Airway & Respiratory, Cardiac & Resuscitation

Effect of Prehospital Airway Management on Cardiac Arrest Outcomes

Historically, endotracheal intubation has been the defining skill of a paramedic. Unlike EDs with ample time, space, lighting and resources, EMS providers are often forced to act immediately and in a less than ideal environment.

Out-of-hospital cardiac arrest is the classic case of forced action without time to prepare, and cardiac arrest victims are the most frequent EMS intubations.

Recent conversations regarding cardiac arrest have focused on the importance of compression rate and depth, adequate recoil, peri-shock pauses, CPR density, “pit crew” modeling, mechanical compression devices and termination of resuscitation rules.

The American Heart Association even restructured the resuscitation alphabet to put “C” (Compressions) before “A” (Airway), all in the best interest of the patient.

While paying attention to compressions is of prime importance, the criticality of airway management still remains. This article will focus on prehospital airway management and reaffirm its impact on cardiac arrest outcomes.

By the Numbers

Let’s put things into perspective. There are approximately 300,000 cases of out-of-hospital cardiac arrest in the United States every year:

  • 80% will get an advanced prehospital airway;
  • 30% will be left at the scene after termination of resuscitation;
  • 33% will get return of spontaneous circulation (ROSC);
  • 25% will get admitted to the hospital;
  • 10% will survive to hospital discharge; and
  • 6% will be discharged neurologically intact.

The Choice

There are essentially three options to choose from to manage the patient’s airway during out of hospital cardiac arrest: Use of a bag-valve mask (BVM), a supraglottic airway (SGA) (e.g., Combitube, LMA, King, SALT) and endotracheal intubation (ETI). ETI is the most common intervention, but there’s growing support for SGAs as first-line airways, particularly to ensure that there are few interruptions in compressions during the early phases of resuscitation.

While some systems are very specific as to which method is used first, others allow the paramedic tasked with airway management to select the best device for the situation. Take a moment and reflect on your own practice, because the choices you make really do matter.

The Resuscitation Outcomes
Consortium Experience

The Resuscitations Outcomes Consortium (ROC), a multicity North American research network, has focused on improving out of hospital cardiac arrest and trauma care. The ROC Prehospital Resuscitation Using an Impedance Valve and Early vs. Delayed (PRIMED) study, prospectively enrolled about 10,000 subjects and randomized them to early vs. late rhythm analysis and real vs. sham impedance threshold device.1

While ROC PRIMED doesn’t directly address the role of prehospital airway management, the robust nature of the study allowed investigators to perform a secondary analysis of the data.

In this secondary analysis, 8,487 patients who underwent ETI were compared to 1,968 patients who had an SGA placed.2 Neurologically intact survival to hospital discharge was higher in those with ETI (4.7%) than those with an SGA (3.9%). After adjusting for many factors, such as age, initial rhythm and bystander CPR, the odds of survival were better for those with ETI (odds ratio of 1.4).

The odds for ROSC and 24-hour survival were also higher for patients with ETI and results persisted when patients with unsuccessful airway maneuvers were excluded.

A main limitation in interpreting these results lies in the source of the data. Agencies in the ROC undergo extensive and frequent training in out-of-hospital cardiac arrest care and may not be directly comparable to your system.
Also, these results are nested within a complex clinical trial and, although no difference was seen in the interventional arms of the trial, it’s difficult to know how those research interventions may have affected airway management. Regardless, in this group of patients, there’s a small but meaningful difference in outcomes based on how paramedics managed the patient’s airway.

The Japanese Experience

In 2013, a high-profile analysis of the All-Japan Utstein Registry was published in The Journal of the American Medical Association.3 Almost 650,000 patient records from a six-year period were analyzed and they concluded that BVM ventilation was associated with a 2.6 times greater chance of neurologically intact survival when compared to ETI or SGA placement.

The odds of achieving ROSC and one-month overall survival were also more common in patients managed with BVM and, similar to the ROC study, this was true even after adjusting for multiple patient factors.

