This month we look at the most recent cardiac arrest paper from the Resuscitation Outcomes Consortium (ROC). This impressive group has been making great strides in collecting data across many U.S. agencies, and their dedication to prehospital scientific research is undoubtedly the largest, longest running, and best coordinated EMS research effort to date.
Background: In this study, ROC set up a cluster-randomized trial to scientifically evaluate the effectiveness of continuous chest compressions (i.e., hands-only CPR) vs. compressions interrupted for ventilations at a ratio of 30:2 on clinical outcomes of out-of-hospital cardiac arrest (OHCA) patients. Previous studies determining the effectiveness of CPR delivery methods have demonstrated higher OHCA survival rates with continuous compressions vs. interrupted compressions. Unfortunately, this research was only correlational, showing that improved survival and continuous compressions were associated, but not necessarily causal.
What we already know: Interruption of chest compressions has been associated with decreased survival in animal models—not humans—and continuous compressions are associated with improved neurological outcomes except in cases of hypoxic arrest.
What this study adds: Confirmation that high-quality compressions, short interruptions, teamwork, data gathering and analysis are all markers of high-performing EMS systems with improved OHCA outcomes. Hospital care, etiology, and other variables must be controlled if we’re to make progress on identifying specific interventions.
Methods: Between June 6, 2011, and May 28, 2015, patients in the 114 participating EMS agencies were randomly assigned to either an intervention group (continuous chest compressions at 100/min with 10 ventilations/minute = 12,653 patients) or to a control group (compressions interrupted for ventilations = 11,058 patients). Outcomes were assessed using a modified Rankin scale, from 0-6, with ≤ 3 reflecting favorable neurological function.
Outcome measures included: 1) rate of survival to discharge; 2) neurologic function at discharge; 3) adverse events; and 4) hospital-free survival days (number of days alive and out of the hospital during the first 30 days following arrest).
Results: The study found no statistical difference between either group’s rate of survival to discharge (9.0% of the continuous compressions group, 9.7% of the 30:2 group). Seven percent of the continuous compressions group and 7.7% of the 30:2 group survived with a modified Rankin score of 3 or less, but these results didn’t achieve a statistically significant difference (p = .09). Also important was the compression-only group was significantly less likely to be transported or admitted to the hospital, and this group also had shorter hospital-free survival.
Discussion: The results of this paper have been long awaited as we continue to question current practiceand search for treatments that really matter in OHCA outcomes.
It’s important to note that a large study with many contributing sites has many variables that can mask important details. OHCA is the result of several vastly different clinical conditions (e.g., coronary occlusion, pulmonary embolus, trauma, etc.). It’s a big leap of faith to study these patient groups together, looking for outcome differences from a single element, in this case CPR style.
Selection of patients is an important limiting factor in this study. Excluded patient groups included EMS-witnessed arrest, traumatic arrest, hypoxic arrest, hemorrhagic exsanguination, pregnancy, prisoners, pre-existing tracheostomy, mechanical chest compressions prior to manual CPR, and many more.
In-hospital care for study patients (e.g., targeted temperature management, heart catheterization), including many treatments associated with OHCA outcomes, wasn’t controlled.
Interestingly, the interruptions in compression delivery were surprisingly similar for both groups. And for both groups, the compression fraction (i.e., time on chest) was higher than you’d see in other systems, making widespread generalization of the findings more difficult.
Overall, this study supports the concept that chest compressions are only part of the bundle of effective care for OHCA. As the authors appropriately suggest, other factors affecting success may include process elements such as passive ventilation, team coordination, improved care systems management, and CPR performance measurement/feedback devices, to name a few.
Although this paper is an excellent example of progress in EMS research, and this type of work is critical as we tease apart the subtle differences in management of complex patients, it’s important that we pause and recognize the limited conclusions we can reach.