Cooling Out-of-Hospital Cardiac Arrest Patients Improves Outcomes
Implementing a regional system for administering therapeutic hypothermia to out-of-hospital cardiac arrest patients results in lower mortality and increased neurological recovery, according to findings published online July 11, 2011, ahead of print in Circulation. The therapy is typically begun during ambulance transport and can continue seamlessly through transfer to the emergency department or, when necessary, the cath lab.
Researchers led by Michael R. Mooney, MD, of the Minneapolis Heart Institute Foundation (Minneapolis, MN), developed an initiative to establish therapeutic hypothermia as the standard of care for resuscitated cardiac arrest patients throughout Minnesota in the hopes of combatting the high mortality rates and common neurological complications that occur with such cases. First responders in the region around Abbott Northwestern Hospital in Minneapolis collaborate to initiate cooling via ice packs during initial EMS transport to the emergency department at network hospitals. The goal is to reduce the core temperature to 33 degrees Celsius within 2 to 4 hours and maintain that level for about 24 hours, gradually rewarming patients after this point until the core temperature returns to normal.
At the hospital, a device is used to draw chilled water through hydrogel pads placed on the torso and lower extremities (Arctic Sun, Medivance, Louisville, CO). Patients presenting with STEMI are transferred directly to the cath lab, where angiography/PCI and cooling are performed simultaneously.
Short Time to Big Chill Improves Survival
The researchers followed 140 consecutive cardiac arrest patients treated with therapeutic hypothermia between February 2006 and August 2009. About three-quarters of the patients presented at non-cooling hospitals and were transferred to Abbott Northwestern, with an average transport distance of 56 miles. In 43% of patients, initial cooling was applied before arrival at Abbott Northwestern. Median time from arrest to return of spontaneous circulation was 22 minutes, and median time between return of circulation and application of the cooling device was 117 minutes.
Overall survival to hospital discharge was 56%, with 92% of survivors discharged with a positive neurological outcome. Survival was similar in transferred (57%) and nontransferred (52%) patients. Nonventricular fibrillation arrest and presence of cardiogenic shock were strongly associated with mortality, but survivors with these characteristics had high rates of positive neurological recovery at 100% and 89%, respectively.
When the elapsed time between return of circulation and application of the cooling device at Abbott Northwestern lasted more than 2.5 hours, patients were 63% less likely to survive to discharge than when that time remained under 1.5 hours. Overall, there was a 20% increase in mortality risk (95% CI 1.04-1.39) for every hour of delay to the initiation of cooling. In addition, among survivors characterized by the longest times to cooling, normal or near-normal neurological function was preserved in 95% to 100%.
Cooling in the Cath Lab
Approximately half (49%) of the patients presented with STEMI and received therapeutic hypothermia in the cath lab. Almost three-fourths (72%) of all patients received angiography and 40% received PCI. STEMI patients actually fared better than those without STEMI, showing a higher likelihood of survival (OR 2.05; 95% CI 1.04-4.04). Those who received emergency angiography also showed a higher likelihood of survival, whether they did (OR 2.13; 95% CI 0.93-4.91) or did not (OR 3.54; 95% CI 1.44-8.74) receive PCI, though the former association was just a trend.
Over the 4 years of the program, substantive gains in efficiency were achieved. For instance, the median time between return of circulation and attainment of target core temperature was lowered by nearly 90 minutes (345 to 258 minutes), and the median time from return of circulation to first cooling was lowered by 2 hours (161 to 35 minutes), reflecting improvements in efforts to initiate early cooling. In addition, the proportion of cases receiving at least some cooling prior to arrival at Abbott Northwestern rose consistently each year, from 6% in year 1 to 69% by year 4, while the elapsed time between patient arrival in the emergency department and application of the cooling device was dramatically reduced from a median of 96 minutes to a median of 20 minutes.
“We have demonstrated that simple cooling with ice bags initiated soon after arrest can be associated with incrementally improved outcomes, even if transfer to a specialized [therapeutic hypothermia] center is required, and that [therapeutic hypothermia] is an achievable standard of care that can be applied in urban and rural settings equally where regional systems of care have been developed,” the authors write.
Patient Transfer Procedures Key
Dr. Mooney and colleagues stress a few key components for expanding access to therapeutic cooling, such as capitalizing on established emergency care networks with refined patient transfer processes and using protocols that include prehospital cooling. In addition, they stress that with careful planning, “[therapeutic hypothermia] and PCI for STEMI can be achieved concurrently without delay to either. This is crucial given that a significant proportion of [out of hospital arrest] patients who survive to admission will have STEMI requiring timely PCI.”
According to Ajay J. Kirtane, MD, SM, of Columbia University Medical Center (New York, NY), although the study was not randomized, the results are nevertheless impressive. “The overall survival with [positive] neurologic outcome appears to be quite good,” he told TCTMD in an e-mail communication. He added, though, that there are some obstacles to setting up such networks. “These systems may be the best way to provide care for the greatest number of patients, but they take a lot of ‘activation energy,’ with buy-in from physicians, hospitals, and the states. Even after the ‘buy-in’ phase, they can take a lot of work to set up,” he said.
But in terms of making them work, “the hub-and-spoke model is somewhat critical, with continuous QA and feedback,” Dr. Kirtane said. “What seems to have made this particularly successful here is grafting the hypothermia protocol on top of a well-known and existing regional STEMI network.”
Cooling Hits New York
And adopting such measures in the cath lab is not that burdensome, he noted. “This particular device isn't that difficult to use, and in fact can be started in the emergency room, or even potentially in the field,” Dr. Kirtane said. “In New York, there is currently an ongoing initiative to try to broaden the use of cooling to patients with out-of-hospital cardiac arrest, without significant difficulties to the cath lab.”
However, training and additional data on clinical outcomes are important, he cautioned. “The [post-therapeutic hypothermia] management can sometimes be complicated, and some degree of advanced training is required,” Dr. Kirtane stressed. “Additionally, there are data that suggest that even without ST elevation, a significant proportion of patients with out of hospital [ventricular tachycardia/ventricular fibrillation] have significant CAD, and some are advocating early angiography for these patients as well. At this time, we need more data to see how outcomes [in such patients] are influenced by [therapeutic cooling].”
Mooney MR, Unger BT, Boland LL, et al. Therapeutic hypothermia after out-of-hospital cardiac arrest: Evaluation of a regional system to increase access to cooling. Circulation. 2011;Epub ahead of print.
- The study was supported by the Minneapolis Heart Institute Foundation.
- An unrestricted grant provided by Medivance was used to support data collection.
- Drs. Mooney and Kirtane report no relevant conflicts of interest.