“In 2002, two studies were published in The New England Journal of Medicine demonstrating improved survival and neurologic outcomes when applying therapeutic hypothermia for ‘comatose’ survivors of SCA,” said Patrick “PJ” Flaherty, III, DO, an interventional cardiologist at Arkansas Heart Hospital. “These are the studies that established the goal temperature range, as well. The Hypothermia after Cardiac Arrest Study Group showed pretty convincingly that this range of therapeutic hypothermia provided significant improvement in functional recovery at hospital discharge and lower six-month mortality compared with those who did not receive this type of therapy.”

Not all cardiac patients are appropriate candidates for these protocols as they are not without problems of their own. Some patients are already hypothermic at presentation. Flaherty said the target population that benefits from the hypothermia therapy primarily includes the large number of adult patients who experience out-of-hospital SCA, primarily due to ventricular fibrillation and ventricular tachycardia, who have return of spontaneous circulation (ROSC), but have neurologic impairment at the time of initial presentation.

Therapeutic hypothermia can be achieved with external cooling methods such as cold packs, ice, cold saline infusion, cooling blankets, gastric lavage, surface cooling helmets and peritoneal infusion of cold fluids. The external method is considered to have limitation in that it is labor intensive and clinically inefficient.

A newer option is intravascular temperature management  (IVTM). The Arkansas Heart Hospital is currently making plans to become the first hospital in the state to offer IVTM. There are a couple of different systems on the market being evaluated by the Arkansas Heart Hospital. The current system under review is the Alsius IVTM system by ZOLL.

IVTM is an internal, catheter-based therapy, also referred to as endovascular heat-exchange systems.

“These cooling catheters are introduced percutaneously into the central venous system,” Flaherty said. “Heat exchange then occurs internally as a coil with a large surface area interfaces with the blood passing over the outer surface of the catheter. Overall, these catheters facilitate faster hypothermia induction, more consistent maintenance of goal temperature and a more predictable re-warming phase compared with other modalities of therapy. The control units allow for a specific goal of 33 degrees Celsius to be programmed in, allowing for extremely tight control. Another benefit is that this modality is associated with less shivering than external cooling. Shivering produces heat, which may lead to temperature variability, along with the potential for patient discomfort.”  

As with any treatment for SCA, treatment has the best results when started as soon as possible.

“If possible, the therapy can and should be started in the emergency department while cardiac teams are being scrambled,” Flaherty said. “Treatment can be continued throughout cardiac catheterizations and any rescue or primary percutaneous coronary interventions that might follow. The goal is to achieve the target temperature as quickly as possible. In most cases, this is going to be achieved within three to four hours of therapy initiation, with a target therapeutic temperature range of 32-34 degrees Celsius. The typical normal body temperature is around 37 degrees Celsius.”

In most cases, this is not a prolonged protocol. It is recognized that the optimal cooling period for humans probably has yet to be defined.

“In all likelihood, it varies with the length of the arrest period,” Flaherty said. “Longer arrest typically increases neurologic compromise. Some animal models have suggested longer periods of hypothermia might be more beneficial. Most institutions have adopted a 24-hour therapeutic cooling period, including the 3-4 hours it takes to reach goal temperature. After that, a slow re-warming phase begins.”

While the current primary indication for this therapy is the comatose survivor of SCA with ROSC, Flaherty said other areas being studied (but lacking broad advisory panel support) include traumatic brain injury, acute stroke and traumatic spinal cord injury, among others.

“Like all therapies, further studies will clarify the potential that these systems will have to offer beyond what has been definitively proven to date,” he said. 

Tags:

Bookmark:

Facebook

Technorati

Newsvine

Google

Related: