Another Pre-hospital Airway Registry Publication

I had another paper brought to my attention tonight by a fellow #FOAMed tweep:  Airway management and out of hospital cardiac arrest outcome in the CARES registry (ePub ahead of print) in Resuscitation (1)

I’ve flicked through the paper reasonably quickly, so there are bound to be things that I have missed.  If you find any, please let me know!

The CARES Registry is a large, voluntary registry for EMS agencies in the US to collate data on cardiac arrest, and seems to be similar in aims as out VACAR registry.  It collates data from a large number of state and municipal services in order to improve cardiac arrest survival.  This paper looks at the difference in outcomes for people in cardiac arrest who receive either no advanced airway, a supra-glottic airway (SGA) or endotracheal intubation (ETI)

So what does this paper tell us?  Well, in some ways, not much.  This is not a criticism of the authors or the paper though.  Rather it is recognition that it is extremely difficult to carry out research in the pre-hospital field, especially in settings with multiple confounders such as cardiac arrest.

The main results in this paper are ROSC, survival to hospital, survival to discharge and survival to discharge with good neurological function.  In my opinion the last one is the only really important, patient orientated outcome that matters.  There is a lot of statistical voodoo that I won’t pretend to understand particularly well.  However, Table 3 is at least easy enough for me to understand:  Patients who received no advanced airway had a significantly higher survival to hospital, survival to discharge and good neurological outcome.

The outcomes between SGA and ETI are less pronounced, however it appears that patients who are intubated have slightly better outcomes than those who receive a SGA.
When we look at the characteristics of the patients who get no advanced airway we see that they are significantly more likely to be young, have a cardiac arrest witnessed by EMS or other health professionals.  To me, therefore, it is not surprising that these patients do better than those who are found down, or drop at home.  If your patient goes toes up in front of you and you immediately apply electricity and CPR, it would seem obvious that these patients should do relatively well.

There are many other confounders of course.  For Australasian readers it is hard to generalise results from the US to our practice.  It is worth noting that there is an 18.2% failure rate of intubation, which is certainly significantly higher than Victorian MICA paramedics would expect to have.  The rate of failed intubation may actually be higher: SGA insertion is often part of a failed airway drill, and thus insertion of SGA may in fact represent a surrogate for failed intubation.  Also, as this a self reported registry it would not be unreasonable to assume that failure may be slightly higher than reported.

We also do not know who is doing the intubating: it appears that experience is a very important predictor of success in airway management, and not just experience on mannequins, but in actual people (2, 3, 4, 5, 6)  I don’t think it is unreasonable to expect that prolonged attempts or pausing CPR to attempt intubation would result in worse outcomes and this may be more common in less experience operators.  We do not know the quality of post airway insertion ventilation, nor any other measures such as BP management in the field (which may be important(7)), whether PCI was performed (8) and so on.

In short, despite some impressive (well, impressive to me…) statistical manipulation to account for various confounders, there is simply too much we don’t know, and perhaps too much that we can’t know when dealing with pre-hospital cardiac arrest.
The authors of this paper expressly acknowledge and discuss this important issue: research in the pre-hospital field is difficult.  It is difficult due to ethical issues (9), and it is difficult due to practical issues.  Anyone who can carry out high quality research, even if it is a registry such as this, should therefore be applauded.

Ultimately, does this paper give us anything to change the way we (the Australasian ‘we’) manage the airway in cardiac arrest?  I don’t believe so.  This is not bad paper, but I think that for me at least, it reinforces what I already think about advanced airway management in general and specifically with regard to cardiac arrest: Advanced airway management done well is probably good; advanced airway management done poorly is definitely bad; and doing the basics well is the most important thing.

I would love it if anyone with a better head for statistics felt like reading this paper and letting me know what they come up with.


Hey look, I referenced a blog post! (don’t get used to it)

  1. McMullan, J., Gerecht, R., Bonomo, J., Robb, R., McNally, B., Donnelly, J., et al. Airway management and out-of-hospital cardiac arrest outcome in the CARES registry. Resuscitation.
  2. Fullerton, J. N., Roberts, K. J., & Wyse, M. (2009). Can experienced paramedics perform tracheal intubation at cardiac arrests? Five years experience of a regional air ambulance service in the UK. Resuscitation, 80(12), 1342-1345.
  3. Garza, A. G., Gratton, M. C., Coontz, D., Noble, E., & Ma, O. J. (2003). Effect of paramedic experience on orotracheal intubation success rates. J Emerg Med, 25(3), 251-256.
  4. Toda, J., Toda, A. A., & Arakawa, J. Learning curve for paramedic endotracheal intubation and complications. Int J Emerg Med, 6(1), 38.
  5. Wang, H. E., Seitz, S. R., Hostler, D., & Yealy, D. M. (2005). Defining the learning curve for paramedic student endotracheal intubation. Prehosp Emerg Care, 9(2), 156-162.
  6. Warner, K. J., Carlbom, D., Cooke, C. R., Bulger, E. M., Copass, M. K., & Sharar, S. R. Paramedic training for proficient prehospital endotracheal intubation. Prehosp Emerg Care, 14(1), 103-108.
  7. Bray, J. E., Bernard, S., Cantwell, K., Stephenson, M., & Smith, K. The association between systolic blood pressure on arrival at hospital and outcome in adults surviving from out-of-hospital cardiac arrests of presumed cardiac aetiology. Resuscitation, 85(4), 509-515.
  8. Kern, K. B. Optimal treatment of patients surviving out-of-hospital cardiac arrest. JACC Cardiovasc Interv, 5(6), 597-605.
  9. Thompson, J. (2003). Ethical challenges of informed consent in prehospital research. CJEM, 5(2), 108-114.
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2 Responses to Another Pre-hospital Airway Registry Publication

