October 1, 2020

REBEL Cast Ep87: Video Laryngoscopy – Standard vs Hyperangulated Geometry

Background information: There are two popular blade shapes for video laryngoscopy, a standard-geometry blade comparable to a Macintosh blade and a hyperangulated blade. The standard-geometry blade permits both direct and indirect visualization during intubation, whereas the hyperangulated blade permits only indirect visualization. The hyperangulated blade is used with a rigid stylet, whereas the standard-geometry blade allows the use of a bougie if indicated.

Proposed benefits of the hyperangulated blade include decreasing the need for head and neck manipulation. Previous research includes an observational study using emergency department data that compared the two blade shapes found no association between blade geometry and first-attempt success rates (Moiser et al.), but this was a single-center study with only 463 patients. Previous unadjusted data from the registry used in the current study by Driver et al. found that standard-geometry video laryngoscopy had a higher first-attempt success rate than video laryngoscopy using the hyperangulated blade (91 percent versus 80 percent, n=1,644) based on data from 2002 through 2012 (Brown et al.).

REBEL  Cast Episode 87 –  Video Laryngoscopy – Standard vs Hyperangulated Geometry

Paper: Driver et al. Comparing Emergency Department First-Attempt Intubation Success With Standard-Geometry and Hyperangulated Video Laryngoscopes. Ann Emerg Med 2020. PMID 32362430.

Clinical QuestionWhich blade geometry for video laryngoscopy is associated with higher first-pass success rates?

What They Did:

  • Observational study using the National Emergency Airway Registry (NEAR)
    • A prospective, multicenter, international registry from the United States, Canada, and Australia of emergency department intubation data on patients (n=11,927) using video laryngoscopy with:
      • Standard-geometry (n=7,255)
        • C-MAC Macintosh blade
        • GlideScope Titanium Mac or disposable DirectView MAC blades
      • Hyperangulated-geometry (n=4,672)
        • C-MAC D-blade
        • GlideScope hyperangulated blade (LoPro and GVL)

Inclusion:

  • ≥ 14 years of age
  • Orally intubated in the emergency department at a participating site for the National Emergency Airway Registry
  • Intubated using video laryngoscopy with standard-geometry or hyperangulated blades
  • Intubated between January 1st, 2016 and December 31st, 2018

Exclusion:

  • Intubated using only topical anesthesia
  • Missing data for primary outcome or age
  • Intubated using a hyperangulated blade with tube channel
  • Study site failed to document ≥ 90 percent of intubations

Outcomes:

  • Primary: First-attempt success rate in intubation
    • Attempt = single insertion of laryngoscope blade into the mouth
  • Secondary:
    • Successful intubation without adverse events
    • Proportion of patients with Cormack-Lehane grade 1 or 2 on the 1st attempt
    • Changing the device after a failed first attempt
    • Hypoxemia
    • Lowest oxyhemoglobin saturation
    • Any adverse events (i.e. cardiac arrest, airway injury, hypoxemia, laryngoscopes failure, dental or lip trauma, and iatrogenic bleeding)

Results:

  • Included 11,927 recorded intubation encounters
    • 97.6% of standard geometry intubations performed with C-MAC and 34% with a bougie
    • 87.8% of hyperangulated geometry intubations performed with GlideScope
    • Hyperangulated geometry more frequently used for trauma and had a higher proportion of anticipated and confirmed difficult airway characteristics compared to standard geometry intubations

The above table shows unadjusted data in this study showed similar first-attempt success rates between standard-geometry versus hyperangulated blades, 91.9% and 89.2% respectively. The odds ratio for first attempt success based on laryngoscope type, standard geometry versus hyperangulated blade was 2.7 with a 95% confidence interval from 1.6 to 3.8.

Using multiple logistic regression, the results then were adjusted for possible confounders (including age, sex, obesity, medical versus traumatic indication for intubation, initial airway assessment, patient positions, use of neuromuscular blocking agent, and intubator’s experience level). After adjustment, the odds ratio for first attempt success based on laryngoscope type, standard geometry versus hyperangulated blade was 1.32 with a 95% confidence interval from 0.81 to 2.17. In the sensitivity analysis removing clustering by site, the odds ratio for first attempt success based on laryngoscope type, standard geometry versus hyperangulated blade, was 1.32 with a 95% confidence interval from 1.14 to 1.54.

