Optimizing GlideScope® Laryngoscopy: An In Vitro  Study on an Airway Model

The GlideScope® Videolaryngoscope1*(GVL; Diagnostic Ultrasound Corporation, Bothell, WA, and Saturn Biomedical Systems Inc., Burnaby, British Columbia, Canada) has a video camera incorporated in the undersurface of its curved plastic blade, providing a detailed airway image on an integrated monitor. The shape of the GVL partially resembles the shape of the standard Macintosh laryngoscope (fig. 1A). However, a 60° upward angulation of the distal half of the blade allows for an easy visualization of the larynx, which is often better than that of a rigid laryngoscopy.2Despite better laryngoscopic view with the GVL, intubation using a Macintosh laryngoscope was significantly faster.2In addition, in one series of 728 patients, the intubation failure rate of the GVL was 3.7% despite the ability to obtain grade 1 or 2 views most of the time.3–5The paradox that the GVL provided better glottic visualization but not easy intubation may have been caused by patient-related factors, insufficient skills of intubators, and/or limitations of the device. Intubation with the GVL is limited by a sole reliance on the video image, because a line-of-sight view is nonexistent. We wondered whether this special design of the GVL might actually hinder accomplishment of intubation as a central purpose of the device.Three steps are necessary for a successful intubation with the GVL: laryngoscope insertion and glottic visualization, delivery of the styletted endotracheal tube (s-ETT) in front of the GVL camera, and guidance of the disengaged endotracheal tube (d-ETT) through the glottis and into the trachea. As described in the operator's manual, the GVL is inserted down the midline of the tongue and can be used as either a curved blade (Macintosh style) or a straight blade (Miller style). We noticed that some novice intubators actually lever the laryngoscope and halt its advancement as soon as they obtain a glottic view, which can ensue before the tip of the laryngoscope reaches the vallecula. Others insert the GVL too quickly and too deeply and obtain either a close glottic view or an esophageal view. Retracting the GVL from the esophagus provides a close glottic view. The operators' manual states, “maximum laryngeal exposure may not facilitate intubation.”1This is contrary to usual attempts made by intubators to obtain the best laryngoscopic view possible. We postulated that such attempts might actually render the passage of the ETT more difficult or impossible, and we explored these observations in an airway model.We used a Laerdal airway anatomical model 252 500 on which to simulate GlideScope® laryngoscopy and tracheal intubation (figs. 1B and C). The GVL was slowly advanced down the midline of the model's tongue. The advancement was ceased at three locations: At location 1, the blade tip was at the tip of the epiglottis; at location 2, the blade tip was within the vallecula; and at location 3, the laryngoscope was behind (posterior to) the epiglottis (figs. 2A–C, main panels). The initial position of the laryngoscope at each location was adjusted to give a view of only the arytenoids, grade 2b laryngoscopic view5(figs. 2A–C, accessory panels in the upper right corner). After performance of tracheal intubation with this initial laryngoscopic view, the GVL position was modified twice at each location. The laryngoscope was lifted first, and the trachea was intubated. The laryngoscope was then levered, with the distal end pointing up, and the trachea was intubated. The same course of action was followed at locations 1, 2 (figs. 3A and B), and 3. We performed the whole process of nine intubations twice: the first time using a recommended 60° stylet angle1and the second time using a 90° stylet angle.6A lubricated 5.5-mm s-ETT was used to minimize adhesion between the ETT and the model structures. The ETT was loaded on a malleable stylet with the ETT bevel facing to the left for all intubations. The intubator's hands maneuvering the laryngoscope and the s-ETT were recorded using a camcorder, while the passage of the d-ETT through the glottis was captured from the GVL video output (figs. 2 and 3, main panels and accessory panels, respectively). These two videos were synchronized and processed using video editing software (Adobe Premiere Pro 1.5; Adobe Systems Inc., San Jose, CA). Two compiled videos were then reviewed simultaneously.Because of softness of the tongue, lifting the laryngoscope at location 1 misdirected the camera axis from the arytenoids toward the vallecula, shifting the view from grade 2b to grade 3. Gentle lifting of the GVL at locations 2 and 3 enhanced the laryngoscopic view from grade 2b to grade 2a. Levering the GVL pointed the camera axis upward as to provide visualization of the anterior portion of the glottis (fig. 3B). During this phase, the intubator purposefully avoided lifting the laryngoscope to avoid lifting the glottic structures. Extreme levering of the laryngoscope provided a grade 1 view at locations 1 and 2. The position of the camera close up to the glottis prevented visualization of the most anterior glottic portion at location 3. Insertion of the s-ETT and advancement of the d-ETT was easier and quicker at location 2 than at locations 1 and 3. Advancement of the d-ETT was easier and time to intubation was shorter using the 60° stylet angle than the 90° stylet angle.The GVL gently lifted within the vallecula provided a grade 2a laryngoscopic view and yielded the smoothest and quickest intubation using the 60° stylet angle. Adequate room for delivery of the s-ETT, optimal alignment of the camera axis with the laryngotracheal axis, and decreased impact of the d-ETT tip with the anterior tracheal wall are the most probable explanations (fig. 3A). The Miller-style placement of the GVL resulted in a close glottic view but reduced the space between the GVL camera and the glottis for the s-ETT insertion. We recommend the Miller-style use of the GVL only if the best laryngoscopic view with the Macintosh style is a grade 3 view. Levering the GVL shifts the proximal end of the laryngoscope down and brings more bulk of the GVL blade into the oropharynx. That will severely reduce the space available to pass the ETT, especially if intubators attempt to pass the s-ETT underneath the scope. Levering the GVL also produces upward orientation of the camera portion of the blade such that the d-ETT that is passed alongside the blade easily gets hung up on the anterior commissure or cricoid or tracheal cartilages (fig. 3B). In either case, although the view is improved, accessing the laryngeal inlet and advancing the tube may be more complicated, resulting in failed intubations.In conclusion, several considerations support our suggestion that maneuvers necessary to achieve a grade 1 laryngoscopic view may render intubation with the GVL more difficult. We believe that a grade 2a view with the blade lifted within the vallecula is preferable for intubation with this device. It provides the adequate space in the oropharynx and in the immediate glottic area for the s-ETT insertion as well as optimal alignment of the camera axis with the laryngotracheal axis for ETT advancement.The use of an open airway model does not, of course, completely model the challenges of tracheal intubation in patients. However, the use of the open model allowed us to visibly demonstrate both good and bad laryngoscopic maneuvers and their corresponding glottic views. We hope that this letter may bring forth more understanding to GVL users about proper laryngoscopic and intubating maneuvers and may guide them to more intubation success with the device.†University of Rochester School of Medicine, Rochester, New York. mirsad_dupanovic@urmc.rochester.edu

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