ensuring that lubricant is not applied near the camera).
●Open the patient’s mouth, and insert the blade in the midline, under direct vision. Rotate the blade in the sagittal plane around the base of the tongue, watching the monitor, and avoid excessively deep 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 two additional benefits:
-A wider visual field
-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
●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. Advance the ETT until the tip passes the palate; then attention should be redirected 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, partially withdrawing the stylet as the tube is gently advanced into the trachea.
Troubleshooting non-channelled video laryngoscopy — Although video laryngoscopy is usually straightforward, problems with insertion of the laryngoscope or the endotracheal tube 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 into the mouth and slide it to the right before introducing the VL blade.
●Difficulty directing the ETT to the larynx — A flexible scope along with the VL can be used to direct the tip of the ETT between the vocal cords. Alternatively, a dynamic or articulating stylet can be used (eg, Parker Flex-It Stylet, or Truflex articulating stylet) (picture 16 and picture 17).
●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, gently rotate the ETT to disengage the tip from the anterior tracheal rings. If this maneuver is unsuccessful, insert a coude shaped bougie or flexible scope though the ETT into the trachea, and advance the ETT over it.
Channelled 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 before a stable image appears.
●Apply a film of 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. Rotate the blade in the sagittal plane around the base of the tongue, watching the monitor, until the arytenoids are seen.
•Airtraq/Channelled 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. Rotation, elevation, depression, or external laryngeal pressure may help align the 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 difficult to insert in a patient with a small mouth. Insert the blade into the mouth and then beneath the epiglottis, similar to placement of a straight DL blade. This is not always possible, and an alternative airway device may be required. Elevate the laryngoscope gently to reveal the larynx, and manipulate the laryngoscope and ETT as for the Airtraq to advance the ETT through the vocal cords and into the trachea.
●Remove the channelled VL carefully, making sure the ETT remains in place. For the Airtraq, deflect the proximal ETT anteriorly to disengage the ETT from the retaining tab in the channel (picture 13). The VL can be rotated slightly anticlockwise while the ETT is rotated in the opposite direction. The ETT should be stabilized by an assistant while the Airtraq is rotated out of the mouth. The King Vision Scope and AWS can be simply withdrawn by reversing the direction used during its insertion, carefully ensuring that the ETT remains in place.
Intubation success with video laryngoscopes — In general, high rates of success are reported for intubation with VLs. Successful intubation is achieved in >95 percent of patients with normal airways with the use of VLs [19,20].
●VLs versus DL with Macintosh blade — Many studies have reported improved laryngeal view with the use of VLs in patients without predictors of difficult laryngoscopy [21-24]. Intubation success rates with VLs in such patients are high, and similar to success rates for DL by experienced clinicians [19,25].
Importantly, VLs may improve intubation success in patients with difficult or failed DL, and these devices have become part of various difficult airway algorithms [26-29]. Benefits of VLs have been reported in patients with predicted [23,30,31], encountered , or simulated  difficult intubation, rapid sequence intubation , obese patients [34,35], and patients with immobilized cervical spines .
A metaanalysis of 64 randomized trials with over 7000 patients that compared the use of various VLs with DL with a Macintosh blade concluded that VLs improve the glottic view, and may reduce the number of failed intubations, particularly in patients with a difficult airway . There were no differences in the number of intubation attempts or time required for intubation.
Another metaanalysis of 17 randomized trials that compared Glidescope intubation with DL reported that the Glidescope was associated with improved glottic visualization, particularly in patients with predicted or simulated difficult intubation . VL increased first attempt success among non-experts, and, when results were pooled, there was no difference in intubation time. There was marked heterogeneity among studies for all of these outcomes.
A number of studies have reported that Glidescope intubation may fail despite an excellent view of the larynx [20,38]. The authors of this topic are of the opinion that this reflects limited appreciation of the differences between DL and VL , and that a good laryngeal view should almost always be followed by intubation success.
Intubation times reported in studies comparing DL and VL vary widely, and are difficult to interpret because of heterogeneity among patient populations 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 [40-43].
Much of the literature on VL has emphasized its value for the less experienced laryngoscopist . 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 . Consistent with this result, two studies have reported increased success rates with Glidescope intubation at institutions where it was used more frequently [45,46].
●Comparison among VLs — High rates of successful intubation are reported in normal airways for all the VLs discussed here, with clinically marginal or no differences among them. A number of studies have compared the performance of various VLs in patients with predictors for difficult laryngoscopy and intubation. The optimal VL for a specific clinical scenario probably varies, depending on patient characteristics and the laryngoscopist’s familiarity with the device. As an example, bulkier devices may be less useful in patients with restricted or small mouth opening. Devices with long handles and increased blade angulation (eg, King Vision Scope) may be difficult to insert in the mouths of patients with limited cervical extension, short necks, or large chests.
