Primus Inter Pares? The Angle of View Varies

Arguing the value of video laryngoscopy (VL) nowadays is like preaching to the choir. In the decade that followed the original publications by Kaplan et al.,1 Agrò et al.,2 and Cooper,3 we have learned a great deal about important VL advantages such as not needing to align optical and intubation axes for gentler laryngoscopy, superior glottic visualization assured by a wide angle of view “around the corner,” improved handling of blood and secretions, and the ability to obtain an intelligent assistance during tracheal intubation.4–9 Recent findings support the ease of use and increased success rate of VL compared with direct laryngoscopy (DL) in patients with an anticipated and unanticipated difficult airway,10–19 and the American Society of Anesthesiologists Task Force on Management of the Difficult Airway recommends VL as an initial approach to intubation.20 The 2013 survey of the Canadian anesthesia practice has listed VL as the top technique to use during difficult intubation.21 Moreover, a few randomized and adequately powered trials have suggested that an acute-angle (“true”) VL may be ready to successfully encroach on the “holy grail” of difficult airway management, awake flexible fiberoptic intubation.22,23 However, what remains largely unknown is whether different VL systems perform comparably in difficult airway situations. In the current issue of Anesthesia & Analgesia, Aziz et al.,24 for the first time, provide some answers to this important question. The authors report the results of a well-designed, multicenter, prospective, randomized, noninferiority trial comparing intubation success rates for the C-MAC D-blade (DB; Karl Storz, Tuttlingen, Germany) and the “gold standard” Glidescope video laryngoscope (GVL; Verathon Inc., Bothell, WA) in 1100 patients with an anticipated difficult airway. This riveting study has shown that in diverse provider and patient populations, the DB did not achieve noninferiority for the first-pass intubation, which was the primary outcome measure. Overall, both VL systems were remarkably effective, demonstrating a similar, approximately 98.5% success rate after several intubation attempts. Is the observed small difference in first-pass success rate (93% DB vs 96% GVL) a fluke or does the “Glide” live up to its name, navigating the difficult airway to safety better? Answering this question is very important for at least 2 reasons. First and foremost, a true difference demonstrated in such a large randomized prospective trial may help guide a clinician’s selection of the most effective VL device and also to better focus on personnel training and hospital resources. The true absolute 3% difference between the DB and GVL may seem small and not clinically relevant until one considers the expected 0.4% population incidence of combined difficulty with DL and mask ventilation,25 which would translate into at least 80,000 patients at risk for major airway-related complications annually in the United States alone.b Second, noninferiority trials carry a danger of “technocreep,”26 where a new benchmark is established every time noninferiority of the tested device is confirmed. Over time, the cumulative effect of noninferiority margins moves the data points farther away from the original gold standard, potentially leading to acceptance of devices with little or no efficacy. The DB performed not noninferior to the GVL on the first intubation attempt across many subgroup analyses, including different institutions and patients with multiple predictors of a difficult DL. This suggests that the observed difference in clinical performance is real. Can this be explained by the device’s technical characteristics? Does the VL angle of view matter? A Cormack–Lehane grade 1 laryngeal view was more readily achieved with the DB in the study by Aziz et al.24 This can be explained by a very distal DB camera positioning and its wider vertical field of view (60° DB vs 40° GVL #4 blade used in this study).c,27,28 However, successful VL intubation requires obtaining not only a good angle of view, but also skillful navigation of the endotracheal tube (ETT) toward and into the glottic opening. To that end, the GVL group may have demonstrated superior ETT maneuverability because of a wider panoramic angle of view produced by a steeper GVL blade angulation (60° GVL vs 40° DB) and placement of a GVL video camera farther away from the tip of the blade.4,17,27,28 However, the time to successful intubation during the first attempt did not differ between the devices.24 Moreover, noninferiority of the DB for first-pass success rate was confirmed for the attending anesthesiologists (98% DB vs 94% GVL),24 casting further doubt on the device’s design as a sole explanation for the observed difference in performance. According to the authors,24 provider bias could not be excluded fully in this study, because the DB was introduced into anesthesia practice only recently. With >360 laryngoscopists participating, it is likely that many were less clinically experienced with the DB despite preceding didactic teaching and mannequin training. A recent study by Cortellazzi et al.29 suggests that although intuitive, acute-angle VL is a complex skill requiring extensive training and practice: >70 GVL patient intubations may be