Should Paramedics Intubate Out-of-Hospital Cardiac Arrest?

Airway management of out-of-hospital cardiac arrest is a controversial topic.  Most patients transported for OHCA have receive prehospital airway management.  However, attempts at establishing an airway can interrupt compressions, over-ventilation can decrease cerebral perfusion, and delays in airway acquisition impact transport to definitive care.

This study retrospectively evaluates the CARES surveillance group, a multi-site registry from North America, comparing neurologically intact survival after prehospital endotracheal intubation, supraglottic airway, or no advanced airway.  In the unadjusted results, survival rates were 5.4% for intubated patients, 5.2% for supraglottic airway, and 18.6% for no advanced airway.  After statistical adjustments and propensity scores, the authors report the ultimate winner is not attempting an advanced airway – and then endotracheal intubation is superior to supraglottic airway.

But, really, this study tells us nothing.  Even though the authors attempt several methods of statistical adjustment, the likely presence of massive unmeasured confounders invalidates these observations.  There is an entire host of patient-level and situational factors that impact the type of airway attempted, the number of airway attempts, and the aggressiveness of care provided both pre-hospital and in-hospital.  The profound differences in unadjusted outcomes, between those not receiving an advanced airway and those requiring one, paints the most obvious picture of the likely underlying differences in unfavorable physiology at work.

This is hardly the first observational report regarding the impact of prehospital airway management.  And, frankly, we’ve seen enough – this type of retrospective cohort does not hold the answer, unless the registry was specifically designed to answer such questions.  To the authors credit, they do not overstate the level of evidence provided – but an unsophisticated reader might draw the wrong conclusions.

“Airway management and out-of-hospital cardiac arrest outcome in the CARES registry”
http://www.ncbi.nlm.nih.gov/pubmed/24561079

6 thoughts on “Should Paramedics Intubate Out-of-Hospital Cardiac Arrest?”

  1. I think the real problem in this type of cardiac arrest research is just how poorly most of the US handles OHCA. Until CPR quality (depth, rate, fraction) can be reported alongside this data I don't even want to see it. All modern cardiac monitors record data capable of providing these quality metrics, we just don't routinely see it in the literature (excluding the work by Bobrow et al).

    Consider the case of service X with poor CPR quality (compression fraction <80% and they transport with CPR in progress for instance), who runs 1000 cardiac arrests in a year and a baseline survival to discharge of 6%. Let's say they do away with ETI or SGAs and go BVM only…if they have a statistically significant rise in survival to 7.5%: how can I even begin to use that information knowing that CPR quality improvements alone would easily double their numbers?

    The variability in delivery and survival makes these retrospective studies even less useful to system designers and protocol writers. If I know my system gets >30% Utstein survival with high quality CPR and paramedic's choice in airways, am I really going to take the word of a system(s) of unknown or low quality resuscitation in my airway choice?

  2. I think you've identified, essentially, why all this data is useless – because, as you say, there is so much variability across a multi-center trial, and you don't know anything about the individual protocols in place, the quality of the interventions, etc.

    There's no good reason to publish this data; it does not, and cannot, support any actionable conclusion.

  3. I think these statistics are skewed by patients who are successfully converted early in to resuscitation who are both most likely to survive and most likely to regain consciousness — both major factors in why advanced airways might not have been obtained.

  4. Absolutely – and that's why all the statistical adjustments in the world aren't useful in an unbalanced, retrospective cohort such as this.

  5. Yes Ryan agree.

    I think it is time for a moratorium on retrospective studies looking at intubation after out of hospital cardiac arrest. THE HYPOTHESIS HAS ALREADY BEEN RAISED! Please stop the nonsence. If you want to go further with this then please do a proper RCT.

    The only RCT that I am aware of was the pediatric study by Dr Marianne Gauche in Los Angeles. I don't believe an adult study has been done. As far as airway is concerned, adults are quite different from children so I am not sure we could really extrapolate. In addition, I think this was an even/odd day pseudorandomization. So not the greatest answer to the question anyway.

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