The development of direct laryngoscopy

Trends in Anaesthesia and Critical Care 4 (2014) 3e9

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REVIEW

The development of direct laryngoscopy Erol Cavus*, Volker Dörges The Department of Anaesthesiology and Intensive Care Medicine, University Hospital Schleswig-Holstein, Campus Kiel, Schwanenweg 21, D-24105 Kiel, Germany

s u m m a r y Keywords: Airway management Intubation Difficult airway Videolaryngoscopy

The use of direct laryngoscopy for endotracheal intubation is one of the key skills of anaesthesiologists and every physician involved in airway management. Direct laryngoscopy confers the known advantages of familiarity, direct glottic visualisation, cost effectiveness, equipment availability, and a steep learning curve. However, the prevalence of insufficient views of the glottis is persistent. Therefore, alternative intubation techniques should be available in such a crucial situation, including indirect laryngoscopic techniques such as videolaryngoscopy. Current videolaryngoscopes play an important role in the management of an unexpected difficult airway. Additionally, the use of a videolaryngoscope may be considered in a predicted difficult airway, if mask ventilation and oxygenation can be warranted. However, it is important to know that today videolaryngoscopes do not build a homogeneous class; moreover, they differ in design, technical configuration, monitor type and, most importantly, in blade type, so that the user has to become familiar with each device before they are used in an emergency situation. Therefore, the greatest benefit from videolaryngoscopy may be obtained, if it is used routinely in elective cases to become familiar with the device outside of a difficult intubation situation. In this case, videolaryngoscopy has the potential to save time and decrease-patient morbidity. This review addresses actual videolaryngoscopy techniques and their use in both clinical and pre-hospital airway management scenarios. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction

of the devices were greatly improved. This resulted in a wide distribution of videolaryngoscopes, which became a standard procedure for patients with known or suspected difficult airway. Nevertheless, it is important to know that today videolaryngoscopes do not build a homogeneous class; moreover, they differ in design, technical configuration, monitor type and, most importantly, in blade type, so that the user has to become familiar with each device before they are used in an emergency situation.4,5 Therefore, it may take some more time before the best videolaryngoscopic system could be identified that may also become a standard for routine intubations.

Use of the videotechnique in addition to conventional laryngoscopy for both teaching routine laryngoscopy for endotracheal intubation and for managing a difficult airway has been known for more than 15 years. In the beginning, optical image guides and video cameras had been integrated into standard laryngoscopes, so that a magnified and detailed view could be displayed on an external monitor whilst conventional direct laryngoscopy was performed. Later on, this principle was advanced and resulted in laryngoscopes with differing shapes and integrated rigid or flexible fibreoptics, such as the WuScope,1 Bullard,2 and UpsherScope.3 However, the past decade has witnessed some important developments in direct and indirect laryngoscopy, which were based on innovations in the field of video-assisted airway management. With the miniaturisation of optical cameras and liquid crystal displays (LCD), and the development of light sources with lightemitting-diodes (LED), optical quality, handling, and mobility

* Corresponding author. Tel.: þ49 431597 2991; fax: þ49 431597 3002. E-mail address: [email protected] (E. Cavus). 2210-8440/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tacc.2013.08.001

2. Classification of videolaryngoscopes The main difference in videolaryngoscopes arises from the type of blade that is incorporated into the system. Videolaryngoscopes that are based on a conventional blade shape, such as the Macintosh or Miller blade, allow direct visualisation of the glottic entrance by direct laryngoscopy in addition to the video view. As a side-effect, the user is familiar with the handling of these conventional blade types. Alternatively, videolaryngoscopes with highly-curved or angulated blades are available that allow an