required to achieve sufficient competency. The learning curve for achieving clinical proficiency with the DB is unknown, but it may be comparable. Another plausible explanation for the observed difference between the DB and the GVL may be related to procedural (intubation) bias instigated by the study design. As mentioned by the authors,24 the Gliderite® GVL stylet (Verathon Inc., Bothell, WA) was used for all tracheal intubations, which may have favored ETT delivery in the GVL group. The optimal ETT stylet configuration for the DB has not been formally investigated. Shall we embrace the GVL as an outright winner between 2 very popular acute-angle VL systems based on the results of this study? It depends on your angle of view, but a broader look at the results suggests that this conclusion may be premature. The DB and GVL were compared before, showing similar performance,28 but the subject had never undergone such rigorous examination as it did under the study by Aziz et al.24 It is difficult to reconcile the conflicting findings of the DB–GVL first-pass success rate difference with noninferiority for attending anesthesiologists and the overall intubation success rate observed by the authors. However, Aziz et al.24 should be commended for performing a well-designed, large prospective trial that produced many outstanding findings immediately applicable to clinical practice. On the basis of the study results, we can expect acute-angle VL to be highly successful in many settings of an anticipated difficult airway and confidently use it as the primary approach to difficult intubation. Furthermore, the overall effectiveness of VL in this setting was 99%, accounting for an additional 5 VL rescue intubations when the primary study device had failed (VL rescue devices were not specified by the authors).24 Because the rescue strategies were not standardized in the study protocol, one may wonder whether an overall 100% success rate could have been readily achieved if alternative VL techniques were used in all 18 patients who had failed the DB and GVL intubations. Those who like to practice evidence-based medicine, like yours truly, will find the results of this study very satisfying. The acute-angle VL “die-hards” can take a deep breath and rest their case, yet keeping in mind a true 1% risk of palatopharyngeal injury, well documented in this trial.24 The DL proponents will have to go back to the drawing board, and there are many such proponents indeed! A recent survey of Danish anesthesia departments30 has shown that almost half of the patients with an anticipated difficult airway and >40% of patients with both an anticipated difficult DL and mask ventilation are still managed by DL as a primary approach. There is a good reason to believe that such practice is widespread and spans across the operating room, emergency department, and critical care settings.31,32 With the paradigm shift in difficult airway management still in flux, we have to do a better job in educating physicians about the value of VL. Arguably the most revolutionary advance in airway management since the introduction of the laryngeal mask airway (LMA) into clinical anesthesia practice in 1983 by Brain,33 VL has now firmly staked its place not only as an alternative, but as a superior substitute to an anticipated difficult DL. Still, we have much to learn from the LMA story. We tend to be overly slow and conservative! It took almost 30 years for us to start understanding some of the true predictors of difficult LMA placement34–36 and approximately 15 years to fully appreciate the superiority of second-generation supraglottic airway devices.31,37 It has taken us a decade to learn with a high degree of certainty how effective VL could be in anticipated difficult airway…are we on an accelerated schedule? We are clearly not doing well enough. The evaluation process for the new VL devices must be streamlined from bench testing on standardized, high-fidelity airway mannequins to rigorous pilot studies and further followed by priority large prospective, controlled, multicenter trials with shared electronic databases and a dedicated data management group.24,38,39 I share the authors’ sentiment that the main results of their trial were largely unexpected. Unexpected results merit scrutiny, which helps guide future studies. New investigations should continue to systematically address the performance of mainstream nonchanneled and channeled VL devices, such as Pentax Airway Scope (Pentax Corporation, Tokyo, Japan), and Airtraq (PRODOL MEDITEC SA, Bilbao, Spain) in homogeneous patient populations and providers whose competency is standardized. Future trials would particularly benefit from head-to-head comparison of different VL systems for the situations when a difficult VL may be expected such as in patients with neck pathology, abnormal neck anatomy, decreased cervical spine motion, decreased oral entry, and in patients with restricted oropharyngeal space.12,13,18,40–43 Defining such performance will provide an ultimate angle of view to the problem. DISCLOSURES Name: Vladimir Nekhendzy, MD. Contribution: This author wrote the manuscript. Attestation: Vladimir Nekhendzy approved the final manuscript. This manuscript was handled by: Maxime Cannesson, MD, PhD.

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