Chapter 25 Video Laryngoscopes
Although the use of video laryngoscopy for teaching the routine laryngoscopic technique of endotracheal intubation and for managing a difficult airway have been known for some years, anesthesiologists have been slow to recognize these advantages. Video-assisted techniques have been successfully used for decades in many surgical disciplines and have largely replaced open approaches in areas such as arthroscopy and laparoscopy (Box 25-1).The magnified and detailed view of the surgical site on a monitor makes it easier to coordinate the work of the surgical team and provides an effective teaching tool for novices. Anesthesiologists have observed this development with interest but without realizing its potential for their own specialty. For years, anesthesiologists have applied video technology almost exclusively for imaging in bronchoscopy and fiberoptic intubation, but the past decade has witnessed some important innovations in the field of video-assisted airway management.
Box 25-1 Important Indications for Video Laryngoscopy
In 1996, Levitan introduced a video camera attached to a head ring (Airway Cam). With this technique, intubation performed with a standard laryngoscope is displayed on a video monitor so that it can be observed by other personnel in the room. The view of the glottis matches the visual field of the intubating physician and does not improve visualization of the glottic plane.
Another principle forms the basis for development of modern video laryngoscopes (VLs). By integrating optical image guides and video cameras into standard laryngoscopes, a magnified and detailed view can be displayed on an external monitor while conventional direct laryngoscopy is performed. Various investigators made an effort to advance this principle and integrated rigid or flexible fiberoptics into laryngoscopes with different shapes, such as the WuScope,1 Bullard,2 and UpsherScope.3 Henthorn and coworkers reported the combination of a flexible fiberoptic cable with a conventional Miller laryngoscope blade,4 which they used for student education. Instructors and trainees found this forerunner of modern VLs to be helpful in identifying the anatomy of the upper airways and successfully performing the intubation.
In 2001, Weiss and associates described a Macintosh laryngoscope, the angulated video-intubation laryngoscope (AVIL), in which a thin fiberoptic cable can be advanced through a guide channel in the laryngoscope handle and blade to a point very close to the blade tip.5 Adapters can be used to connect the fiberoptic cable to an external video unit, enabling a close-up view of the larynx to be displayed on an external monitor. Another option is to introduce the video scope into the endotracheal tube (ETT). However, there have been no other publications on this device from other users, and it apparently has not found wide application.
The X-Lite (Rüsch, Duluth, GA) was introduced in 2001 in Vienna. This commercially available VL has an image guide built into the blade and a video camera installed in the handle. It was the first design to offer interchangeable blade shapes and sizes that could be connected to the camera handle. Two fairly bulky and heavy cables (i.e., light and image guides) emerge from the end of the handle. These characteristics made the device more cumbersome than a conventional laryngoscope, made the device less rugged and more susceptible to technical flaws, and hampered cleaning and disinfection.
In 2004, Kaplan and Berci introduced a further improvement of a Macintosh VL, a direct coupled interface VL (DCI, Karl Storz, Tuttlingen, Germany), also known as the VMS or V-MAC.6 The DCI has an integrated camera and connectable blades equipped with a fiberoptic light and image guide, and the handle and blade are combined in a fixed unit.
Miniaturization of camera chip technology; improved, rechargeable battery power and light output; and affordable, small liquid crystal display (LCD) monitors made video laryngoscopy a booming technology, which led to the introduction of different types of VLs. Because VLs have different shapes, technical equipment, and applications, further classification of these devices is justified.7 The main difference in VLs arises from the type of blade that is incorporated into the system. VLs that are based on a conventional, established blade shape, such as the Macintosh blade, have the option of visualizing the glottic entrance by direct laryngoscopy. Users are familiar with the handling of this blade type. Other VLs are designed with highly curved or angled blades that pass around the tongue and allow a “look around the corner” to the glottic opening. These VLs allow the best visualization of the glottis, although a direct view of the glottic entrance usually is impossible (i.e., obligatory indirect visualization). Because of the high degree of blade angulation, they must be used with a malleable or rigid styletted tube in most cases.
A subcategory of obligatory indirect laryngoscopes has a tube-guiding channel incorporated in the curved blade. This design obviates the use of a tube stylet to guide the tube to the glottic entrance, but it also does not allow correction of the direction of the tube.
For hygienic purposes, all VL systems are available in disposable forms. Compared with the reusable, stainless steel designs that allow lower blade profiles, the disposable versions mainly use a plastic blade sheath, which causes slightly larger blade profiles.
VL systems are available with an external or internal monitor. The larger external monitor allows better orientation for the laryngoscopist and operating staff, who may actively help with the intubation process (e.g., extralaryngeal maneuvers, suction). In systems with integrated monitors, visual orientation is more difficult on the smaller monitors. Others cannot easily follow the intubation process on the small monitor; this limitation may be aggravated by adverse space or light conditions. Picture or video documentation that can be obtained with external monitors usually is not available with the compact design of the smaller monitor. The greatest advantages of the systems with integrated monitors are their unrestricted mobility and minimal light and space requirements, which make them valuable for use in the prehospital setting. Because all these devices are battery operated, attention should be paid to the battery capacity to prevent a system blackout during intubation.
