Device placed in vein chills the blood
SAN ANTONIO — Cool runnings, indeed. A tiny device placed inside a central vein can safely refrigerate blood as it flows through stroke patients, lowering their temperature and raising the possibility that they might gain brain protection from hypothermia without having to be packed in ice.
Although the trial didn’t find that stroke patients getting their blood cooled fared any better or worse than a comparison group of patients who weren’t cooled, the technology proved safe enough to clear the way for testing the device in a much larger group, said Thomas Hemmen, a neurologist at the University of California, San Diego Medical Center who presented the data February 25 at the International Stroke Conference.
The new results also demonstrate that stroke patients can be cooled down to 91.4 degrees Fahrenheit safely while they are receiving a powerful clot-busting drug called tPA, the standard treatment given to patients during the first few hours of a clot-induced stroke.
“Cool temperatures have been associated with better outcomes,” said Daniel Lackland, an epidemiologist at the Medical University of South Carolina in Charleston. “We’re seeing some excitement about an intervention with this device.” If further trials support use of this kind of cooling therapy, he said, “that would be a great finding — it’s a relatively easy thing to do.”
Induced hypothermia is mainly used for cardiac arrest patients who have had their hearts restarted but are comatose and risk delivering a shortage of blood to the brain. Because they are unconscious, those patients can be packed in ice.
But stroke patients are awake during treatment, which makes being packed in ice extremely uncomfortable. In the new study, Hemmen and his colleagues teamed with a company called InnerCool Therapies to test a device only a half-centimeter in diameter that causes less discomfort by chilling the blood as it flows through the vena cava, a huge vein that carries blood into the heart from the upper part of the body.
The study included 58 stroke patients who were an average of 66 years old and had been referred to university hospitals around the United States. All of the patients received tPA and 28 of them were also randomly chosen to get blood cooling. At a checkup 90 days later, seven controls and five of the hypothermia group were judged as having little or no disability — not a substantial difference.
Hemmen said this recovery rate for both groups is worse than the average seen in stroke patients nationwide, because many of the patients referred to this study by physicians had severe strokes and previous medical problems. Patients undergoing cooling were more likely to develop pneumonia during recovery, but this didn’t affect their status on average when assessed 90 days after treatment.
Regulators overseeing the study required a one-hour delay from the point at which tPA was given before cooling could be started, which might have limited the benefits of the treatment, Hemmen said.
These preliminary results might rejuvenate the idea of cooling stroke patients. “I kind of thought that hypothermia for stroke had actually gone by the wayside. I’m really pleased it’s come back,” said neurologist Cheryl Bushnell of Wake Forest University Health Sciences in Winston-Salem, N.C. “Overcoming the technological issues of cooling is a major benefit.”
The protective effects of cooling are well documented in incidents of drowned people being revived with little brain damage after falling though the ice on frozen lakes. But the precise biological mechanism responsible for this benefit is poorly understood. Slowing metabolism may limit cell death, Bushnell said.
Hemmen said a randomized trial of 400 first-time stroke patients is being planned that will start cooling and administration of tPA simultaneously.
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