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increased “look around the corner” to the glottic entrance. On the one hand, these videolaryngoscopes mostly allow the best visualisation of the glottis; on the other hand, generally, they provide obligatory indirect visualisation (no direct view of the glottic entrance possible; Fig. 1); further, due to the high blade angulation, the use of a malleable or rigid tube stylet is mandatory in nearly all cases. The user has to learn that intubation difficulties have moved from the impaired visualisation process to difficult tube advancement. Despite optimal glottic visualisation, the most difficult part now with indirect videolaryngoscopy is to enter the curved tube into the glottic entrance and to advance it into the trachea.5 Some obligatory indirect laryngoscopes come with a tubeguiding channel that is incorporated in the curved blade. Therefore, the use of a tube stylet to guide the tube to the glottic entrance is not mandatory; however, generally it also does not allow for a correction in the direction of the tube. For hygienic purposes all videolaryngoscopic systems are available as a disposable variant. Compared to the reusable steelmade types which have lower blade profiles, the disposable versions are mainly made from plastic materials and have larger (thicker) blade profiles. Finally, videolaryngoscopes are available with external and integrated monitors. External monitors have the advantage that they provide optimal visualisation of the intubation process for the whole team, which may anticipate actions such as extralaryngeal manipulations or suctioning. Additionally, recording options for images and videos are available. In contrast, the smaller integrated monitors offer the greatest mobility for videolaryngoscopy with minimal place requirement, which will only be improved once wireless technology has been implemented. Furthermore, these smaller systems are predominantly available at affordable prices. This emphasises their use in the emergency setting, e.g. in-hospital or pre-hospital emergency medicine. Since all devices are battery operated, great attention must be paid to the battery capacity to avoid a system blackout in the sensible phase of intubation. 3. Technique of videolaryngoscopy (VLS) Videolaryngoscopes provide a “look around the corner” to achieve optimal visualisation of the glottis without further manipulation of the patient (e.g. flexion or extension of the cervical spine), and without the need for alignment of the oro-pharyngolaryngeal axis. However, the higher the curvature of the blade is, the more the chance to perform direct laryngoscopy is reduced; in this case tracheal intubation has to be done obligatory with indirect visualisation. Furthermore, to follow the high curvature of the blade with the endotracheal tube, a tube-guide/malleable stylet is necessary.6,7 Additionally, injuries of pharyngeal structures with the use of videolaryngoscopes have been described, if advancement

C-MAC #3 (direct view)

of the styletted endotracheal tube around the tongue is not directly observed, until it becomes visible on the monitor.8,9 Compared with conventional direct laryngoscopy, videolaryngoscopy may result in a reduced pressure on the maxillary teeth.4 4. Use of videolaryngoscopy 4.1. Clinical use Exemplarily, clinical investigations of the most studied videolaryngoscopes C-MAC (Karl Storz, Tuttlingen, Germany; Fig. 2), GlideScope (Verathon Medical, Bothell, WA, USA; Fig. 3), McGrath Series 5 videolaryngoscope (Aircraft Medical, Edinburgh, United Kingdom; Fig. 4), Truview (Truphatek International Limited, Netanya, Israel; Fig. 5), and Pentax-AWS-S100 (Pentax Medical; distributed by Ambu Inc.; Fig. 6) are mentioned. Several authors were able to show superior visualisation of the glottis with the classical C-MAC compared to conventional direct laryngoscopy.10e13 Aziz et al. compared the C-MAC with direct laryngoscopy (all using Macintosh blades sizes 3 or 4) in a singlecentre study in 296 patients with a predicted difficult airway. They reported significantly improved glottis visualisation (CormackeLehane) and higher first-attempt intubation success with the use of videolaryngoscopy. As with all videolaryngoscopes, time to intubation was longer with C-MAC videolaryngoscopy than with direct laryngoscopy (successful attempts).13 Even if the application of a stylet cannot be eliminated completely, most intubations using a C-MAC videolaryngoscope can be performed without stylet use.6,7 In a preliminary study by Cavus et al. in patients, in whom conventional Macintosh laryngoscopy failed, the use of the curved CMAC D-Blade provided better glottic visualisation and intubation success in all patients.14 The GlideScope is the prototype of modern obligate indirect videolaryngoscopes and many studies have been published regarding its use in the OR,15e19 in normal and difficult intubation scenarios,20e26 and in comparison to other videolaryngoscopes.6,12,27e33 Use of the GlideScope resulted in improved glottic visualisation according to Cormack and Lehane in most patients,34 and improvement of intubation success in difficult airways.24,35 Recently, Aziz and colleagues analysed 2.004 GlideScope intubations and reported an overall intubation success rate of 97%. Conversely, 3% could not be intubated with the GlideScope; the authors concluded that maintenance of competency with alternate methods of intubation is mandatory.26 Compared to conventional laryngoscopy with a Macintosh blade, the glottic view may be improved by use of the Truview videolaryngoscope.28,36,37 Also, it may result in a higher intubation success rate in difficult airway situations,38 but in comparable intubation success rates in normal airways; however, airway morbidity related to laryngoscopy may be lower.36 As known from

