12 Mar 2008
A new resuscitation approach used on patients who had cardiac arrests outside of the hospital led to higher survival rates than when the standard treatment was used, according to researchers in an article published in JAMA . The new procedure - minimally interrupted cardiac resuscitation (MICR) - is designed to limit interruption of chest compressions and thus increase the chances of survival.
The paper, written by Bentley J. Bobrow, M.D. (Mayo Clinic, Scottsdale, Ariz.) and colleagues, first highlights that cardiac arrest that occurs outside a hospital is a major public health concern and leading cause of death. "Although early defibrillation with automated external defibrillators improves survival, early defibrillation is rare and few patients with out-of-hospital cardiac arrest survive. In 2004, the average survival of patients with out-of-hospital cardiac arrest was 3 percent in the state of Arizona," write the authors.
Formerly called cardiocerebral resuscitation, MICR is used by emergency medical services (EMS) personnel as a new way to treat out-ofhospital cardiac arrest. The technique is designed to use a series of coordinated interventions that maximize blood flow to the heart and brain. These interventions include:
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200 uninterrupted chest compressions,
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Rhythm analysis with a single shock,
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200 immediate post-shock chest compressions before pulse check or rhythm re-analysis,
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Early administration of epinephrine - heart-stimulating adrenaline, and
Delayed endotracheal intubation - ventilating the lungs with a flexible plastic tube in the trachea (wind pipe).
The focus of the investigation was to see whether MICR would improve survival from out-of-hospital cardiac arrest. Bobrow and colleagues analyzed a sample of patients with out-of-hospital cardiac arrests in two metropolitan cities in Arizona both before and after MICR training of fire department emergency medical personnel. A second part of the study, designed to test protocol compliance, analyzed patients who actually received MICR from the two metropolitan cities and 60 additional fire departments in Arizona. These patients were compared to ones who received standard advanced life support instead of MICR.
Survival-to-hospital discharge increased from 1.8% in the before MICR training group to 5.4% in the after MICR training group among the
886 patients with cardiac arrest in the two cities. A subgroup of 174 patients had a witnessed cardiac arrest and ventricular fibrillation increased survival from 4.7% in the before MICR training group to 17.6% in the after MICR training group.
Ventricular fibrillation is a condition of chaotic, irregular heart rhythm that leads to little or no blood circulation but may respond to defibrillation.
Overall, the survival-to-hospital discharge rate for those who did not receive MICR as 3.8%, whereas for those who did receive MICR, the rate was 9.1%. The protocol compliance analysis also resulted in a rate of survival with witnessed ventricular fibrillation and cardiac arrest of 11.9% who did not receive MICR and 28.4% who received MICR.
The authors discuss: "Why should MICR be associated with improved outcomes after out-of-hospital cardiac arrest? One major contributor to the poor survival rates of patients with out-of-hospital cardiac arrest is prolonged inadequate myocardial and cerebral perfusion. During resuscitation efforts, the forward blood flow produced by chest compressions is so marginal that any interruption of chest compressions is extremely [harmful], especially for favorable neurological outcomes. Excessive interruptions of chest compressions by pre-hospital personnel are common. Therefore, MICR emphasizes uninterrupted chest compressions."
"In this study, survival-to-hospital discharge of patients with an out-of-hospital cardiac arrest improved significantly after implementation of
MICR as an alternate EMS protocol. These findings require confirmation in randomized trials," conclude Bobrow and colleagues.
An accompanying editorial, written by Mary Ann Peberdy, M.D., and Joseph P. Ornato, M.D., (Virginia Commonwealth University,
Richmond), comments on the MICR protocol:
"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. Progress in improving survival after cardiac arrest is most commonly made by a gradual evolution of science and its translation into clinical medicine rather than single, earth-shattering revolutions. This study represents confirmation that the quality of CPR, particularly the need for minimally interrupted chest compression and the lesser importance of positive pressure ventilation [receiving oxygen under pressure by a mechanical respirator], is a meaningful development in the evolution of resuscitation science."
Minimally Interrupted Cardiac Resuscitation by Emergency Medical Services for Out-of-Hospital Cardiac Arrest
Bentley J. Bobrow, MD; Lani L. Clark, BS; Gordon A. Ewy, MD; Vatsal Chikani, MPH; Arthur B. Sanders, MD; Robert A. Berg, MD; Peter B.
Richman, MD; Karl B. Kern, MD
JAMA. (2008). 299(10):1158-1165.
Click Here to View Abstract