In order to interpret their findings, though, the Japanese EMS system must be understood. Advanced life support, including ETI and SGA placement, is a relatively new skill. In fact, in this analysis, only 6% underwent ETI and 57% were managed with BVM alone; this sharply contrasts with common practices in the United States.

Additionally, approximately 18% of included cases suffered a traumatic arrest and these patients are expected to have dismal outcomes regardless of EMS interventions.

Finally, this analysis observed a low overall neurologically intact survival rate of 2.1%, which is approximately three times lower than in the U.S. Therefore, although specific airway management choices were associated with survival, there may have been other factors involved that altered the potential benefits of an airway procedure.

The Cardiac Arrest Registry
to Enhance Survival Experience

The Cardiac Arrest Registry to Enhance Survival (CARES) was created in 2004 as a collaboration between Emory University, the Centers for Disease Control and Prevention and the American Heart Association. Since that time, CARES has grown to include 40 participating communities in 25 states and has collected data on more than 73,000 cases of out-of-hospital cardiac arrest.

Similar to the Japanese registry, CARES allows insight into the broad practice of cardiac arrest resuscitation and presents an opportunity to explore the relationship between prehospital airway management and outcomes in the U.S.
An analysis of this database looked at almost 11,000 patients with out-of-hospital cardiac arrest in the calendar year 2011 and showed similar results to those seen in Japan.4 Patients who didn’t undergo advanced airway placement had better neurologic outcomes than those who received ETI or SGA (18.6% neurologically intact survival for BVM, 5.2% for SGA and 5.4% for ETI).

This was most true in patients found in initially shockable rhythms. In addition, similar to the ROC study, when the treating EMS providers decided to place an advanced airway, patients found in shockable rhythms had better neurologically intact survival with ETI compared to SGA.

There was no difference seen between ETI and SGA for cases of primary asystole or pulseless electrical activity.

Your Choice Matters

Balancing all of this information can be difficult because, unless you are part of the ROC, CARES or practice in Japan, these results may not be directly applicable to your personal practice. However, these three studies all show that prehospital airway management is significantly associated with neurologic outcomes. Your choice matters.

Association Doesn’t Equal Causation

All of this evidence comes from a retrospective look back at how patients were treated, without knowing the details of the resuscitations or the thought process behind each individual decision by the treating EMS providers.

Most likely, our “one-shock wonders” with immediate return to consciousness after initial defibrillation are all included in the groups that had no advanced airway, because there was no need for an airway; this could bias the “no airway” group toward better outcomes.

However, the no airway group is also the default for all patients where attempts at airway placement failed, and it’s plausible that these patients could have the worst outcomes because of inherent interruptions in chest compressions that occur with airway maneuvers.

Honestly, there are unmeasured and unmeasurable factors that influence both the airway decision and the patient’s outcome no matter how hard you try to control for them, which is why a causal relationship is difficult to determine.
A common mistake in interpreting these results is confusing association and causation. Crudely, association means that two things are related in some way or are often found together, whereas causation implies a definite cause-and-effect relationship.

Consider this example: Use of lights and sirens is associated with ambulance crashes. Lights and sirens don’t cause ambulance crashes. So, the strongest conclusion we can make from these studies is that prehospital airway management and neurologically intact survival are linked. The challenging next step is determining why?

Trust. Professionalism. Perfection.

There’s a divine contract between you and your patient when you manage their airway. We all know the Rifleman’s Creed: “This is my rifle. There are many like it, but this one is mine …”

We must treat our laryngoscope and everything else in our airway bag in the same way. We must move beyond the technical skill of airway management and toward an understanding of what happens during and after we manage an airway. After all, pulling a trigger may itself be quick, easy and harmless, but the potential repercussions can be devastating.

Positive Pressure Ventilation
is the Devil …

The inevitable and immediate physiologic change that occurs after ETI or SGA placement is the conversion from normal negative pressure ventilation to abnormal positive pressure ventilation. In the apneic patient, ventilation by a BVM has the same effect on physiology.

