Bobrow BJ, Clark LL, Ewy GA, et al. Minimally interrupted cardiac resuscitation by emergency medical services for out-of-hospital cardiac arrest. JAMA 299(10):1,158–65, 2008.
The objective was to investigate whether the survival of patients with out-of-hospital cardiac arrest would improve with minimally interrupted cardiac resuscitation (MICR), an alternate EMS protocol.
Design, setting and patients—A prospective study of survival to hospital discharge between Jan. 1, 2005, and Nov. 22, 2007. Patients with out-of-hospital cardiac arrests in two metropolitan cities in Arizona were assessed before and after MICR training of fire department emergency medical personnel. In a second analysis of protocol compliance, patients from the two metropolitan cities and 60 additional fire departments in Arizona who received MICR were compared with patients who did not receive MICR but received standard advanced life support.
Intervention—Instruction for EMS personnel in MICR, an approach that includes an initial series of 200 uninterrupted chest compressions, rhythm analysis with a single shock, 200 immediate post-shock chest compressions before pulse check or rhythm reanalysis, early administration of epinephrine, and delayed endotracheal intubation.
Main outcome measure—Survival to hospital discharge.
Results—Among the 886 patients in the two metropolitan cities, survival to hospital discharge increased from 1.8% before MICR training to 5.4% after. In the subgroup of 174 patients with witnessed cardiac arrest and ventricular fibrillation, survival increased from 4.7% before MICR training to 17.6% after. In the analysis of MICR protocol compliance involving 2,460 patients with cardiac arrest, survival was significantly better among patients who received MICR than those who did not (9.1% vs. 3.8%). This was also true of patients with witnessed ventricular fibrillation (28.4% vs. 11.9%).
Conclusions—Survival to hospital discharge of patients with out-of-hospital cardiac arrest increased after implementation of MICR as an alternate EMS protocol. These results need to be confirmed in a randomized trial.
Chest compressions and circulation are increasingly being recognized as the most important parts of CPR. Over the last several CPR guidelines, we have seen the ratio of compressions to ventilations go from 5:1 to 15:2 to 30:2. This study, along with a number of others in both animal and human patients, suggests that the optimal ratio may be even higher—especially in the first few minutes, when ventilations may not be needed at all.
There are several limitations to this study. First, many of the MICR patients may have received ventilations during the 200 compressions, as that was allowed in the protocols, so this is not truly a study of "chest compression only" CPR. Second, before starting MICR many providers were following the 2000 guidelines (with a 15:2 ratio, early endotracheal intubation and three stacked defibrillations, with long pauses in CPR), so we cannot say how MICR compares to the 2005 guidelines (hard and fast compressions with minimal interruption, single shock, delayed intubation). And third, by the end of the two-year MICR interval, survival rates decreased to pre-MICR levels, which calls into question whether the improvements can be sustained.
But the most important message from this study is that we can do considerably better than we do now, and substantially increase our patients' likelihood of survival. Whether it was the compressions-only approach, the quality of the compressions (which we know are often poor and would expect to be better with more attention and training), the reduction in CPR interruptions, the early epinephrine or a combination, this gives us a reason to carefully examine and improve our approach to resuscitation.