JC: Macintosh vs. McGrath laryngoscopy in pre-hospital care.

There has been an ongoing debate about the use of video laryngoscopy (VL) in emergency and critical care​1–4​. Proponents speak of the better visibility and ability to teach using video systems whereas those preferring a direct laryngoscopic (DL) approach speak to a more rapid, tried and tested technique. A few studies exist which in general have favoured DL owing to the increased time, equipment and process steps required for VL, but in truth we don’t really know. The field is also complicated by the wide range of different equipment, patients and settings that previous trials have described.

In my personal practice I use a DL approach using a Macintosh blade, but I have access to a McGrath videolaryngoscope if I need it. So far (touch wood) I’ve not needed a VL as a rescue device very much, as DL in our unit seems to work very well.

This month we have a paper in Critical Care Medicine that looks at VL vs. DL in a population similar to my ED population and thus it’s a paper that might help inform the debate​5​. The abstract is below, but as we always say, please read the full paper before making up your mind on the validity of the outcomes.

What kind of paper is this?

It’s a randomised controlled trial which is an appropriate and high quality method to compare two interventions, in this case VL vs. DL. This is described as an equivalence study.

Tell be about the equivalence concept?

The authors talk of this study as an equivalence study with the aim of detecting a difference of up to 6.5%. That’s an equivalence of achieving intubation at any point and not at first pass which is arguably a better concept in these sort of trials. Moreover, that’s quite a big difference and more than we would accept in clinical practice (Ed – would you consider a 6.5% difference equivalent?). They originally intended to recruit over 900 patients to be sure of this, but following an interim analysis at the half way point the trial was stopped (Ed – though this is not described why though). Personally I think that was a mistake based on the original power calculation accepting a very wide degree of what is equivalence. It also means that many of the sub group analyses rely on quite small numbers.

Tell me about the patients.

This study was conducted in the prehospital setting in Austria. Their HEMS service randomised patients who required tracheal intubation to a first attempt with either a McGrath videolaryngoscope (VL) or a standard Macintosh laryngoscope (DL). If the first attempt failed then the clinician could choose whether to swap to the other device or continue with the same method.

The patients were aged >17 and as you would expect in a HEMS service pretty sick. Half of them were in cardiac arrest, the rest a broad mix of medical and surgical patients. Notably the number of trauma patients was roughly a third of those enrolled.

Patients in cardiac arrest were intubated without drugs, all the others got an RSI package. A variety of drugs were used, but the vast majority included a paralytic agent (sux or roc).

The groups look fairly even at baseline, but the high proportion of patients in cardiac arrest probably accounts for the skewed aged distribtion with an overall average of 65.

What did they find?

They managed to randomise and analyse 514 patients, which makes this a moderately sized study. Overall the authors state that there is no difference between the techniques, but I’m not so sure.

For success at first pass the rates were 83% for DL and 79% for VL. To be precise it was a 3.97% difference with wide confidence intervals. Certainly wider than the 6.5% stated in their power calculation. It’s also a fairly low first pass success rate. I ran an analysis of just the first pass success rates using a Fisher exact test​6​ and the result is not significant (p=0.26) so we cannot draw a conclusion here, apart from the fact that the trial is underpowered to show quite a significant difference. I also ran the stats for a power calculation on detecting a 4 percent difference as seen here and such a trial would require around 1500 patients in each group.

The study describes up to 4 further attempts, and these got the success rates up to 95.3 (DL) vs 93.8 (VL) at second attempt and then slightly better with third and fourth until alternative airways were created in the remainder. By the final attempt there was only a 0.4% difference and so the authors claim equivalence. However, there was considerable swapping around of laryngoscopes if the first attempt failed. A subgroup analysis, albeit with small numbers, suggests that changing laryngoscopes increases the chance of success.

The authors suggest that the McGrath gives a better view, but that is is more difficult to use and is more prone to technical difficulties. A whole bunch of sub analyses have been performed that suggest differences and possible explanations for this, but they are mostly small numbers of patients analysed and not corrected for multiple analyses.

So does this answer the question about whether VL is better than DL?

Not really in my opinion. This study tells us that if you have both available then the chances of success are high. First pass attempts might be better with DL, but we don’t really know.

It’s also worth noting that this study used the McGrath with a standard blade such that it can be used as a DL, and so there is an argument here that the differences are really rather minimal. There is a hyperangulated X blade available for the McGrath which requires a different technique to achieve intubation. If you can use the McGrath as a DL, then is this study really that much of a comparison of difference in technique? Arguably the VL first approach should lead to a greater first pass success owing to the ability of the operator to move from a DL to a VL technique seamlessly, but that does not seem to have been the case here.

What’s the bottom line?

Well done to the authors for conducting a prehospital RCT on a time critical intervention. The effort and team work to achieve this must have been remarkable.

In terms of the results, the bottom line appears to be that both techniques work in the majority of cases. Having access and training on both devices achieves a very high success rate following up to 4 attempts at laryngoscopy.

vb

S

@EMManchester

References

  1. 1.
    Carley S. Did video kill the laryngoscope star? St Emlyn’s. http://www.stemlynsblog.org/video-laryngoscopy-an-rct-in-trauma-st-emlyns/. Published 2013. Accessed 2019.
  2. 2.
    Carley S. If the video laryngoscope was stroke thrombolysis. St Emlyn’s. http://www.stemlynsblog.org/of-course-if-the-video-laryngoscope-was-stroke-thrombolysis/. Published 2013. Accessed 2019.
  3. 3.
    Lewis SR, Butler AR, Parker J, Cook TM, Smith AF. Videolaryngoscopy versus direct laryngoscopy for adult patients requiring tracheal intubation. Cochrane Database of Systematic Reviews. November 2016. doi:10.1002/14651858.cd011136.pub2
  4. 4.
    Janz DR, Semler MW, Lentz RJ, et al. Randomized Trial of Video Laryngoscopy for Endotracheal Intubation of Critically Ill Adults*. Critical Care Medicine. November 2016:1980-1987. doi:10.1097/ccm.0000000000001841
  5. 5.
    Kreutziger J, Hornung S, Harrer C, et al. Comparing the McGrath Mac Video Laryngoscope and Direct Laryngoscopy for Prehospital Emergency Intubation in Air Rescue Patients. Critical Care Medicine. August 2019:1. doi:10.1097/ccm.0000000000003918
  6. 6.
    stat pages. Fisher Exact test. statpages. https://statpages.info/ctab2x2.html. Published 2019. Accessed 2019.

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Posted by Simon Carley

Professor Simon Carley MB ChB, PGDip, DipIMC (RCS Ed), FRCS (Ed)(1998), FHEA, FAcadMed, FRCEM, MPhil, MD, PhD is Creator, Webmaster, owner and Editor in Chief of the St Emlyn’s blog and podcast. He is Professor of Emergency Medicine at Manchester Metropolitan University and a Consultant in adult and paediatric Emergency Medicine at Manchester Foundation Trust. He is co-founder of BestBets, St.Emlyns and the MSc in emergency medicine at Manchester Metropolitan University. He is an Education Associate with the General Medical Council and is an Associate Editor for the Emergency Medicine Journal. His research interests include diagnostics, MedEd, Major incidents & Evidence based Emergency Medicine. He is verified on twitter as @EMManchester

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