In a normal, healthy person the diaphragm drops during inhalation, the thorax expands and air is drawn into the lungs due to a decrease in intrathoracic pressure. Often overlooked is the fact that the drop in intrathoracic pressure during normal respiration also augments venous return to the heart, increasing preload. This facilitates adequate perfusion of the brain.

The opposite occurs with positive pressure ventilation. Intrathoracic pressure abnormally rises when we ventilate a patient through an advanced airway or with a BVM. The consequences are significant: venous return falls, preload decreases and cardiac output declines. Thus, every positive pressure breath limits coronary and cerebral perfusion. In addition, even optimized chest compressions during cardiopulmonary resuscitation fall far short of matching normal cardiac output, which further decreases blood flow to the brain.

… and Hyperventilation is His Bride

We all tend to hyperventilate our patients. Physicians, nurses, respiratory therapists, paramedics and EMTs—no one is immune. Often we do it subconsciously. Sometimes we do it in an effort to make up for hypoxia due to prolonged apnea time. (This logic is wrong, by the way, because increasing the respiratory rate does not improve oxygenation.) No matter what the reason, hyperventilation is always wrong in cardiac arrest management.

Hyperventilation causes hypocarbia, and this decrease in the carbon dioxide in the blood leads to vasoconstriction of the cerebral vessels. We use this to our advantage in the severe traumatic brain injury patient who is herniating. However, in patients suffering from cardiac arrest, this phenomenon is adding insult to injury because cerebral perfusion is already compromised by use of positive pressure ventilation.

Do No Harm (and Do “Know” Harm)

Treatment priorities are established as soon as the first rescuer reaches a patient in cardiac arrest and each decision made should be done to maximize the chance of neurologically intact survival.

We all agree that high-quality, uninterrupted chest compressions are absolutely essential, and rapid treatment of shockable rhythms is arguably the highest of all priorities. The three studies highlighted above lend support to deemphasizing airway management, but, eventually, the airway is almost always actively managed.

Consider these suggestions:

  • Resurrect the art of BVM ventilation. This skill is harder than we remember. Practice today, tomorrow and at least as often as you practice other airway skills. If you have enough personnel, allocate two providers for rescue breathing and use the two-handed thumbs down technique to hold the mask. Also, using bilateral nasopharyngeal airways and an oropharyngeal airway truly helps.
  • Use feedback devices whenever possible to avoid hyperventilation. Capnography is the best method, because airway placement is confirmed with each breath and the respiratory rate can be visualized. Metronomes, flashing timer lights and tactile feedback resuscitation bags are also reasonable adjuncts.
  • Finally, pay attention to your crew’s approach to airway management. Multiple providers making multiple attempts at ETI isn’t acceptable if high-quality continuous chest compressions are compromised. Even a single successful attempt may harm the patient in the long run if compressions are interrupted or hypoxia time is prolonged. Some airways are truly difficult, but the key is to always optimize your environment and make it count.

The Bottom Line

Although the best methods for resuscitation may differ from one EMS system to another, EMS airway management will always be a critical component of cardiac arrest management. We may not know exactly why, but it’s clear that your choices have downstream impacts on survival and quality of life. ETI may be beneficial in some patients, whereas a BVM may suffice in others.
No matter which ventilation method is used, you must monitor the effect and guide your team to provide effective ventilations, just as you guide them for effective compressions.

Why do all this? Because, selfishly, I may be one of the lucky ones who survives my first death; and I want my brain fully functional in-between.

References

1. Stiell IG, Nichol G, Leroux BG, et al. Early versus later rhythm analysis in patients with out-of-hospital cardiac arrest. N Engl J Med. 2011;365(9):787–797.

2. Wang HE, Szydlo D, Stouffer JA, et al. Endotracheal intubation versus supraglottic airway insertion in out-of-hospital cardiac arrest. Resuscitation. 2012;83(9):1061–1066.

3. Hasegawa K, Hiraide A, Chang Y, 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):257–266.

4. McMullan J, Gerecht R, Bonomo J, et al. Airway management and out-of-hospital cardiac arrest outcome in the CARES registry. Resuscitation. 2014; 85(5):617–622.