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Myths in Emergency Medicine

Outcomes Worse for Intubated OHCA Patients

Spiegel, Rory, MD

doi: 10.1097/01.EEM.0000547689.28595.f7
Myths in Emergency Medicine

Dr. Spiegel is a clinical instructor in emergency medicine and a critical care fellow in the division of pulmonary and critical care medicine at the University of Maryland Medical Center. Visit his blog at http://emnerd.com, follow him on Twitter @emnerd_, and read his past articles at http://bit.ly/EMN-MythsinEM.

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Airway has been paramount to managing cardiac arrest since the earliest endeavors in resuscitation—the use of tobacco smoke enemas to resuscitate drowning victims on the banks of the Thames was documented as far back as 1746. (Lancet 2002;359[9315]:1442.) Such efforts, while anatomically misplaced, were well intended in principle. We have since discovered alternative preferred orifices through which to ventilate our patients with cardiac arrest, but the exact conduit to deliver these artificial breaths is still unclear.

A growing body of evidence suggests that de-emphasizing early definitive airway management may lead to improved outcomes. The majority of these data was observational and prone to the biases associated with such analyses. (Resuscitation 2015;93:20.) Two recently published major trials now give us high-quality data on the role of a definitive airway in managing patients with out-of-hospital cardiac arrest (OHCA).

The first of these studies, the Pragmatic Airway Resuscitation Trial (PART), was a multicenter cluster-crossover randomized trial in which 27 EMS agencies across the United States were randomized to one of two initial advanced airway strategies, laryngeal tube (LT) or endotracheal tube (ETI) insertion. (JAMA 2018;320[8]:769.) The trial protocol did not limit the number of attempts permitted by paramedics, nor did they dictate the rescue strategies used for a failed airway. The participating EMS personnel followed local protocol to confirm airway placement and OHCA management, including terminating resuscitation efforts in the field.

A total of 3,004 patients were enrolled over a two-year period, 1,505 to the LT group and 1,499 to the ETI group. Compliance with the treatment strategy (defined as the initial attempt with assigned airway or use of BVM only) was high in both groups, 95.5 percent and 90.7 percent, respectively. Success of the initial strategy utilized was significantly higher in the LT group at 90.3 percent compared with only 51.6 percent in the ETI group. The authors reported a statistically significant difference in their primary outcome, survival at 72 hours: 18.3 percent in the LT group v. 15.4 percent in the ETI group.

This survival benefit favoring the LT group remained consistent when the authors examined survival to hospital discharge (10.8% v. 8.1%) and survival with a good neurological outcome, defined as an mRS of 0-3, (7.1% v. 5.0%). The authors also reported higher rates of airway insertion attempts (18.9% v. 4.5%), unsuccessful initial airway insertions (44.1% v. 11.8%), unrecognized airway misplacement or dislodgement (1.8% v. 0.7%), pneumothoraces (7.0% v. 3.5%), and rib fractures (7.0% v. 3.3%) in the ETI group compared with the LT group. These outcomes remained consistent when the authors examined subgroups based on initial rhythm and whether the event was witnessed.

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Statistical Noise?

These results seem to vindicate those of us who advocate for a supraglottic approach to airway management in cardiac arrest. The lower rates of neurologically intact survival may well represent the logistical burdens associated with definitive airway management in patients in cardiac arrest. But, as with any study, these small differences are also likely to represent statistical noise, and a larger sample size may demonstrate a regression to the true mean. It seems that the PART results represent the latter, as demonstrated by the AIRWAYS-2 trial published alongside it. (JAMA 2018;320[8]:779.) The authors conducted a multicenter, cluster controlled trial that randomized prehospital providers at four large EMS agencies to a second-generation supraglottic airway device or endotracheal intubation using direct laryngoscopy.

A much larger cohort—9,296 patients—experiencing OHCA was enrolled over a two-year period in AIRWAYS-2. The authors found no difference in their primary outcome, survival with a good neurological outcome (mRS 0-3), 6.4 percent in the supraglottic group v. 6.8 percent in the tracheal intubation group.

In the subset of patients who received advanced airway management (80% of the entire cohort), more patients in the supraglottic airway device group had a favorable outcome, 3.9 percent, compared with only 2.6 percent in the endotracheal group. They also noted that a supraglottic airway device treatment strategy was significantly more successful in achieving ventilation after up to two attempts (87.4% vs 79.0%), without noting any difference in regurgitation or aspiration.

Some would argue that the results of these trials compare a strategy that utilizes a supraglottic device with one that employs subpar use of an endotracheal tube. After all, the first-pass success rate reported by the authors in the PART trial was only 51.6 percent. This imperfection itself may be responsible for the inferior outcomes observed in this cohort. This is a valid criticism, but it is unjust to assume that this failure in airway management was due to a poorly trained group of prehospital providers. The results may simply be due to the acuity of the patients and environment in which these providers find themselves operating.

But let's say for argument's sake that it was due to a lack of training and could be solved by intense remediation. To what end? The AIRWAYS-2 trial reported a higher rate of initial ventilation success, demonstrating at best that ETT was no better than a supraglottic approach. It is a zero-sum game. One could invest in intensive mandatory airway training and video laryngoscopy devices on every ambulance throughout a system to drive up the first-pass success rate, but survival would remain unchanged, diverting logistical and financial resources away from the things that actually matter.

These are two well done large cluster-randomized trials examining broad swaths of the population. A substantial portion of the population did not ultimately receive the intended management strategy, but the pragmatic design of these trials represent the realities of the prehospital environment. These trials examine the logistical complexities and subsequent consequences of an intended airway strategy. They are statistically incongruent, but they likely represent the same underlying truth. Managing the airway is of minimal clinical consequence for a large portion of patients experiencing OHCA. It is an unnecessary distraction for the most part, and the most logistically simple management strategy should be undertaken, which is a supraglottic airway in most cases. The question these data left unanswered is how a supraglottic strategy compares with more minimalistic approaches such as a simple nasal cannula and a jaw thrust. Or even the insufflation of more noxious fumes, like tobacco smoke perchance.

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