Battle of the Blades: The Death of DL?

Battle of the Blades: The Death of DL? 690 539 Richie Cunningham

“I will unequivocally state that it is wrong for people to practice direct laryngoscopy in 2012.” 

— Ron Walls on EMRAP September 2012

Awfully harsh words from the man who wrote the book on emergency airway management. 8 years later, direct laryngoscopy is still widely practiced in Emergency Departments, however in some centers, video laryngoscopy is now the most commonly used device. (1) Is it just a matter of time before direct laryngoscopy is considered as outdated and crude of a device as Ron Walls claimed in his infamous appearance on EMRAP in 2012? Does video laryngoscopy have the potential to become the be-all and end-all of emergency airway management? In this four part series, we’ll consider these questions and show how in many ways this debate is easily oversimplified, and in some ways, kind of pointless.

Part 1: Trends in Laryngoscopy

First let’s take a look at Ron Walls’ own data. In the NEAR III dataset published in Annals of Emergency Medicine in 2015 (2), we can see that video laryngoscopy has been steadily rising since its introduction in the earlier 2000s. During the study period from 2002 to 2012, DL remained the device of choice in 84% of intubations. A CMAC laryngoscope was used overall 6.1% of the time and a GlideScope in just 3.2%. However, the trend in laryngoscope choice shows a much different story. 

You can see below a dramatic increase in video laryngoscopy and corresponding decrease in direct laryngoscopy after 2008. Most of this trend is due to the increase in use of the CMAC. In the first three years of the study (right around when the first video laryngoscopes were released), VL was used as the initial device in less than 1% of all intubations. By the end of the study period, DL was the initial device in 55% of all intubations and VL was used in 39% of all first attempts. 

Now if video laryngoscopy were the clearly superior device, we would expect to see an equally dramatic increase in first-pass success (FPS) along with the increasing adoption of video laryngoscopy as the blade of choice. However, that is not quite the case…

NEAR III shows us that emergency physicians are highly successful at airway management. Overall first-pass success was 83%, and the airway was ultimately secured in 99.4% of all intubation attempts. FPS starts to rise after 2004 (right around the time VL use begins to increase). However, after 2007 FPS levels off, and actually drops in the last year of the study. As you can see above, the rate of VL use begins to dramatically rise after 2008, without a corresponding increase in first pass success. Curious…

Next, let’s break down our first pass success by device. In the table below, we do see that the CMAC has the highest first-pass success among all methods (91%), however GlideScope actually shows a lower FPS (80%) than both the CMAC and DL (84%). 

Finally, we should acknowledge that this is observational data. Confounders abound. Principal among them is that the study includes the period where video laryngoscopy was just beginning to be adopted. The CMAC has a Macintosh or “standard-geometry” blade and therefore uses the same technique as standard direct laryngoscopy, and prior to the early 2000s, that’s essentially all that most EPs knew and taught each other. As the CMAC is known to increase Cormack-Lehane view (3), it figures that it would lead to increased success compared to DL.

In contrast, the GlideScope was introduced as a hyperangulated blade and its name is nearly synonymous with such, despite it now featuring a Macintosh option. It is a separate technique than both DL and the CMAC (a completely new skill for most EPs at the time of its introduction), therefore biasing it toward a lower FPS. In addition, a degree of selection bias is likely involved, as the GlideScope is often thought of as a “difficult airway tool.” 

While this may explain some of the discrepancy between FPS among CMACs, GlideScopes and direct laryngoscopes, it still doesn’t account for the lack of increasing first-pass success with the wider adoption of video laryngoscopy overall. To see which device is truly superior, we turn to two of the “highest” forms of evidence, the meta analysis and systematic review, in our next post. 

One more question to consider:

What were the individual trends in the success rates of direct laryngoscopy, the CMAC and the Glidescope (this data not available in the original paper)?

  • Increased use of VL (particularly the GlideScope) may decrease competence and ultimately FPS with DL; more on this later
  • GlideScope use never surpassed 10% of all intubations; with increased use would FPS with this specific device increase?

Take Home Points:

  1. With increased use of video laryngoscopy there was an initial rise in first-pass success in emergency department intubations
  2. VL use has continued to increase without a corresponding rise in FPS
  3. The CMAC had higher FPS than direct laryngoscopy, and the GlideScope had the lowest FPS, possibly due to lack of familiarity with the device and selection bias

Peer Reviewed by: Jon Kelley, DO, Brendan Tarzia, DO

Read Part 2 here.

References:

  1. April MD, Schauer SG, Brown Rd CA, Ng PC, Fernandez J, Fantegrossi AE, Maddry JK, Summers S, Sessions DJ, Barnwell RM, Antonacci M. A 12-month descriptive analysis of emergency intubations at Brooke Army Medical Center: a National Emergency Airway Registry study. US Army Med Dep J. 2017 Oct-Dec;(3-17):98-104. PMID: 29214627.
  2. Brown 3rd CA, Bair AE, Pallin DJ, Walls RM, NI Investigators. Techniques, success, and adverse events of emergency department adult intubations. Ann Emerg Med 2015;65:363–70, e1.
  3. Brown 3rd CA, Bair AE, Pallin DJ, Laurin EG, Walls RM, National Emergency Airway Registry Investigators. Improved glottic exposure with theVideo Macintosh Laryngoscope in adult emergency department tracheal intubations. Ann Emerg Med 2010;56:83–8.