Chapter 25 Video Laryngoscopes
I Introduction
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.
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.
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.
II Video Laryngoscopes Using Macintosh-Based Blades
A A.P. Advance
3 Clinical Experience
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
B Direct Coupled Interface (DCI) Video Laryngoscope System
1 Description
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.
3 Clinical Experience
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
C C-MAC Video Laryngoscope System
1 Description
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.
3 Clinical Experience
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
F Truview Picture Capture Device
3 Clinical Experience
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
III Video Laryngoscopes Using Highly Curved Blades
High curvature of the blade typically makes it impossible to perform direct laryngoscopy; tracheal intubation requires indirect visualization. To follow the high curvature of the blade with an ETT, a tube guide or malleable stylet is necessary.18,19 Although there is a tendency to focus on the video monitor, it is important to directly visualize the tube going into the mouth and advancing beyond the tongue before it becomes visible on the monitor. Perforations of the pharynx and hypopharynx have occurred with the GlideScope and the McGrath when operators have blindly inserted styletted tubes while focusing only on the video monitor.27,28 Highly curved, indirect VLs can be used with almost no forces applied to tongue and pharyngeal structures, and these devices can be used in awake video laryngoscopic intubation as an alternative to awake fiberoptic intubation, assuming that attention is paid to possible contraindications for video laryngoscopy (e.g., mouth opening <15 mm, subglottic stenosis, tumor masses). Several case reports describe safe application of this technique.29–35
A GlideScope
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