How EMTs and paramedics manage the airway during out of hospital cardiac arrest (OHCA) should matter to all emergency physicians, even if you are not an EMS medical director. More and more evidence suggests that what happens in the field has a major impact on our patient's outcome, and clearly it affects what we do in the ED.
One of the latest controversies in EMS is whether endotracheal intubation (ETI) is superior to extraglottic airway (EGA) placement during OHCA. ETI has been the clear gold standard, but a body of evidence growing over the past 10 years shows poor success rates for paramedic intubation and more evidence that any interruption in chest compressions negatively affects outcome. Major developments in EGA technology and a real push to move this technology from the OR to the field, from a secondary “rescue” role to a primary role, are also driving reconsideration of EGA. The vast majority of OHCA cases in my EMS, for example, are managed with an EGA without any attempt at intubation.
Studies now suggest that ETI may be superior to EGA placement for OHCA, as I wrote in EMN last year. (EMN 2013;35:1; http://bit.ly/1hX5wxl.) The major attacks on EGAs have come from large databases where outcomes have been generally better for patients managed only with bag-mask ventilation (BMV) and for patients managed with ETI compared with an EGD. It is very exciting to have outcome-based studies in EMS, but two major barriers have prevented adopting these findings: many of the studies were done in Japan where the EMS practice is unique and findings cannot necessarily be extrapolated to other countries, and the studies have not been able to stratify patients based on prognosis.
The reason, in other words, is that a patient is not intubated or does not receive an EGD in most systems because he has been converted with an initial shock. Of course, that patient will do better than one who did not convert and required a long resuscitation, including intubation or EGA placement. The study is inherently flawed if it cannot distinguish into which group the patients fall.
The latest important research to address this hot topic comes from Jason McMullan, MD, at the University of Cincinnati and colleagues from Emory and the University of Alabama. Their paper, “Airway Management and Out-of-Hospital Cardiac Arrest Outcome in the CARES Registry,” was presented at this year's meeting of the National Association of EMS Physicians, and is currently in press at Resuscitation. CARES, the Cardiac Arrest Registry to Enhance Survival, includes more than 400 EMS agencies covering a population of 65 million people. This study reports on more than 10,000 prehospital cardiac arrests; about half were intubated, a third were managed with an EGD, and the remainder had neither, most likely BMV but possibly no PPV at all. Neurologically intact survival to hospital discharge was slightly higher in the ETI group than the SGA group (OR 1.41), but more importantly, the group that had no advanced airway had a much higher rate of neurologically intact survival with an OR for favorable outcome of 4.2.
This provocative research might erroneously lead some emergency and EMS physicians to recommend the use of ETI over an EGA or no device at all for prehospital management of cardiac arrest. These conclusions may well turn out to be true, but this paper cannot provide the guidance we seek. The major shortcomings, acknowledged by the authors, are that the total number of attempts and unsuccessful insertions were not reported, and we do not know enough about the group that did not get an advanced airway. Most importantly, we do know if they were successfully shocked and converted early, which is quite likely, because we know from the registry that they more often presented in a shockable rhythm and after a witnessed cardiac arrest.
If just one-third of the EGDs were placed after unsuccessful ETI attempts rather than primarily, then the results would be dramatically different by an intention-to-treat analysis. If we were able to compare patients who had similar durations of positive pressure ventilation by bag-mask with positive pressure only by intubation or only by extraglottic device, then we would have a more meaningful comparison.
For now, what we know with some certainty is that early defibrillation is good; any positive pressure ventilation, too much oxygen, and any interruption in chest compressions is bad; chest compressions are more likely to be interrupted with intubation than with extraglottic airway placement; it is possible to intubate during uninterrupted chest compressions; and this may be easier with video laryngoscopy.
However you incorporate these concepts into your resuscitation algorithm is OK, as long as you do. Here in Rio Rancho, NM, we apply the cardiocerebral resuscitation paradigm of initial oxygenation with a non-rebreather alone rather than employing positive pressure ventilation while we focus on early defibrillation and establishing good chest compressions. Once we are ready for positive pressure, we allow one attempt at ETI while CPR is in progress before EGA placement, though many providers appropriately elect to move straight to an EGA. Use of a transport ventilator is encouraged to minimize ventilation rate, and volume and oxygen is titrated down as soon as possible after return of spontaneous circulation. I believe this is one reasonable interpretation and application of the best evidence.
Kudos to Dr. McMullan and all the researchers helping to guide us through the shadows. But we must recognize what the literature can tell us and what it cannot. We do yet not have enough evidence to state conclusively that BMV is better than invasive airway devices nor that one type of invasive device is better than another. It will be exciting when we finally get the answers to these important questions.
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