C-MAC #3 (indirect view)

C-MAC D-Blade (obligate indirect view)

Fig. 1. Main differences in sight between Macintosh- and highly-curved blade videolaryngoscopes. Left: Macintosh blade with the option for direct laryngoscopy; Centre: Macintosh blade with the option for indirect (video-)laryngoscopy; Right: Highly-curved blade with the option for only indirect (video-)laryngoscopy.

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Fig. 2. C-MAC videolaryngoscope (Karl Storz, Tuttlingen, Germany) with Macintosh blade and portable external monitor. (Picture: Erol Cavus, Kiel, Germany).

all VLS, intubation with the Truview may take longer.36 However, in patients with cervical spine immobilisation, Malik and colleagues experienced inferior visualisation and intubation success compared to other VLSs.28 One of the first fully portable devices with higher blade angulation and an integrated monitor is the McGrath Series 5 videolaryngoscope. Most clinical data show improved visualisation and

Fig. 4. McGrath Series 5 videolaryngoscope (Aircraft Medical, Edinburgh, United Kingdom). (Picture: Rüdiger Noppens, Mainz, Germany).

intubation success compared to conventional laryngoscopy with both Macintosh39e41 and Henderson straight42 blades. Due to the curved blade shape, advancement of the styletted tube cannot directly be observed; therefore, caution is needed during advancement of the tube to avoid injuries.9 A recent study by Ng and colleagues compared the McGrath Series 5 with the C-MAC videolaryngoscope.43 Despite an inferior C/L grading, the authors

Fig. 3. GlideScope videolaryngoscope (Verathon Medical, Bothell, WA, USA) with single-use blade technique (Cobalt) and portable external (AVL) monitor. (Picture: Erol Cavus, Kiel, Germany).

Fig. 5. Truview videolaryngoscopy system (Truphatek International Limited, Netanya, Israel) with different blade sizes. (Picture: Richard Schalk, Frankfurt, Germany).

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perform the intubation. However, since employment of some devices varies significantly, and often simply obligate indirect laryngoscopy is possible, only a limited number of VLSs may be used as an intubation trainer for conventional laryngoscopy and intubation. VLSs based on Macintosh blades offer the possibility for conventional direct laryngoscopy attempts by the student, whereas at the same time, the instructor is able to analyse the airway and the trainee’s intubation attempt on the monitor.49 A study using the V-MAC videolaryngoscope (a precursor of the Storz C-MAC) for guidance of the instructors’ feedback in the clinical setting showed an increase in the trainee success rate for intubation and a decreased rate of oesophageal intubations compared to instructor assistance based on standard cues.50 In the absence of a videolaryngoscope, the faculty member is more likely to take over the procedure earlier if a problem is encountered, thereby reducing the experience afforded to the trainee. In a study by Carlino and colleagues using the Truview as a teaching tool for young anaesthesia residents, intubation success after the first attempt was nearly doubled compared to conventional Macintosh laryngoscopy.51 The demands for adequate clinical experience with airway management are increasing in training programs. The environment providing acute airway management is often accomplished in the setting of high stress; therefore, allowing the trainee to manage the airway, is a crucial decision that is made by the faculty member. 4.3. Difficult airway

Fig. 6. Pentax-AWS-S100 videolaryngoscope (Pentax Medical; distributed by Ambu Inc.). (Picture: Rüdiger Noppens, Mainz, Germany).