•A metaanalysis of 24 randomized trials that compared various VLs (ie, Airtraq, Airwayscope, C-MAC, Glidescope, and McGrath) with Macintosh blade DL in patients with cervical spine immobilization reported that only the Airtraq device reduced the risk of intubation failure .
•In one study, over 700 elective surgical patients were randomly assigned to intubation with one of six video laryngoscopes, while mouth opening and neck mobility were restricted by a rigid cervical collar . First attempt intubation success rates were highest with the McGrath (98 percent) and C-MAC D blade (95 percent), followed by the King Vision (87 percent), Glidescope (85 percent), Airtraq (85 percent), and A.P. Advance (37 percent).
●Predictors of difficult intubation with VL — Difficult and failed video laryngoscopy do 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 video laryngoscopy as difficult have not been 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 .
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 . 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 . (See "Airway management for induction of general anesthesia", section on 'Airway examination'.)
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]. Optical stylets (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), they provide a more limited visual field than VLs.
Devices — The most commonly used OSs are the Bonfils Retromolar Intubation Fiberscope (Storz), Levitan FPS (Clarus), and Clarus Video System (Clarus), which will be discussed here. The adult versions of these devices have a 5 mm outer diameter, which allows the use of endotracheal tubes ≥5.5 mm internal diameter. All of them are susceptible to fogging and should be prepared with an anti-fog solution or kept warm until used. The tip of the stylet must remain inside the endotracheal tube 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 18) . An uncut endotracheal tube can be used with this scope.
●The Levitan FPS consists of a 30 cm long semi-malleable metal shaft containing fiberoptic and light bundles. Light source options include a battery powered light-emitting diode (LED), or a laryngoscope handle. The endotracheal tube must be cut to 28 cm to fit properly on this device (picture 19).
●The Clarus Video System consists of a 31.7 cm long semi-malleable 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 endotracheal tubes (ETTs) can usually be used uncut; larger sizes or longer tubes should be cut so that the stylet does not protrude from the tip of the tube (picture 20). 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 — Optical stylets 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 anti-fogging 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 semi-malleable scope). (See 'Devices' above.)
●The OS may be used alone, or a laryngoscope can be used to identify the epiglottis before insertion of the OS.
•Use of the OS as the sole device — With this method, the OS is used to identify all airway structures, as follows:
-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 OSs were intended for midline insertion, but have also been used with a retromolar approach (movie 5).
-Advance slowly, using reference structures such as the uvula and epiglottis. This is particularly important because of the narrow field of vision with these devices.
-Identify the epiglottis, and using the free hand, perform a jaw thrust with the thumb and forefinger, to reveal the vocal cords. Alternatively, an assistant can perform an external jaw thrust, particularly if there are loose teeth.
-Advance the OS and the ETT through the vocal cords, and advance the ETT into the trachea while withdrawing the OS, rotating the device towards the feet.
•Use of the OS with a DL/VL — Laryngoscopy may be performed to identify the epiglottis prior to insertion of the OS, as follows:
-Perform laryngoscopy with a conventional or video laryngoscope held in the left hand.
-Position the OS, held in the right hand, beneath the epiglottis.
-If available, have an assistant perform a jaw thrust to elevate the epiglottis. If unassisted, set the laryngoscope aside, and perform a jaw thrust with the thumb and forefinger of the left hand, to reveal the vocal cords.
-Advance the ETT and remove the OS as above.
Intubation success with optical stylets — Limited studies have reported a wide range of success rates for intubation with optical stylets. In one prospective observational study, 396 out of 400 patients scheduled for elective surgery were intubated with the Bonfils Fiberscope on the first attempt by one of two experienced users . In this study, predictors of longer intubation times included small mouth opening, high body mass index, and high Cormack Lehane intubation grade on direct laryngoscopy. Reported success rates range from 86 to 100 percent depending on patient selection, prior experience, and the definitions of success (eg, first attempt, time-limited, limited number of permitted attempts) . Results with this device in experienced hands do not appear to be appreciably different from other VL or OS devices.
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 . The mean time to intubation was 23 seconds.
Optical stylets may be beneficial in patients with difficult laryngoscopy and intubation. In one study including 76 elective surgical patients, a difficult airway was simulated with the use of a rigid cervical collar to create limited mouth opening and restricted cervical spine movement. Intubation was successful in 82 percent of patients randomly assigned to intubation with the Bonfils Fiberscope, compared with 40 percent of patients assigned to direct laryngoscopy with a Macintosh blade .