Strengths:

  • This was a large, multi-center registry that permitted a large sample size (n=11,927) of video laryngoscopy with standard-geometry (n=7,255) or hyperangulated blades (n=4,672)
  • Central coordinating center screened all entries for completeness and data consistencies
  • Each study site must have completed data collection forms for at least 90% of intubations performed
  • To account for differences in patient and operator characteristics, used multiple logistic regression to account for confounders (i.e. adjusted analysis)
  • Performed 2 sensitivity analyses to determine whether site differences had a strong effect on the multivariable model results for the primary outcome

Limitations:

  • Groups not balanced at baseline. Hyperangulated group had fewer ideal conditions compared to standard geometry group:
    • More obesity
    • More trauma intubations
    • More initial impression of difficult airway
    • Less preoxygenation >3 minutes
    • Less apneic oxygenation
  • Confounding by indication: physicians may have selected a particular blade shape for unmeasured reasons
  • Did not account for intubator experience. A more meaningful variable would be the number of previous intubation attempts
  • Unclear whether intubators using standard geometry VL viewed the video screen or directly visualized the larynx directly
  • Trainees performed >90% of intubations therefore limiting generalizability to physicians with substantial intubating experience
  • This was an observational study and thus not randomized. As noted by the authors, there is the possibility that confounding variables that were addressed in the analyses affected blade selection. For example, the standard-geometry blade is popular with new trainees because it allows the experienced physician to visualize the trainee’s view while the trainee gains experience in direct laryngoscopy, but specific data beyond postgraduate year, fellow, or attending on the experience of the intubating physicians was not available 
  • Brand of the video laryngoscope was not included in the analysis, and studies on differences in brand of video laryngoscopy have shown conflicting results on whether brand affects intubation success rate
  • There was significant variability in blade geometry between sites, varying between <1% to 100% using the standard geometry blade. In the sensitivity analysis removing clustering by site, the odds ratio for first attempt success based on laryngoscope type, standard geometry versus hyperangulated blade, was 1.32 with a 95% confidence interval from 1.14 to 1.54. The odds ratio was unchanged when clustering by site was added, but the confidence interval crossed 1. This result indicates that physician familiarity with the blade shape as suggested by differences in blade geometry selection between sites may affect outcomes.

Discussion: In unadjusted analysis of previous data from the National Emergency Airway Registry, the standard-geometry video laryngoscopy had a higher first-attempt success rate than video laryngoscopy using the hyperangulated blade (91 percent versus 80 percent, n=1,644) based on data from 2002 through 2012 (Brown et al.). However, the data were unadjusted for possible confounders and included data from a time when video laryngoscopy was relatively rare, accounting for less than 1% of intubations in the first three years of data. Unadjusted data in the current study by Driver et al. showed a smaller difference in first-attempt success rates between standard-geometry versus hyperangulated blades, 91.9% and 89.2% respectively.

Overall, in this observational study, there was no difference between standard-geometry versus hyperangulated blades in first-attempt intubation success when adjusting for possible confounders. However, because each blade has theoretical benefits in different scenarios, physicians should use clinical judgment in choosing the blade if both options are available. 

Author conclusion: “In this large registry of patients intubated with video laryngoscopy in the emergency department, we observed no association between blade shape (standard-geometry versus hyperangulated laryngoscope) and first-attempt intubation success after adjusting for confounding variables.” 

Clinical take-home point: Based on this observational study in emergency intubations using video laryngoscopy, physicians may use whichever blade shape they prefer, with blade shape selection, based on the characteristics of the patient requiring intubation.

References:

  1. Driver et al. Comparing Emergency Department First-Attempt Intubation Success With Standard-Geometry and Hyperangulated Video Laryngoscopes. Ann Emerg Med 2020. PMID 32362430
  2. Brown CA et al. NEAR III Investigators. Techniques, success, and adverse events of emergency department adult intubations. Ann Emerg Med.2015. PMID 25533140
  3. Moiser J et al. A comparison of Glidescope video laryngoscope to the C-MAC video laryngoscope for intubation in the emergency department. Ann Emerg Med 2013. PMID 23374414.

For More Thoughts on This Topic, Check Out:

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

Cite this article as: Cara Borelli DO, "REBEL Cast Ep87: Video Laryngoscopy – Standard vs Hyperangulated Geometry", REBEL EM blog, October 1, 2020. Available at: https://rebelem.com/rebel-cast-ep87-video-laryngoscopy-standard-vs-hyperangulated-geometry/.
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Cara Borelli DO

Emergency Medicine Resident at University of Texas Health Science Center at San Antonio (UTHSCSA)
1 Comment
  • thomas fiero
    Posted at 04:08h, 27 October Reply

    excellent and thank you, Cara and Salim… very cool discussion/analysis.

    about a 18 months ago, maybe longer, I had just heard about the other Driver study out of Hannepin suggesting best success using a Bougie on all first attempt intubations. so I invited my boss, and another doc and a few nurses to watch the bougie attempt on an emergent intubation.

    what I didn’t know was that the department had very recently switched to the hyper-angulated glide-scope! so that was an interesting scenario as you might imagine.

    more recently I have learned, including at the last ResusX course, that you can still use a bougie with the hyper-angulated glide-scope, but its a good deal trickier for sure.

    again, thank you both! very cool blog.
    tom

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