found a significantly faster intubation time, fewer intubation attempts, and an easier device handling of the C-MAC in patients with poor Mallampati scores, compared with the McGrath videolaryngoscope. The McGrath videolaryngoscope is also available with a disposable Macintosh blade type, and most recently, interchangeable with a disposable curved blade (x-Blade); however, there are no published clinical data concerning the use of these new devices. Another videolaryngoscope with a highly-curved blade, but with an additional guiding channel is the Pentax-AWS-S100 that has shown superiority with regard to glottic visualisation and intubation success in the difficult airway over conventional laryngoscopy in patients with immobilisation of the cervical spine.28,44 Conversely, in a recent study of morbidly obese patients, Abdallah and colleagues showed faster intubation and higher first pass success rates with a conventional size 4 Macintosh blade, compared with the Pentax-AWS, despite inferior glottic visualisation.45 Particularly in morbidly obese patients the relatively bulky design of channelled blades may cause difficulties during insertion into the mouth.46 Problems with the guiding channel may arise if a fixed rotation of the cervical spine is present,47 or if otherwise the tube may not be redirected from the channel.48 4.2. Education All VLSs provide optimal visualisation of the glottis on a video screen. Even if the screen sizes differ, they may all be used as teaching tools in the way of a “what to see during intubation” tutorial. The use of videolaryngoscopy allows the supervising faculty member to directly observe the actions of the trainee, thereby reducing the anxiety associated with allowing the trainee to

Previously, the use of videolaryngoscopy for managing the unexpected difficult airway was limited by restricted mobility and extended preparation time. The current videolaryngoscopes available are so mobile and quick to set up that this is not an issue anymore. Serocki and colleagues found that VLS was very helpful in many clinical conditions of an expected difficult airway, including limited neck mobility, reduced thyromental distance, reduced inter-incisor distance or retrognathia.24 Their data confirmed that both the videolaryngoscope with a Macintosh blade (DCI V-MAC) and the highly-curved GlideScope enhanced glottic visualisation in patients with difficult conventional laryngoscopy. More recently, the same authors compared two obligate indirect laryngoscopes, the C-MAC D-Blade and the GlideScope, with conventional Macintosh laryngoscopy in a set of patients scheduled for ENT surgery. Laryngeal view was greatly improved with VLS. Most importantly, they found that in patients with worse laryngeal view with conventional direct laryngoscopy (CormackeLehane C/L 3 or 4), glottis view was improved to C/L 1 or 2 in all patients using VLS. If intubation with direct laryngoscopy was successful, it was significantly faster and needed less attempts than VLS; however, 13% of patients (n ¼ 4) could not be intubated by conventional direct laryngoscopy, but could be successfully intubated by VLS on the first attempt. The use of either videolaryngoscope (C-MAC DBlade and GlideScope, respectively) resulted in 100% intubation success.52 Videolaryngoscopy cannot and should not replace awake fibreoptic intubation in many cases of a predictable difficult airway. Nonetheless, in an expected difficult airway, VLS may be a worthy addition as an awake intubation technique.53e55 Although the 2013 ASA guidelines highlight the approach of awake intubation as the preferred method to manage expected difficult airways, consideration of videolaryngoscopy under general anaesthesia may be investigated as the primary method for intubation if difficulty with intubation, but not mask ventilation is expected. Consequently, video-assisted laryngoscopy has been added as one of four basic management choices for management of the difficult airway.56

