Feb 212013
Intubation for Out-of-Hospital Cardiac Arrest May Harm, Not Help

by Blair Westerly, MD

Out of hospital cardiac arrest is a major public-health problem, and despite advances in care, survival is still low. Improved survival has been associated with early CPR, rapid defibrillation, and integrated post cardiac arrest care, but pre-hospital "advanced airway management" (i.e., intubation by EMTs) has never been shown to be beneficial. On the contrary, small observational studies (n~2,500) have associated intubation in the field with worsened survival to hospital discharge. Nevertheless, it is common for advanced airway management to be attempted as a component of advanced life-support. A new study in JAMA using a huge dataset of out-of-hospital cardiac arrests in Japan lends further strength to this concerning hypothesis: does intubation after out-of-hospital cardiac arrest harm people?

What They Did

Hasegawa et al performed a prospective, nationwide, population based study using Japan’s national registry of nearly 650,000 patients with out-of-hospital cardiac arrest over a 5-year period to compare neurological outcomes of those receiving advanced airway management versus those who underwent bag mask ventilation.

Here are a few important things to note about the Japanese EMS system:

  1. All CPR was performed according to Japanese CPR guidelines, which are based on guidelines from AHA and International Liaison Committee on Resuscitation.
  2. EMS providers allowed to perform endotracheal intubation had undergone an additional 62 hours of training sessions and performed 30 supervised successful intubations in operating rooms (that’s 25 more than US and 5 more than UK, in case you weren’t aware)
  3. Up to two attempts at an advanced airway management (ET tube or supraglottic device) were allowed after initial rhythm check, using defibrillation when appropriate, chest compressions, and bag mask ventilation were performed per guidelines.
  4. End-tidal CO2 or esophageal detection device were used to confirm successful device placement.

Primary endpoint was favorable neurological outcome as defined by the Glasgow Pittsburgh Cerebral performance category 1 or 2. Categories 3, 4, or 5 were regarded as an unfavorable neurological outcome. Secondary end-points were survival and return of spontaneous circulation before hospital arrival.

Of note, a priori, the authors selected several variables that were likely to influence outcomes as confounders, based on previous data and physiologic probability.

Because airway management was not randomly assigned, propensity scoring was used to protect against potential selection bias and confounding. A case-control analysis was then used to compare those who underwent advanced airway management with those who underwent bag mask ventilation.

What They Found
  • Bag mask ventilation was used more commonly than advanced airway: 56.7% vs 43.4% (6.5% endotracheal intubation and 36.9% supraglottic airways)
  • 6.5% had return of spontaneous circulation, 4.7% were alive at one month, and 2.2% had a neurologically favorable survival.
  • 2.9% in the bag mask ventilation group had a favorable neurological outcome versus 1.1% in the supraglottic airway and 1.0% in the endotracheal intubation groups; this was a significant difference.
  • Advanced airway management was negatively associated with outcomes for all three endpoint measures in the unadjusted model and the adjusted model using the a priori variables
  • Even when assuming the worst for those lost to follow-up receiving bag mask ventilation and assuming the best for those lost follow-up receiving advanced airway, advanced airway placement was still associated with poor neurological outcome.
  • Poor neurological outcome persisted again in the advanced airway group when adjusting for achievement of return of spontaneous circulation in addition to be selected variables
  • In the propensity matched analysis the unadjusted model showed negative association with advanced airway and all three endpoint measures.
  • In multivariable models using selected or all variables, again significant negative associations were detected between any type of advanced airway and the three outcome measures.
What It Means

This large, observational, population-based study shows a clear negative association between advanced airway management and neurologically favorable survival after cardiac arrest that persisted after many different analytic assumptions. Remember, the negative association in an observational study cannot prove causality and might be related to confounders that were not measured (patient factors, rescuer factors, situational factors, etc), though I give the authors credit for the a priori variables identified in a methodologically compelling design.

The American Heart Association (who makes the ACLS protocols) takes a neutral-to-negative stance toward advanced airway placement for out-of-hospital cardiac arrest in its 2005 ACLS guidelines: not discouraging the practice, but emphasizing:

Rescuers must be aware of the risks and benefits of insertion of an advanced airway during a resuscitation attempt ... Advanced airway interventions are technically complicated, failure can occur, and maintenance of skills through frequent experience or practice is essential.It is important to remember that there is no evidence that advanced airway measures improve survival rates in the setting of prehospital cardiac arrest."

Ultimately, all providers involved need to question our usual modi operandi and ask if what we do is really what is best for the patient.  The enormous size of the study will make it difficult to replicate in a randomized trial, but these results beg for additional exploration into the underlying mechanisms of the negative association observed (perhaps lack of adequate chest compressions, hyperventilation, hyperoxia/hypoxia or increased intrathoracic pressure) and we hope RCTs can help clarify this important component of resuscitation so pre-hospital (and hospital) care can continue to improve.

Clinical Takeaway: Intubation's inclusion as an essential component of care for out-of-hospital cardiac arrest was debatable before this study; now, expect many physicians to consider it thoroughly "optional." Watch for possible revisions of the ACLS guidelines by the American Heart Association and from other specialty societies.

Hasegawa K et al. Association of prehospital advanced airway management with neurologic outcome and survival in patients with out-of-hospital cardiac arrest. JAMA 2013;309(3):257-26.

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Intubation in pre-hospital cardiac arrest strongly associated with worse outcomes