  1. James Oz says:

    First of all I’d like to say I quite agree with your airway done well = good, airway done badly = very bad. Obviously I have very little in the way of practical experience with this, but speaking from my understanding of the literature, that seems true and there are obvious issues with generalizing American paramedic airway studies of any kind because of the vast differences between our systems. The apparent fondness that Wang fella and others have for giving paramedics very little education, a tube, a laryngoscope, 2mg of midaz and one opportunity per year to actually use them, then conclude that paramedics can’t intubate, doesn’t help.
    The point that I was trying, somewhat in vein, to make on twitter was that I think its important to recognize, analyse and discuss new data like this paper with a view to constantly look for ways in which we could be doing a better job of patient care. Just because MICA do this well, doesn’t mean it couldn’t be done better. I agree that this paper isn’t practice changing, but it adds to the questions I have and I’d like to see some more data of better quality before we put some of these issues to bed.
    The SGA seems to be taking on a bigger and bigger role. The concept of the rapid sequence airway is a good example of one of the ways in which the LMA in particular appears to have been elevated significantly beyond a mere rescue device. Early discussions with several paramedics about the iGel suggest to me that this will extend to the ALS level and that the iGel may take on a role in our algorithms more akin to the OPA than the LMA (at least as ALS have viewed it traditionally).
    With that in mind, I think papers like this should at least raise an eyebrow or two in regards to SGAs.
    A couple of points further to previous discussion:
    – The worse outcomes in SGA Vs ETI was consistent with ROC studies which include some pretty sharp US services as well as Canadian EMS. I don’t think this can be blamed entirely on rubbish US EMS. Additionally they adjusted for regional variance. Now I have no idea what this really means or how effective it is, but it should, to some degree address the bad apple effect and smooth things out a bit.
    -The point about airway training, competency and exposure doesn’t really hold up in relation to the SGA stuff to my mind. The supposedly idiot proof SGA should be the easier, faster (less time off chest) all round better modality if training/competency were the only issues. This doesn’t prove anything of course but I don’t think its right to apply the same rebuttal to this study as to the US EMS airway studies looking at the failure of ETI.
    Maybe its because failed tubes progress to SGA and they don’t do well because they attempted ETI 600 times or something..or maybes its some other weird issue. Sure. This paper doesn’t answer anything, it just nags at you; is there something wrong with SGA?
    EDIT: Soooo..I just noticed that LMAs actually constitute almost none of the SGAs so that sorta ruins that entire line of thought in regards to Vic. Still….I.. er… hmmm….ooopps.
    In relation to advanced airway vs nada, I agree that there is little that can be drawn from this study for Aus/NZ. Now that assumes that you’re ALL better than these American paramedics and I can tell you that you aren’t. Not all of you. But I assume you know this. Some of the most complete fuck ups some of us have been involved with were ETI related. Real shockers. Now I assume you would say that this is an educational issue, not an issue with the intervention itself and I’d agree completely. In this sense though I think that this paper supports the notion that airway done badly might lead to pretty spectacularly bad outcomes which should make us even more carefully evaluate who does this shit and how we prepare them. Much like you said, I think this adds to (not confirms) what we already think we know. My understanding is that the clinical department is working on this issue in the form of some sort of minimum exposure training or something. I’d be interested to hear more about that.

    • I have absolutely no argument that we always need to be looking to do things better. This is one of the main reason I am so keen on FOAMed and why I write this blog. I want to be better at what I do, and FOAMed is the best way I have found of facilitating that. I want to punch something every time I hear “world’s best”. Not because it’s a bad thing to be proud of what we do, but because when we do that, we rest on out laurels, we ignore what everyone else is doing well (or better than us) and we cease to provide the best we can for our patients.

      However with regards to this paper, I genuinely don’t think we can take a great deal away from it with respect to our current practice. The fact that patients who arrest in front of a paramedic both A) don’t get intubated and B) do well doesn’t really tell us anything earth-shattering. The apparent inferiority of SGA is interesting, but given that we don’t typically use SGA in cardiac arrest I don’t think that it affects us much. We know that, generally speaking, MICA paramedics are very good at the procedure of intubating when compared to the broader US EMS population (1). There are undoubtedly many services in the US who are extremely good at airway management. This is not the broader population that we are seeing in the literature. So if we are able to safely and effectively place an ETT during arrest, and ETI appears to be superior to SGA in arrest anyway, then I can’t see how we could justify changing our practice.

      I guess the question then, is should we place an advanced airway at all. Again, given our success with intubation and the paucity of relevant evidence currently, I’m not sure that this would be appropriate. Perhaps in the setting of an RCT?

      Cardiac arrest research is very difficult due to the vast number of confounders that abound. One advantage that we have is that knowing we are able to place an ETT appropriately and safely, we can take the airway confounder out of the equation. We can then focus on everything else (ventilation, drugs, mechanical ventilation, intra-arrest cooling etc)

      This paper is not a bad piece of research, but it is what it is: a registry that takes a snapshot of what is happening, in the US at one point of time. It is not the sort of paper that changes practice, it is the sort of research that suggests avenues of research.

      1. Wang, H. E., Mann, N. C., Mears, G., Jacobson, K., & Yealy, D. M. Out-of-hospital airway management in the United States. Resuscitation, 82(4), 378-385.

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