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VLS has successfully been applied for the management of the difficult airway in ENT and maxillofacial surgery,24 neurosurgery,57 obstetrics,58 traumatology, paediatrics,59 the intensive care unit,60 the emergency department,61 and in physician-based out-of-hospital emergency medicine.62 4.4. Obstetrics Aziz et al. reported retrospectively on the use of the GlideScope videolaryngoscope on patients in an obstetric unit.63 In 18 of 180 patients that had endotracheal intubation for a caesarean section, the GlideScope was used primarily, and in one patient as a rescue device after failed direct laryngoscopy. Though 16 of 18 patients had predictors of a difficult airway, all patients could successfully be intubated with VLS on the first attempt, compared to 157 of 162 patients with direct laryngoscopy. 4.5. Intensive care medicine In a recent study, the GlideScope videolaryngoscope was used by less experienced operators for the initial intubation attempt on an intensive care unit. In comparison to historical data of conventional laryngoscopy, the use of the VLS improved first-attempt success from 68% to 91%, and reduced the number of cases with more than 3 attempts from 20% to 4%, and oesophageal intubations from 14% to 0%, respectively. The authors concluded that VLS should be used as the primary device when urgent intubations are performed by less experienced operators.64 Other study groups also investigated the use of the GlideScope videolaryngoscope in critically ill patients. They also found better glottis visualisation with VLS compared to conventional direct laryngoscopy; however, intubating time with the GlideScope VLS was longer, resulting in more hypoxaemic patients, so that the overall outcome was not positively influenced by the use of the VLS.65,66 The prolongation of intubation time, depending on the kind of VLS used, is a known issue6; however, it develops the highest relevance in critically ill patients with existing limited respiratory reserve. Particularly in the intensive care setting, it may become necessary to change to a different sized endotracheal tube, or from an orotracheal to a nasotracheal route. Airway exchange catheters can reduce the incidence of re-intubation failure, which can be further improved by the use of such catheters under videolaryngoscopic vision.60,67 A case report demonstrated the use of VLS to exchange a Combitube, which was placed by paramedics after failed direct vision laryngoscopy and intubation, for an endotracheal tube to establish a definitive airway.68 It is a common pathway to use an extraglottic airway device such as a laryngeal mask, laryngeal tube, or Combitube in the pre-hospital setting if the patient’s airway is difficult and direct laryngoscopy is unsuccessful. Thus, exchanging this device for an endotracheal tube may be extremely difficult. 4.6. Emergency use (pre-hospital, in-hospital, Emergency Department (ED)) Limited data is available concerning the use of VLS in the out-ofhospital setting. Many studies simulate emergency conditions using intubation on a manikin,33,69e73 such as cervical immobilisation, limited access to the patient’s head, and cardiopulmonary resuscitation. Most of the data shows superiority of VLS over conventional direct laryngoscopy regarding glottis visualisation and intubation success. Depending on the local Emergency Medical System (EMS), VLS was used in patients by Paramedics or Emergency Physicians. Further, emergency intubations in the Emergency Department (ED)

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may be summarised in this category. As is also known from the clinical setting, use of the GlideScope Ranger in an emergency setting improved glottic visualisation and reduced the number of intubation attempts, as compared to conventional laryngoscopy.35,74 Wayne et al. reported on the use of the portable GlideScope Ranger in 315 pre-hospital intubations performed by paramedics.75 Intubation success rate was only slightly improved from 95% to 97%; however, both the number of intubation attempts and intubation time were half with the GlideScope Ranger. In a retrospective, observational study by Struck et al., the GlideScope Ranger videolaryngoscope was used in 23 patients by anaesthetists in a Helicopter Emergency Medical Service (HEMS). All patients could be intubated successfully, including eight patients, in whom previous conventional laryngoscopy attempts by the ground crews had failed.74 However, Choi and colleagues showed some cases of unsuccessful intubation with the GlideScope Ranger despite excellent visualisation, which highlights the need for training on the device outside of an emergency situation.61 Noppens et al. reported on the successful use of the McGrath Series 5 VLS in a patient with traumatic brain injury and cervical immobilisation. Since mouth opening and subsequently glottis view with a cervical collar in place is significantly reduced, the use of a videolaryngoscope may help to facilitate endotracheal intubation. Additionally, cervical spine movement may be reduced with the use of an indirect laryngoscopy technique.76 In an observational study, Cavus et al. described the use of the C-MAC (Macintosh blade) videolaryngoscope by emergency physicians in a HEMS for intubation during trauma, cardiopulmonary resuscitation, and unconsciousness and dyspnoea of other aetiology.62 All patients could be intubated with the device; however, there were six patients in whom, although using the C-MAC videolaryngoscope, the direct laryngoscopic view instead of the videolaryngoscopic view was used because of anatomical reasons, and secretions (blood, vomit). It is important to know that a common problem of all pre-hospitally used videolaryngoscopes, requiring an LCD monitor to view the glottis, is that during daylight it may be impossible or at least difficult to see the glottis due to sunlight reflection on the monitor display. This underlines that direct laryngoscopy should always be retained as a primary skill in emergency airway management. Sakles et al. reported on the use of the C-MAC (Macintosh blade) in the emergency department. They concluded that the C-MAC provided better glottis views and higher intubation success rates, when compared to conventional direct laryngoscopy.77 The same study group investigated the GlideScope (GVL, Ranger) in the emergency department and found equivalent overall success rates compared to direct laryngoscopy. However, first-attempt success was higher with the GlideScope videolaryngoscope (75% vs. 68%).78 Compared to conventional Macintosh laryngoscopy, the optical laryngoscope Airtraq (Prodol Meditec, Guecho, Spain) that uses mirrors instead of video technology, has demonstrated promising results in patients at low79 and higher risk80 for difficult tracheal intubation, and in patients with immobilisation of the cervical spine.81 McElwain and colleagues demonstrated that the Airtraq laryngoscope performed better than the C-MAC (Macintosh blade) and conventional Macintosh laryngoscopes in patients undergoing tracheal intubation with manual in-line stabilisation of the cervical spine.82 However, more recently, Trimmel and colleagues showed that the Airtraq laryngoscope had no benefit over conventional direct laryngoscopy in the pre-hospital setting, if used by nontrained physicians, and therefore it cannot be recommended in the pre-hospital setting without significant clinical experience obtained in the operating room.83 Finally, the use of VLS has been reported anecdotally in combination with other indirect laryngoscopy techniques such as the Bonfils endoscope.84 In a case report of an emergency intubation in

