The Trip Report: OHCA Survival: Is It Improving Or Not?
Reviewed This Month
Multistate 5-Year Initiative to Improve Care for Out-of-Hospital Cardiac Arrest: Primary Results From the HeartRescue Project
Authors: van Diepen S, Girotra S, Abella BS, et al.
Published in: J Am Heart Assoc, 2017 Sep 22; 6(9).
This month we discuss an interesting study recently published in the Journal of the American Heart Association. This is a fantastic manuscript—before now we really didn’t have many studies that evaluated data on very large patient populations. Most use data from studies of regions, communities, or research networks (which are essentially collaborative agreements between hospitals, EMS agencies, and/or universities across regions, states, and sometimes countries to work together on specific research initiatives).
While these studies contribute to our overall knowledge on their topics, their results often aren’t generalizable. In other words, the results represent just that studied population, and we can’t assume they would be the same if the study were performed in another location or with a different population. This is likely one of the reasons why the Institute of Medicine called for the development of a nationally representative cardiac arrest registry.
This study examined data from the Cardiac Arrest Registry to Enhance Survival (CARES). Some of you reading this likely have entered data into CARES. CARES collects data from dispatch, EMS, and hospitals about out-of-hospital cardiac arrest (OHCA) patients. One of the most impressive aspects of CARES is that data is linked, so we can understand what happens to OHCA patients throughout the continuum of care.
This study used data from Arizona, Minnesota, North Carolina, Pennsylvania, and Washington, the first five states to collect CARES data. The study period was from January 1, 2011 to December 31, 2015. Patients eligible for inclusion were adults in a pulseless state from a presumed cardiac etiology. Arrests could not be due to trauma, and the patient had to have received CPR by EMS and/or defibrillation or a shock from an AED.
All OHCA rhythms were assessed. The authors also separately assessed a subgroup of patients that had bystander-witnessed OHCAs with initially shockable rhythms. This was called the Utstein subgroup.
There were a few outcomes of interest. First the authors wanted to understand the percentage of total OHCA cases they were capturing with CARES data. They did this by first estimating how many OHCAs they believed occurred in each state based on population; then they divided the number of OHCA cases in the CARES registry by this estimate to calculate the percentage. The authors also wanted to evaluate whether bystander CPR was provided, whether a bystander applied the AED, if targeted temperature management was performed, if the patient survived to hospital discharge, and if the patient had good functional status at hospital discharge.
To address their outcomes of interest, the authors used a variety of statistical methods. They calculated descriptive statistics, used linear and logistic regression, and performed a Mantel-Haenszel test of trend. We lack space in this column to explain each of these tests, but based on the types of data available and the study objectives, they appear to be the appropriate statistical tests.
During the study period there were 66,306 patients treated for OHCA. There were 1,318 patients who were excluded from the study either because they were less than 18 years old (1,165) or didn’t have survival data available (153). Those with missing outcome data were younger, had bystander- or EMS-witnessed OHCAs in public locations, and had initial shockable rhythms. Remember this; it will help put these results into context.
In total 64,988 patients were included in the all-rhythm OHCA population, and 10,046 patients in the Utstein subgroup. The overall population was mostly male (62.9%), with a median age of 65.7 years. Overall 41.2% of the OHCAs were witnessed by a bystander.
Some of the results were pretty encouraging: From 2011 to 2015 there was more than a twofold increase in the percentage of OHCA cases captured in the CARES registry (39.0% to 89.2%). So, all of you who have been diligently entering data into CARES, well done! Keep up the good work.
Over the entire study period, the rate of bystander CPR was 42.8%, and bystanders applied AEDs on 4.6% of OHCAs. AEDs were applied by someone (bystander, police officer, or other first responder) before EMS arrived in 21.9% of OHCAs. Targeted temperature management was performed for 36.5% of all patients and 55.4% of the Utstein subgroup.
For the all-rhythm OHCA group, the unadjusted (unadjusted simply means they calculated the percentage without making any statistical adjustments for other important or confounding variables) percentage who survived to hospital discharge was 11.4%, and the percentage discharged with good cerebral performance was 9.4%. For the Utstein subgroup the numbers were better, with 34.0% surviving to hospital discharge and 30.4% being discharged with good cerebral function.
Here is where the results get less encouraging: When the authors looked for changes over time in the all-rhythm group, the unadjusted percentage surviving to hospital discharge actually decreased. In 2011 this percentage was 13.7%, and in 2015 it was 10.5%. This was statistically significant, with a p-value less than 0.001 (a p-value of less than 0.05 is typically considered statistically significant). The percentage with good cerebral function at hospital discharge also decreased from 10.4% to 8.9% (p=0.002), but after logistic regression adjustment that decrease was no longer statistically significant (p=0.08).
The Utstein group did not see a statistically significant difference in the percentage of survival to hospital discharge (34.7% to 34.6%, p=0.84) or in good cerebral function (28.5% to 31.5%, p=0.42). This remained statistically insignificant after logistic regression.
Those last two paragraphs basically say that from 2011 to 2015, there was no change in survival or the percentage discharged with good cerebral function. Initially that seems somewhat unbelievable, with all the time and effort we put into improving outcomes for OHCA patients. However, remember whose survival data was missing: The patients without it were often younger, had witnessed arrests in public, and had shockable rhythms. There were only 153 of these patients, but they’re the ones most likely to have good outcomes.
Still, it looks like we have more work to do to improve outcomes for OHCA patients. And what better time to identify things we can improve than the start of a new year? While there are some limitations here (as there are with all studies), this paper is extremely important because it provides a clear picture of where we are. Try to read this manuscript in its entirety—it has a lot of important and interesting information, including supplemental tables. Happy new year, everyone!
Antonio R. Fernandez, PhD, NRP, FAHA, is research director at the EMS Performance Improvement Center and an assistant professor in the Department of Emergency Medicine at the University of North Carolina–Chapel Hill. He has been a nationally certified paramedic since 2005 and completed the EMS Research Fellowship at the National Registry of Emergency Medical Technicians.