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)
- 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.
- 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.
- 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.
- Toda, J., Toda, A. A., & Arakawa, J. Learning curve for paramedic endotracheal intubation and complications. Int J Emerg Med, 6(1), 38.
- 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.
- 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.
- 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.
- Kern, K. B. Optimal treatment of patients surviving out-of-hospital cardiac arrest. JACC Cardiovasc Interv, 5(6), 597-605.
- Thompson, J. (2003). Ethical challenges of informed consent in prehospital research. CJEM, 5(2), 108-114.