Streamlined "CPR" by EMS can improve survival in out-of-hospital cardiac arrest

March 12, 2008

Chicago, IL - Patients resuscitated from cardiac arrest by emergency medical services (EMS) personnel are three times more likely to survive to hospital discharge when CPR follows a streamlined protocol calling for up to three uninterrupted two-minute series of chest compressions and little in the way of assisted ventilation, compared with conventional resuscitation methods, suggests a prospective study[1].

The technique, which the authors call "minimally interrupted cardiac resuscitation" (MICR) and is aimed primarily at restoring blood flow to the heart and brain, appeared especially effective among patients with witnessed cardiac arrest and documented VF—that is, a shockable rhythm, report the authors in the March 12, 2008 Journal of the American Medical Association.

"In essence we try to minimize all interruptions to chest compression," lead author Dr Bentley J Bobrow (Mayo Clinic, Scottsdale, AZ) told heart wire .

"We take out the interruptions from early endotracheal intubation, repeated pulse checks, rhythm analysis, and other procedures like central line placement that we used to have and replace them with high-quality chest compressions," he said. "What I mean by that is rapid, forceful chest compressions allowing full chest recoil. And while we maximized the chest-compression component, we taught providers to minimize the ventilation component."

Conducted throughout Arizona, the study evaluated MICR in two ways, first by comparing resuscitated cardiac-arrest outcomes before and after EMS personnel in two metropolitan areas were trained in the technique, and also across different EMS districts with personnel trained or not trained in MICR.

What we have shown is that with very simple protocol changes on a systemwide basis, you can improve meaningful neurologic survival.

Learning the technique didn't involve unusual challenges, according to Bobrow. "There are no new procedures. It's just reprioritizing them," he said. "What we have shown is that with very simple protocol changes on a systemwide basis, you can improve meaningful neurologic survival."

In an accompanying editorial[2], Drs Mary Ann Peberdy and Joseph P Ornato (Virginia Commonwealth University, Richmond) note that, despite the study's acknowledged limitations, "there is an important take-away message: outcomes for resuscitating patients in cardiac arrest remain dismal, yet significant improvements are possible."

As described by Bobrow et al, MICR calls for an initial 200 uninterrupted chest compressions over two minutes, followed by a rhythm analysis and, if necessary, a single defibrillator shock, "immediately followed by 200 postshock chest compressions before any pulse check or rhythm reanalysis." Three sequences of 200 chest compressions are required before the victim can be intubated.

A milligram of IV epinephrine is given "as soon as possible during the protocol and again with each cycle of chest compressions and rhythm analysis."

According to the group, "early and excessive" ventilation is discouraged in MICR, which calls for "passive oxygen insufflation with the placement of an oral-pharyngeal airway, a nonrebreather face mask, and high-flow oxygen rather than positive-pressure ventilation." But because that approach was "such a dramatic change for the EMS personnel," the study allowed MICR to include conventional bag-valve-mask ventilation.

What the team has developed is what we call the 'NASCAR' model of resuscitation. The providers rotate around the victim in a very coordinated way to minimize all interruptions to chest compression.

Typically, there is a lot of variation in how EMS providers in different districts around the US apply advanced life-support measures in out-of-hospital cardiac arrest, Bobrow explained. For example, he said, shocks may be administered before or after the initiation of chest compressions, endotracheal intubation is started either earlier or later in the process, and epinephrine may be among the last steps taken.

"Our thought is that providers shouldn't focus on the advanced airway techniques right off the bat," Bobrow said. "That leaves another provider, hopefully, to administer epinephrine as early as possible. We believe if epinephrine helps in resuscitation at all, it's got to be given early and not late."

Actually, he observed, one of the benefits of the MICR protocol is that there is a detailed protocol at all. "What is standard resuscitation? It's really hard to say, because it's different everywhere." The MICR protocol even provides a model for how providers should position themselves during the procedure. "Each provider does the chest compressions, or the airway, or the rhythm analysis, and then they switch." That's partly because an individual is likely to fatigue after performing 200 compressions, Bobrow explained, "and then the quality of the compressions goes down."

What the team has developed, Bobrow said, "is what we call the 'NASCAR' model of resuscitation. The providers rotate around the victim in a very coordinated way to minimize all interruptions to chest compression."

The first part of the study centered on 886 arrest victims managed by EMS personnel either before or after MICR training; the intention-to-treat analysis assumed that all MICR-trained personnel accurately followed the MICR protocol.

Of the 218 patients managed before MICR training, 1.8% survived to hospital discharge, as compared with 5.4% of the 668 patients managed after training. Among the subgroup of 174 patients with witnessed arrest and a shockable rhythm, the rate increased from 4.7% before to 17.6% after MICR training.

Adjusted odds ratio (95% CI) for survival to hospital discharge

Population After vs before MICR training MICR vs non-MICR
All cases 3.0 (1.1-8.9) 2.7 (1.9-4.1)
Witnessed arrest, shockable rhythm 8.6 (1.8-42.0) 3.4 (2.0-5.8)

The study's second phase involved the same two EMS districts plus 60 others; personnel in 12 of the 62 districts had been trained in MICR, and those in the remaining districts had no experience with the technique. In this analysis comparing MICR-based resuscitation with non-MICR resuscitation, resuscitation efforts qualifying as MICR had to be aimed at delivering four key components: 200 preshock compressions, 200 postshock compressions, endotracheal intubation only after a third sequence of 200 compressions, and IV epinephrine during the first or second compression sequence.

Of the 1799 victims who did not receive MICR and the 141 who did, 3.8% and 9.1% survived to hospital discharge. The corresponding rates among the subgroup with witnessed arrest and a shockable rhythm were 11.9% and 28.4%.

Interestingly, in the analysis comparing outcomes before and after MICR training, the rate of survival to hospital admission was about 16% in both groups, while survival to discharge—the study's primary end point—was superior with MICR, Bobrow et al observe. That suggests, they write, that the patients were initially resuscitated at about equal rates whether or not MICR was performed, but it was MICR that promoted organ perfusion sufficient for survival to discharge.

"Although the concept of MICR needs further scientific evaluation, perhaps in the form of a randomized, controlled, clinical trial with precise documentation of protocol compliance, these details are likely not important factors to the numerous additional survivors who are back home with their families after the implementation of this new protocol," according to Peberdy and Ornato.

The trial, along with other research, they write, "represents confirmation that the quality of [resuscitation], particularly the need for minimally interrupted chest compression and the lesser importance of positive-pressure ventilation, is a meaningful development in the evolution of resuscitation science."


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