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Putting Strokes on Ice

Cooling patients off could minimize the long-term damage caused by stroke or heart attack.
April 23, 2001

Scientists have long known that a drop in body temperature can minimize damage done to the brain and other cells by oxygen deprivation. Indeed, stories of surprising recoveries after a fall into icy-cold water have tantalized researchers for years.

Harnessing this natural preservative power, a Redwood City, CA-based startup, Radiant Medical, has begun clinical trials of a device that lowers body temperature a few crucial degrees in patients suffering from stroke or heart attack, two common causes of oxygen deprivation.

Animal studies in the last six years have shown that a drop in body temperature can preserve brain tissue after a stroke, reducing by half the stroke’s impact on surrounding tissue. With reduced temperature, cellular metabolism slows down, decreasing the amount of oxygen and other nutrients needed to survive. Lower temperature can also slow or arrest the cascade of events that lead to cell death.

Keeping Cool Inside

Early attempts to induce hypothermia-lower-than-normal body temperature-relied on surface cooling, which was uncomfortable for patients. Shivering actually heats the body, so patients needed to be immobilized and put on a respirator. Often, pneumonia resulted.

Radiant says its new device, called SetPoint, reliably cools the body’s blood supply without chilling the patient. Wrapped in a warming blanket and given a mild tranquilizer, the patient generally feels warm throughout the procedure.

The SetPoint device joins a heat-exchange catheter and cassette with a control unit that regulates the temperature of the sterile saline solution circulating through the cassette and catheter.

The catheter is inserted in the thigh into the femoral vein and guided through the network of blood vessels until it reaches a vein near the heart. “The blood is cooled as it passes over the catheter,” says Mike Dineen, Radiant’s director of marketing. “The cooled blood circulates through the body and enters the head, cooling brain tissue.”

For stroke patients, SetPoint is used to induce moderate hypothermia: body temperature is cooled to 33 °C (91.4 °F) for 24 hours, then slowly rewarmed to 37 °C (98.6 °F). The device allows clinicians to precisely control the target temperature as well as the rate of cooling and warming.

Just in Time

The stroke treatment is currently being tested at the Cleveland Clinic Foundation, among other sites. “Hypothermia tightens the vessels and reduces inflammation,” says Michael DeGeorgia, head of neurological intensive care at Cleveland Clinic.

“We hope that keeping patients cold will reduce stroke volume, giving us more time to figure out the source of the stroke,” he says. “It also reduces the risk of hemorrhage when clot-busting drugs are administered, so there is reason to believe that using hypothermia together with the drugs will improve patients’ functional outcome.”

Tests of SetPoint in the treatment of heart attack patients are also underway at William Beaumont Hospital in Royal Oak, MI, and St. Vincent’s Hospital in Melbourne, Australia.

In cases of stroke, the aim is to apply SetPoint within 12 hours, and for heart attack, within the first six hours after oxygen deprivation occurs. Most physicians agree that to prevent further damage, the device must be used relatively soon after the event occurs.

If trial results are positive, the next step will be to deliver SetPoint within a narrower window of time-perhaps when heart attack or stroke is only suspected. According to DeGeorgia, it would be ideal if “a technician [would] start the hypothermia process on the way to the hospital or in the emergency room.”

Besides minimizing the long-term damage caused by stroke or heart attack, SetPoint’s usefulness for patient temperature management will be tested in additional areas-general surgery and postoperative care-in the near future.

Two other California companies-Innercool Therapies in San Diego and Alsius in Irvine-are developing similar cooling devices for use in fever control and aneurysm surgeries.

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