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an adult patient with acute epiglottitis, VLS was successfully combined with a paediatric stylet to facilitate endotracheal intubation.85 5. Documentation Videolaryngoscopes with external monitors mainly have the capability to record and save video sequences and image captures from the video screen. This allows for the use as a teaching tool (didactic educational help and debriefing), and for documentation of correct tube position (placement) and airway pathologies. As an example, in newborns, the enlarged panoramic view and recordings of VLS assisted in the correct diagnosis of vocal cord paralysis.59 6. Summary The use of direct laryngoscopy for endotracheal intubation is one of the key skills of anaesthesiologists and every physician involved in airway management. Direct laryngoscopy confers the known advantages of familiarity, direct glottic visualisation, cost effectiveness, equipment availability, and a steep learning curve. However, despite adjunctive manoeuvres such as external laryngeal manipulation and head lift, or the use of endotracheal tube introducers or bougies, the prevalence of insufficient views of the glottis (grade 3 or 4 views at direct laryngoscopy) is persistent. Therefore, alternative intubation techniques should be available in such a crucial situation, including indirect laryngoscopic techniques such as videolaryngoscopy. Since current videolaryngoscopes are extremely mobile and quick to set up, they play an important role in the management of an unexpected difficult airway. Further, the use of a videolaryngoscope may be considered in a predicted difficult airway, if mask ventilation and oxygenation can be warranted. However, the “gold standard” for managing patients with predicted airway difficulties, when oxygenation after induction of anaesthesia presumably cannot be assured, is the use of a flexible fibreoptic or intubation endoscope in an awake, spontaneously breathing patient. It is important that the greatest benefit from VLS may be obtained, if it is used routinely on a daily basis in elective cases, and, therefore, the healthcare professional performing intubation becomes familiar with the device outside of a difficult intubation situation. In this case, VLS has the potential to save time and decrease-patient morbidity. Conversely, it will also be important for teaching programs to ensure that excellent skills in both direct laryngoscopy with different direct laryngoscopy blades (e.g. curved, straight, and levering tip) and use of flexible intubation endoscopes are still taught, obtained, and maintained. Conflict of Interest The University Hospital Schleswig-Holstein Campus Kiel, Department of Anaesthesiology and Intensive Care Medicine, or any of its employees, receive no compensation for this work. However, Volker Dörges is a member of the Karl Storz advisory board, and receives grant support from Karl Storz, Tuttlingen, Germany, for studies related to airway management. References 1. Wu TL, Chou HC. A new laryngoscope: the combination intubating device. Anesthesiology 1994;81(4):1085e7. 2. Borland LM, Casselbrant M. The Bullard laryngoscope. A new indirect oral laryngoscope (pediatric version). Anesth Analg 1990;70(1):105e8. 3. Pearce AC, Shaw S, Macklin S. Evaluation of the Upsherscope. A new rigid fibrescope. Anaesthesia 1996;51(6):561e4. 4. Lee RA, van Zundert AA, Maassen RL, Wieringa PA. Forces applied to the maxillary incisors by video laryngoscopes and the Macintosh laryngoscope. Acta Anaesthesiol Scand 2012;56(2):224e9.