To date, publications regarding the Clarus Video System are limited to case reports.
COMPLICATIONS OF VL — Complications may occur whenever the airway is instrumented. Injuries of teeth, soft tissues of the pharynx and hypopharynx, vocal cords, and trachea have been described with video laryngoscopy [54-57]. 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 . There was no difference in the rate of complications between the two devices.
This author believes that most injuries are caused by inappropriate use of VLs, and that they can be avoided by directly watching the insertion and advancement of the laryngoscope and the endotracheal tube (rather than looking at the monitor) until the tip passes beyond the soft palate or camera. (See 'Video laryngoscopy technique' above.)
COMPLICATIONS OF OS – Compared with VL, there have been fewer publications involving OS devices. Most of the reported complications relate to intubation failure though trauma , and technical difficulties resulting from fogging and secretions have also been described.
SUMMARY AND RECOMMENDATIONS
●Video laryngoscopes (VLs) and optical stylets (OSs) are rigid devices that allow indirect laryngoscopy, ie, visualization of the vocal cords and related airway structures without a direct line of sight. (See 'Introduction' above and 'Advantages of video laryngoscopes and optical stylets' above.)
●VLs can be categorized according to the shape of the blade (ie, Macintosh style or acute-angle), and whether or not they have channels that accommodate and guide endotracheal tube advancement. (See 'Classification of video laryngoscopes' above.)
•Examples of Macintosh style VLs include the C-MAC, the Glidescope Mac-T, and the McGrath MAC. These devices can be used for direct or indirect laryngoscopy. (See 'Macintosh-style VL' above.)
•Examples of acute-angle blade VLs include several of the Glidescope products, the C-MAC D-blade, and the McGrath EDL-X blade. These devices allow visualization of anterior laryngeal structures. A stylet is used to guide the tip of the endotracheal tube into the glottis with these devices. (See 'Acute-angle blade VLs' above.)
•Examples of channelled VLs include the Airtraq, the Airway Scope, and the King Vision. These devices are bulkier than most non-channelled VLs. (See 'Channelled VL' above.)
●Important technical points for indirect laryngoscopy include the following (see 'Video laryngoscopy technique' above):
•When using all types of VLs, the operator should be looking in the patient’s mouth, not at the video screen, when inserting the laryngoscope and the endotracheal tube into the oropharynx, to avoid injury of the teeth and soft tissue. The endotracheal tube should be advanced under direct vision until the tip is beyond the VL camera, or beyond the soft palate.
•For laryngoscopy with a Macintosh style VL, the patient should be positioned as for optimal direct laryngoscopy. For laryngoscopy with an acute-angle blade, the patient’s head and neck should be placed in a neutral position.
•The device should be turned on at least one minute prior to laryngoscopy, to warm the camera and minimize condensation on the lens.
•Airway structures should be visualized under direct or indirect vision, advancing the laryngoscope blade only as deeply as necessary, to avoid downfolding of the epiglottis.
•When using a channelled VL, the endotracheal tube is directed by manipulating the VL. (See 'Channelled VL' above.)
●VLs improve the view of the glottis, and may increase intubation success and reduce the number of failed intubations, particularly in patients with difficult DL. They have become part of various difficult airway algorithms. (See 'Intubation success with video laryngoscopes' above.)
●Predictors of difficult VL intubation are not well defined, but may include abnormal neck anatomy, thyromental distance <6 cm, limited cervical spine motion, small mouth opening, decreased jaw mobility, and the supine/sniffing position (table 1). (See 'Intubation success with video laryngoscopes' above.)
●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. OSs require less mouth opening, but provide a more limited visual field than VLs. Examples of commonly used OSs include the Bonfils Fiberscope, the Levitan FPS, and the Clarus Video System. (See 'Devices' above.)
●An OS can be used alone, or a laryngoscope can be used to visualize the epiglottis before inserting the OS. With either technique, a jaw thrust should be used to elevate the epiglottis, reveal the vocal cords, and facilitate advancement of the OS and endotracheal tube (ETT) between the vocal cords. (See 'Optical stylet technique' above.)
●Limited studies have reported a wide range of intubation success rates with the use of OSs. Success rates appear to be high with experienced users, including in patients with predictors of difficult laryngoscopy. (See 'Intubation success with optical stylets' above.)
●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 endotracheal tube (rather than watching the monitor) until the tip is beyond the soft palate or camera. (See 'Complications of VL' above.)
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- Russell T, Khan S, Elman J, et al. Measurement of forces applied during Macintosh direct laryngoscopy compared with GlideScope® videolaryngoscopy. Anaesthesia 2012; 67:626.
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