Prehospital Advanced Airway Management with Neurologic Outcome and Survival in Patients with Out-Of-Hospital Cardiac Arrest
Out of Hospital Cardiac Arrest occurs in approximately 375-390K individuals yearly in the United States. Few interventions have ever been demonstrated to improve neurologically intact survival, and airway has always remained a priority in the initial resuscitation of the patients with cardiac arrest.
Despite this, advanced airway management in patients with cardiac arrest has never been shown to improve mortality. In fact, several studies have challenged the commonly held belief that advanced airway management in the pre-hospital setting improves mortality in trauma patients and pediatric patients.
In January JAMA published a prospective population based study completed in Japan looking at neurologically intact survival in patients who had pre-hospital advanced airway management (endotracheal intubation, or supraglottic airways) in a large cohort of patients.
1. Why is this topic important?
Pre-hospital advanced airway management has long been a part of many EMS protocols, despite the lack of evidence for improved neurologic survival. This study evaluates a large cohort of patients with pre-hospital cardiac arrest and attempts to evaluate the effect on mortality and neurologic function at one month using a modified rankin scale (mRS) in patients who have advanced airway management vs. bag-valve mask ventilation.
2. What does this study attempt to show?
The authors of the study believed that pre-hospital advanced airway management had no affect on neurologically intact survival. They defined their outcomes as return of spontaneous circulation (ROSC), one-month survival and neurologically intact survival at one month (mRS >/= 2). The authors chose a set of potential confounders a priori based on biological plausibility and a priori knowledge. Age, sex, cause of cardiac arrest, first documented rhythm, witnessed arrest, type of bystander CPR, use of public AED, epinephrine administration, and time interval from call to CPR by EMS and from receipt of call to hospital arrival were all chosen.
The authors recognized that a randomized controlled trial large enough to demonstrate clinical and statistical significance would be difficult due to the dismal outcome of cardiac arrest in general, and the large number of patients needed to show a meaningful difference. Instead they chose a population based study, completed prospectively acknowledging that potential confounders could have a significant impact on outcome.
3. What are the essential findings?
A total of 649,359 patients were ultimately included (658,829 eligible), 367,837 (56.7%) underwent bag valve mask ventilation, and 281,522 underwent advanced airway management (43.5%).
Of the patients who underwent advanced airway management a total of 41,972 (6.5%) received endotracheal intubation, and 239,550 received supraglottic airways (36.9%).
Table 1 shows the demographics of patients with out of hospital cardiac arrest.
Table 2 summarizes the survival outcomes, first unadjusted, adjusted for selected variables, and adjusted for all covariates.
An overview is provided for ease here:
Rates of ROSC:
Unadjusted:
-BVM 25, 904 (7%)
-Endotracheal Intubation 3,514 (8.4%)
-Supraglottic Airway 12,785 (5.3%).
OR (95% CI) vs. Bag-Valve Mask adjusted for pre-specified variables:
-Endotracheal Intubation 0.86 (0.82-0.89)
-Supraglottic Airway 0.64 (0.62-0.65)
One-month Survival:
Unadjusted:
-BVM 19,643 (5.3%)
-Endotracheal Intubation 1,757 (4.2%)
-Supraglottic Airway 9,176 (3.8%)
OR (95% CI) vs. Bag-Valve Mask adjusted for pre-specified variables:
- Endotracheal intubation 0.72 (0.70-0.73)
- Supraglottic airway 0.71 (0.69-0.72)
Neurologically Favorable Survival (mRS >/= 2)
Unadjusted:
- BVM 10,759 (2.9%)
- Endotracheal Intubation 432 (1%)
- Supraglottic Airway 2,724 (1.1%)
OR (95% CI) vs. Bag-Valve Mask adjusted for pre-specified variables:
- Endotracheal Intubation 0.41 (0.37-0.45)
- Supraglottic Airway 0.38 (0.36-0.40)
Plain Language summary-
The unadjusted model demonstrated significant negative associations between ANY advanced airway management and the 3 end-point measures (P < 0.001 for all outcomes).
In the adjusted model using selected variables and all variables advanced airway management were independent negative predictors of all 3 outcomes (p < .0001).
4. How is patient care impacted?
This is a tough pill to swallow. I bet many people believe that this does not make much physiologic sense, how can providing oxygen to an apneic patient result in worse outcomes? Is it the additional time needed to secure the airway (if this were true why is the signal still present in patients receiving a LMA?), is it that patients who have an esophageal intubation are likely to die of asphyxiation? Is hyperoxia and reperfusion injury contributing to a significant portion of morbidity in the post-anoxic injured brain?
Or is the study really not able to account for all the variables, and a potential unidentified confounder was driving the increased morbidity and mortality rather than the advanced airway itself?
Maybe it is time to reassess the importance of advanced-airway management in patients with OOHCA, and instead focus on chest compression early recognition of ventricular fibrillation with defibrillation, and finding secondary causes of arrest (no intubation, and no epi/bicarb/atropine/pacing unless indicated). If the patient obtains ROSC then all bets are off.
5. Is this an area of controversy?
There is really no point in stirring the pot with a mini-JC if there isn’t some type of controversy. Although some might argue that a true randomized clinical trial would be the only way to account for all differences in patients with OOHCA, I would argue that this is a large population based study. RCT’s are expensive, asses one intervention, apply only to a specific cohort of patients, and the OOHCA patients are a heterogenous group of patients. It is always difficult to account for every confounder, but in this study of almost six hundred thousand patients, there was a consistent signal of harm with pre-hospital intubation.
If this had completely gone against prior publications, it might raise a few more eyebrows, however, several studies have demonstrated that advanced airway management placed by pre-hospital providers does not improve and may worsen outcomes in patients with cardiac arrest.
6. Major Limitations of the study?
The study is non-randomized, and therefore most physicians argue that it cannot identify causation and only association. However, this is a large cohort study, the researchers identified a priori several possible confounders and attempted to adjust for these. The clinical end-point has been consistent in other smaller but more methodologically rigorous trials.
In addition they reran all the statistics favoring worse case scenarios in patients lost to follow-up and the signal of harm was still statistically and clinically significant.
Closing thoughts:
For me a 2% reduction in neurologically intact survival is important enough to have the discussion about changing pre-hospital management. Maybe one day we will learn that the drop in venous return, and subsequent hyperoxia from intubation was killing people. Whatever the truth may be the paper was worthy of a Mini-JC even if it might not change your practice tomorrow.
Till next time!
-Dave
Hasegawa et al. Association of Prehospital Advanced Airway Management With Neurologic Outcome and Survival in patients With Out-of-Hospital Cardiac Arrest. JAMA. 2013; 257-266.