5. Levitan RM, Heitz JW, Sweeney M, Cooper RM. The complexities of tracheal intubation with direct laryngoscopy and alternative intubation devices. Ann Emerg Med 2011;57(3):240e7. 6. Maassen R, Lee R, Hermans B, Marcus M, van Zundert A. A comparison of three videolaryngoscopes: the Macintosh laryngoscope blade reduces, but does not replace, routine stylet use for intubation in morbidly obese patients. Anesth Analg 2009;109(5):1560e5. 7. van Zundert A, Maassen R, Lee R, Willems R, Timmerman M, Siemonsma M, et al. A Macintosh laryngoscope blade for videolaryngoscopy reduces stylet use in patients with normal airways. Anesth Analg 2009;109(3):825e31. 8. Cooper RM. Complications associated with the use of the GlideScope videolaryngoscope. Can J Anaesth 2007;54(1):54e7. 9. Williams D, Ball DR. Palatal perforation associated with McGrath videolaryngoscope. Anaesthesia 2009;64(10):1144e5. 10. Byhahn C, Iber T, Zacharowski K, Weber CF, Ruesseler M, Schalk R, et al. Tracheal intubation using the mobile C-MAC video laryngoscope or direct laryngoscopy for patients with a simulated difficult airway. Minerva Anestesiol 2010;76(8):577e83. 11. Cavus E, Kieckhaefer J, Dörges V, Moeller T, Thee C, Wagner K. The C-MAC videolaryngoscope: first experiences with a new device for videolaryngoscopyguided intubation. Anesth Analg 2010;110(2):473e7. 12. Teoh WH, Saxena S, Shah MK, Sia AT. Comparison of three videolaryngoscopes: Pentax Airway Scope, C-MAC, Glidescope vs the Macintosh laryngoscope for tracheal intubation. Anaesthesia 2010;65(11):1126e32. 13. Aziz MF, Dillman D, Fu R, Brambrink AM. Comparative effectiveness of the CMAC video laryngoscope versus direct laryngoscopy in the setting of the predicted difficult airway. Anesthesiology 2012;116(3):629e36. 14. Cavus E, Neumann T, Dörges V, Moeller T, Scharf E, Wagner K, et al. First clinical evaluation of the C-MAC D-Blade videolaryngoscope during routine and difficult intubation. Anesth Analg 2011;112(2):382e5. 15. Cooper RM, Pacey JA, Bishop MJ, McCluskey SA. Early clinical experience with a new videolaryngoscope (GlideScope) in 728 patients. Can J Anaesth 2005;52(5): 191e8. 16. Rai MR, Dering A, Verghese C. The Glidescope system: a clinical assessment of performance. Anaesthesia 2005;60(1):60e4. 17. Sun DA, Warriner CB, Parsons DG, Klein R, Umedaly HS, Moult M. The GlideScope Video Laryngoscope: randomized clinical trial in 200 patients. Br J Anaesth 2005;94(3):381e4. 18. Teoh WH, Shah MK, Sia AT. Randomised comparison of Pentax AirwayScope and Glidescope for tracheal intubation in patients with normal airway anatomy. Anaesthesia 2009;64(10):1125e9. 19. Jones PM, Turkstra TP, Armstrong KP, Armstrong PM, Harle CC. Comparison of a single-use GlideScope Cobalt videolaryngoscope with a conventional GlideScope for orotracheal intubation. Can J Anaesth 2010;57(1):18e23. 20. Agrò F, Barzoi G, Montecchia F. 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