Hypothermia devices may improve outcomes.
Dr. DeGeorgia, head of the Neurological Intensive Care Program at the Cleveland Clinic Foundation, noted that the equipment used in the influential studies that found hypothermia therapy reduces mortality was slow to achieve cooling and allowed only imprecise temperature control.
Indeed, he said the air-cooled machine used in one Hypothermia After Cardiac Arrest study group trial (N. Engl. J. Med. 2002;346:549-56) is no longer on the market. Median cooling time was 8 hours, and 70% of patients also required ice packs, Dr. DeGeorgia said.
Another favorable experiment, the Cooling for Acute Ischemic Brain Damage (COOL AID) pilot study (Stroke 2001;32:1847-54), for which Dr. DeGeorgia was an investigator, used a technique he said was developed before he was born. "You could achieve the target temperature, but it was very hard. It took about 4 hours," Dr. DeGeorgia said. The emerging technology falls into two broad categories: surface cooling and endovascular cooling, according to Dr. DeGeorgia. Around longer and akin to a cold bath, surface cooling typically employs blankets filled with ice water, alcohol, or cold air. It is simple and cheap, he said.
Shivering can become a problem, however, as skin receptors respond to the cold by setting off muscle tensing to produce heat. As a result, he said anesthesia or a neuromuscular blockade must be used.
Among the disadvantages of surface cooling, he also listed slow cooling, imprecise controls, thermal injury, and use of nursing time.
Promising cold-water surface cooling systems described by Dr. DeGeorgia include:
* Blanketrol II (Cincinnati SubZero Products, Cincinnati) pumps 2 L/min and has a feedback mechanism, temperature control, and random flow patterns to distribute temperature evenly and effectively.
* Meditherm III / MTA 6900 (Gaymar Industries Inc., Orchard Park, N.Y.) pumps 1 L/min, has a feedback mechanism and temperature control, and encircles the patient's legs and torso for maximum surface coverage.
* Arctic Sun Temperature Management System (Medivance Inc., Louisville, Colo.) pumps 0.5-5 L/ min under negative pressure, so that the blanket does not become distended and is less likely to leak. It also has a biodegradable, highly conductive inner liner reducing contact resistance.
Endovascular cooling with a cold saline solution is fast and easy enough for paramedics to use en route to the emergency room, Dr. DeGeorgia said. "It seems to be pretty safe. I think it has a future," he said, reporting cooling times in minutes instead of hours.
Among the advantages cited by Dr. DeGeorgia are that endovascular cooling offers precise temperature control, does not require general anesthesia or neuromuscular blockade, and demands less attention from nurses. He listed as disadvantages that it is expensive, invasive, and patients may require intubation in response to airway problems that may develop with prolonged cooling.
New devices use counter-current heat exchange, which circulates the coolant in the opposite direction to blood flow to enhance the effectiveness of endovascular cooling. "The blood gets very cold, and the blood returning to the heart is cooled," he said of one device. "It fakes out the cold receptors on the skin into thinking the body is warm. The body was never designed to be warm on the outside and cold inside."
Dr. DeGeorgia described the following new endovascular cooling systems as promising:
* Reprieve Endovascular Temperature Management System (Radiant Medical Inc., Redwood City, Calif.) places a balloon catheter in the vena cava by way of the femoral vein. A microprocessor-driven controller warms or cools normal saline. The triple-lobed, helically wound balloon creates large surface area and promotes optimal heat transfer.
* The Cool Line, Icy, and Fortius Systems (Alsius Corp., Irvine, Calif.). Cool Line has a two-balloon catheter that enters the superior vena cava by way of the subclavian vein. Icy has a three-balloon catheter and Fortius a serpentine balloon catheter, both of which go to the inferior vena cava via the femoral vein.
* Celsius Control System (Innercool Therapies Inc., San Diego) has a thin catheter that also goes through the femoral vein to the inferior vena cava. A metal alloy temperature control element on its tip is more conductive than plastic, and an articulated surface promotes blood mixing.
BY JANE SALODOF MACNEIL
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|Title Annotation:||Cardiovascular Medicine|
|Author:||MacNeil, Jane Salodof|
|Publication:||Internal Medicine News|
|Date:||Apr 1, 2005|
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