The A.P. Advance (Venner Medical, Kiel, Germany) is a mobile VL that consists of a battery-containing handle, a blade core, and a 3.5-inch LCD monitor that connects to the handle magnetically. The size of the integrated monitor is bigger than in competitive VLs; using National Television System Committee (NTSC) video output, the monitor signal can be exported to an external screen. The monitor has an integrated, rechargeable battery, which provides the monitor screen and handle with power. The light source of the blade receives power from a battery integrated in the handle, and the handle and blade may be used without a monitor attached (i.e., conventional direct laryngoscopy).
The blade core can be used with three types of disposable blade sheaths. Two blades are adapted to the classic Macintosh shape (sizes 3 and 4), and one, the difficult airway blade (DAB), has been developed for use in the difficult airway. The DAB has a specific distal angulation and houses a tube-guiding channel in the distal one third of the blade, providing an obligatory indirect glottic view. For blade types with a guiding channel, the epiglottis should be lifted directly by the blade tip of the DAB, similar to the straight blade technique employed with a Miller blade.
No clinical experience has been published for the A.P. Advance, but in two mannequin studies, medical professionals used it in normal and difficult airway scenarios and reported good visualization and intubation success.8,9 In another mannequin study, paramedics who had not previously used video laryngoscopy achieved earlier intubation and fewer unplanned advances of the tube compared with use of the GlideScope Ranger.10
The DCI video laryngoscope was designed using a modified Macintosh blade with the same curvature as the original 1943 version and a laryngoscope handle. The batteries in the handle are replaced with a small video camera (i.e., DCI camera) and a combined image-light bundle that inserts into the Macintosh blade.6 The DCI video laryngoscope system allows interchange of different devices, such as laryngoscopes (e.g., Macintosh, Dörges, Miller, D-Blade) and rigid (e.g., Bonfils intubation endoscope) and flexible fiberscopes (Fig. 25-1); however, mobility of the fiberoptic-based system is limited. The DCI system has been displaced by the mobile C-MAC video intubation system.
Component of the DCI video laryngoscope system are assembled, and an antifog solution is applied to the tip of the image-light bundle. If a regular Macintosh blade is used, conventional direct laryngoscopy may be performed. On insertion of the scope into the patient’s mouth, the image can be viewed on the video monitor. Even if the familiar Macintosh blade technique is used with this device, the distal viewing bundle may necessitate less anterior lift on the blade and may permit a view of part or all of the glottic opening in otherwise difficult laryngoscopies.
Kaplan and associates reported a series of 235 patients in whom they used the DCI video laryngoscope system.6 Of these cases, 217 were predicted to be straightforward, and in all but one, the DCI video laryngoscope system was successfully used, with 10% requiring external laryngeal manipulation. A second group of 18 patients had anatomic predictors of difficult laryngoscopy; all in this group required external laryngeal manipulation but were successfully intubated with the DCI video laryngoscope system. In another study, Kaplan and colleagues compared the view obtained using DCI by direct vision with that obtained on the monitor and found that the image on the monitor was the same as or better than the direct line-of-sight view in most patients undergoing routine anesthesia.11 Hagberg and colleagues describe the successful use in a patient who previously had an unexpected difficult laryngoscopy and impossible intubation and who was subsequently intubated with the DCI system after the first attempt.12
The C-MAC (Karl Storz, Tuttlingen, Germany) video laryngoscope system is a modification of the Storz DCI system. The C-MAC VL can provide a useful alternative during routine induction of general anesthesia and in securing a difficult airway. The C-MAC is based on a modified Macintosh blade that has the same curvature as the original 1943 version,13 but it is different from the original Macintosh blade in its thinner profile (maximum of 14 mm) and its beveled shoulder, which reduces the risk of oral and dental injury and facilitates insertion in patients with limited mouth opening. Optionally, the blade may be equipped with a guide channel for introducing a suction catheter to help maintain a clear visual field during laryngoscopy. The C-MAC system is compatible with various blades. The electronic module (E-module) fits into the blade handle and allows a rapid exchange of Macintosh stainless steel blade sizes 2, 3, and 4, Miller sizes 0 and 1, and the D-Blade. A clip-on camera (C-CAM) can link the C-MAC system with rigid or flexible fiberoptics. The combined optical system of the C-MAC consists of a complementary metal-oxide semiconductor (CMOS) chip set (320 × 240 pixels), an optical lens with an aperture angle of 80 degrees, and a high-power, light-emitting diode (LED) at the distal third of the blade with effective antifogging properties. The blade handle with the E-module and the external, 7-inch LCD color monitor have push buttons that allow the operator to capture images from the screen and record video sequences, which are storable on standard SD memory cards, which have a 2-GB capacity. In the rare case that visualization of the glottic opening is still difficult, the D-Blade may be attached to the system within seconds. The higher curvature of the D-Blade allows a better look around the corner, and the low blade profile may permit use even in patients with limited mouth opening (e.g., 15 mm); however, direct laryngoscopy is not possible in most cases.
Other parts of the C-MAC system include the C-MAC pocket monitor (PM), which is a 2.4-inch LCD monitor combined with a lithium-ion battery–equipped E-module that fits in all available blades of the C-MAC system (e.g., Miller 0 and 1, Macintosh 2-4, D-Blade). The rechargeable battery supplies the monitor and the LED light source of the blades with 1 hour of energy without recharging, so that the VL is fully portable and can be used wireless. Power is turned on by a magnetic switch when lifting the monitor. Because this system is designed for mobile use, there are no other switches or connections for picture or video recording and exportation. To save battery capacity, the monitor turns off after 10 minutes automatically.
For portable use, the monitor and blade handles can be packed separately in a rugged carrying bag, which permits use of all monitor buttons through the bag, even under difficult ambient conditions (e.g., prehospital settings). The C-MAC PM uses the identical blades, and the laryngoscopic technique is the same as with the conventional C-MAC system. However, successful handling of the device with the small monitor needs to be tested in clinical trials.
Several investigators showed superior visualization of the glottis with the C-MAC compared with conventional direct laryngoscopy.14–17 Even if the application of a stylet cannot be eliminated completely, most intubations using a C-MAC VL can be performed without stylet use.18,19 In a preliminary study by Cavus and associates of patients in whom conventional Macintosh laryngoscopy failed, use of the C-MAC D-Blade provided better glottic visualization and intubation success in all patients.20 An observational study of 80 patients with the need for out-of-hospital emergency intubation (e.g. trauma, cardiopulmonary resuscitation) performed by physicians showed good handling and intubation success with the C-MAC VL. In a few cases, video laryngoscopic intubation was impossible due to VL problems such as bright surrounding light, and only direct laryngoscopy with the same device resulted in fast, successful intubation.17
The McGrath MAC (Aircraft Medical, Edinburgh, United Kingdom) is a slim-profile, mobile VL that consists of a battery-containing handle, a steel blade core (CameraStick), and a 2.5-inch LCD monitor fixed to the handle. The proprietary lithium-ion battery pack provides approximately 250 minutes of power. The McGrath MAC is fully immersible for high-level disinfection. As in the McGrath Series 5 VL, there is no connection port to transfer the image to an external monitor.
The McGrath MAC may be used with disposable Macintosh blades (sizes 3 and 4); there are no blades with higher angulation (as in the McGrath Series 5 VL) available for this VL. Because of the Macintosh blade shape, direct and indirect laryngoscopy can be performed.
The GlideScope Direct (Verathon Medical, Bothell, WA) is a stainless steel Macintosh blade that adds to the existing GlideScope system (see “Video Laryngoscopes Using Highly Curved Blades”). The purpose of this blade is to expand the system with the option to teach conventional laryngoscopy because the GlideScope Direct allows direct and indirect (video laryngoscopic) glottic visualization.
The GlideScope Direct is primarily designed as an intubation trainer, but may also be used for clinical use. Due to the Macintosh shape, the GlideScope Direct provides both direct and indirect laryngoscopic view. It is available as a reusable and single-use device. In cases that need a more highly curved blade (e.g., GlideScope AVL, GVL), the whole blade including the cable has to be changed.
The Truview picture capture device (PCD) VL (Truphatek International Limited, Netanya, Israel) has an integrated optical lens (optical view tube), a unique 42-degree blade tip angulation, and a view through a 15-mm eyepiece. The LED light source is stored in the handle, and the light is transmitted to the blade tip by fiberoptic strands. It is available in five blades sizes, and all of them allow direct laryngoscopy.
The blades are equipped with an integrated oxygen jet cleaning and insufflation system, which can connect to an external oxygen flow meter and provide oxygen at a rate of 4 to 6 L/min. The video properties of the optical Truview blade can be achieved by magnetic connection of the eyepiece to the camera of the Truview PCD screen.
The Truview may be used like a conventional laryngoscope. Additional defogging maneuvers should be performed. The blade has an integrated channel that may allow apneic oxygenation of the patient during laryngoscopy.
The glottic view may be improved by use of the Truview compared with conventional laryngoscopy with a Macintosh blade, and this may result in a higher intubation success rate in difficult-to-manage airways.22–25 Compared with conventional laryngoscopy with a Macintosh laryngoscope, intubation with the Truview may take more time, but intubation success rates may be comparable; however, rates of airway morbidity related to laryngoscopy may be lower.23 In a study by Carlino and colleagues using the Truview as a teaching tool for anesthesiology residents, intubation success after the first attempt was almost doubled compared with that for conventional Macintosh laryngoscopy.26 In patients with cervical spine immobilization, Malik and colleagues experienced inferior visualization and intubation compared with other VLs. The handling may be cumbersome, and fogging may impair visualization process.22