Research analysis: ‘ECMO is a useful tool but not a magic bullet’

Two studies from the University of Minnesota examine early ECMO and the chain of survival


Two recent studies from the University of Minnesota examined the use of early ECMO in patients who experienced cardiac arrest outside of the hospital. “Advanced reperfusion strategies for patients with out-of-hospital cardiac arrest and refractory ventricular fibrillation” (ARREST) was a phase 2 randomized control trial that included patients aged 36 to 73 years old who experienced cardiac arrest outside of the hospital from August 2019 to June 2020 [1]. A total of 30 patients were included in the trial; 15 were randomized to the early ECMO group therefore were cannulated and taken to the cardiac catherization lab immediately upon hospital arrival, while 15 were randomized to the standard ACLS protocol.

Survival to hospital discharge, cumulative survival, modified Rankin score and cerebral performance category scores were all used to assess outcomes in trial participants. Researchers found that survival to hospital discharge was higher in the ECMO group; 43% vs 7%. Additionally, cumulative survival was much higher in the ECMO group; 43% in 3 and 6 months versus 0% for both time periods in the ACLS group. Subsequently, the trial was ended early because there was a significant benefit to patients in the ECMO group.

Another study, “The Minnesota mobile extracorporeal cardiopulmonary resuscitation consortium for treatment of out-of-hospital refractory ventricular fibrillation: Program description, performance and outcomes” (MMRC) was an observational cohort study that included 63 patients from December 2019 to April 2020 [2]. The MMRC was included hospitals and EMS agencies in the Minneapolis-St. Paul region. The mobile ECMO cannulation teams were comprised of a physician and two assistants who were either nurses, paramedics or physicians. The teams met the patients in the designated emergency department, began ECMO and transferred the patients to the cardiac catherization lab. Survival to discharge, cerebral performance score and long-term survival were analyzed.

Both studies were performed in the same area and had the same inclusion criteria: patients aged 18 to 75, with initial rhythms of either ventricular fibrillation or pulseless ventricular tachycardia, along with failure to achieve ROSC after three defibrillations.
Both studies were performed in the same area and had the same inclusion criteria: patients aged 18 to 75, with initial rhythms of either ventricular fibrillation or pulseless ventricular tachycardia, along with failure to achieve ROSC after three defibrillations. (Photo/Getty Images)

A total of 58 patients were deemed eligible for ECMO cannulation in the field by EMS; 45 ultimately received ECMO (13 were declared dead based on arterial blood gas results). Of the patients who were cannulated, 27 survived to discharge (60%) and 25 survived to 3 months (56%). The average cerebral performance score was 1.6 at discharge and 1.3 at 3 months.

Both studies were performed in the same area and had the same inclusion criteria: patients aged 18 to 75, with initial rhythms of either ventricular fibrillation or pulseless ventricular tachycardia, along with failure to achieve ROSC after three defibrillations. Patients were disqualified if their body habitus couldn’t accommodate a Lund University Cardiopulmonary Assist System (LUCAS) or if transfer time to the emergency department exceeded 30 minutes. There was no overlap in participants between the two studies.

Patients weren’t cannulated for ECMO and resuscitation efforts were stopped if two of the following were met: ETCO2 < 10 mmHg, PaO2 < 50 mmHg or oxygen saturation < 85% and lactic acid > 18 mmol/L. After the initial resuscitation period, patients in both groups received the same standard of post-resuscitation care, which included therapeutic hypothermia and cardiac ICU admission.

Top quotes from ECMO research

These quotes stand out from the research:

“The ARREST trial outcomes reflect the importance of a highly orchestrated collaboration and coordinated implementation of the chain of survival throughout a community.” — Demetris Yannopoulos

“Refractory VF/VT OHCA is most often associated with severe coronary artery disease and acute occlusion with minimal survival unless treatment is provided to reverse the underlying, presumably causative, pathophysiology.” — Jason Bartos

“Each component of care is crucial and significantly contributes to survival.” — Jason Bartos

Three Takeaways on early use of ECMO

Following are three takeaways from the two Minnesota ECMO studies.

1. Early ECMO helps survival

Based on the results of the ARREST trial, initiating ECMO early leads to better survival and patient outcomes. Of the 15 patients in the standard ACLS group, only 1 survived to discharge and then died less than 3 months later. Of the 15 patients in the early ECMO group, 6 survived to discharge and to 6 months. The ARREST trial was even stopped earlier than planned because there was such a clear benefit for patients in the early ECMO group.

Similarly, the MMRC study had 47% survival to discharge in the patients who were ECMO eligible (60% survival in those who were cannulated). Past studies by this same group have shown that survival to discharge rates in the same clinical scenario have been 8.2% and 23% with standard ACLS resuscitation.

2. Early ECMO leads to better functional status on discharge

In the ARREST trial, patients in the ECMO arm had much better neurological outcomes when compared to the one patient in the ACLS arm. ECMO patients had an average cerebral performance category (CPC) of 2.5 at discharge and 1.16 at 6 months. CPC scores less than 3 are associated with a good neurological outcome and greater chance of long-term survival. The one patient in the ACLS group had a CPC of 4 at discharge.

In the MMRC study, CPC scores were even better for ECMO patients, an average of 1.6 at discharge and 1.3 at three months.

3. System, not technology

Both studies emphasized the importance of all parts of resuscitation. ECMO is a useful tool but not a magic bullet. Dispatch, response time, proper CPR, patient transport and ED team coordination are a few of the many parts of the system that gets the patient to where they need to be for possibly starting ECMO. If any part of these breaks down, the patient may not even make it to the point where cannulation could improve their outcome.

Read next: ECMO in EMS: How to recognize and mitigate extracorporeal membrane oxygenation complications during EMS transport

References

  1. D. Yannopoulos et al. Advanced reperfusion strategies for patients with out-of-hospital cardiac arrest and refractory ventricular fibrillation (ARREST): a phase 2, single centre, open-label, randomised control trial, Lancet (2020).
  2. J.A. Bartos et al. The Minnesota mobile extracorporeal cardiopulmonary resuscitation consortium for treatment of out-of-hospital refractory ventricular fibrillation: Program description, performance, and outcomes, EClinicalMedicine (2020).

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