Wounds and Warmth

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April 2002

By C.A. Wolski

A study looks at the efficacy of warming therapy in treating pressure ulcers.

Since the earliest days of civilization, healers have known intuitively that there is a correlation between the application of warmth and the healing of wounds. "So-called warming therapy...has been in [use] since Greek and Roman times," says Luther C. Kloth, MS, PT, CWS, FAPTA, professor of physical therapy at Marquette University, Milwaukee. "People have used warmth from some source, it may have been warm water, warm applications of mud, or sunshine.

"In the 1960s and '70s, nurses, physical therapists, and physicians were ordering infrared heat lamps to treat wounds. The idea was to actually dry out the wound...and close it. That had a detrimental effect on wound healing, because even though the wound closed, it never really healed....Physical therapists have been using various forms of therapeutic heat to treat musculoskeletal conditions since the early 1900s. They used different types of heating modalities, like heat packs, warm whirlpools, diathermy, and ultrasound. However, until recently there has not been a warming therapy device intended specifically for chronic wounds," Kloth explains.

Does Warming Therapy Work?
However, Kloth and his colleagues from Marquette and Milwaukee's Zablocki Veterans Affairs Medical Center recently completed a randomized clinical trial using a warming therapy device and have shown that warming therapy is an effective way to treat pressure ulcers.

The study used a device that consisted of a 2-cm-thick foam wound cover with a plastic window in the center that allows the insertion of a credit card-sized infrared heating element. The element was not in contact with the wound and was attached to a battery-operated control unit. "[Warming therapy] delivers a controlled level of infrared heat into the wound and to the intact surrounding skin," says Kloth. "The amount of intact surrounding skin is controlled by the size of the wound cover. You have small wounds, intermediate size-wounds, and large wounds. A wound cover is selected that allows 1 to 2 cm of skin to be visualized through the window of the cover, because you want that heat to actually warm up the surrounding skin, as well as the interior of the wound."

The 12-week study, which was initiated at Marquette University and enrolled patients from the Zablocki VA Medical Center and seven nursing homes, was a follow-up to an earlier, 4-week study. In the most recent study, there were 40 patients with 43 wounds; 21 wounds underwent the warming therapy 24 hours a day, 7 days a week for 12 weeks, and 22 received standard care only. In the earlier study, patients in the experimental group received both standard wound care and warming therapy for 4.5 hours a day, 5 days a week.

Patients had to meet a number of criteria before they could be included in the study. Participants could not be smokers, have uncontrolled diabetes, have a terminal illness, or be undergoing any other wound treatment while in the study. "The wound had to be clean and free of necrotic tissue," says Sonia Dumit-Minkel, MD, PT, a senior physical therapist at Zablocki VA Medical Center, adding that the wound also had to be more than 2 weeks old. The participants ranged in age from 42 to 101 years old with a mean age of 75.7 years. All of the patients were inpatients either in nursing homes or in the VA spinal cord unit.

The warming therapy was delivered at 38°C (100.4°F), slightly above body temperature, for a specific reason. "Normothermia means 37 plus or minus 1° Celsius-the core temperature of the body is 37°C, but the interior of wounds is often cooler," says Kloth. "They can be as cool as 33°or 34°C. Studies have shown that when the wound fluid is cool, say 33°or 34°C, [it] seems to have an inhibitory effect on healing, and there are certain enzymes in that cool wound fluid that are perhaps causing the inhibitory effect. Recent research suggests that warming the wound and wound fluid weakens the inhibitory effect. The warmer wound environment may make it possible for cells involved in the tissue repair processes, like the fibroblasts, to increase in number, and since fibroblasts are responsible for generating collagen for repair processes, they can do their intended production of collagen in a warmer environment."

Results
The results of the study show that warming therapy may deliver a higher, faster degree of healing than standard care. After 12 weeks, pressure ulcers treated with warming therapy healed at a rate more than 50% faster than the control wound treated with standard care. Using regression analysis, Kloth and his team found that achieving a 100% closure rate would take 78 days with the warming therapy and 180 days with standard care alone. In the original, shorter study, the experimental group had a 61% closure rate; the control group had a 19% closure rate.

Although the team chose patients who had no factors affecting their ability to be healed, there were no factors predicting whether a patient would be successfully healed using the warming therapy, according to both Kloth and Dumit-Minkel. "There are so many variables in human beings," says Kloth. "When you do a clinical research study, you try to reduce as many of those variables as you can, that's why you have inclusion and exclusion criteria. There are a lot of factors that impede healing in people.... So you have to try to exclude the poor healers. You can't have poor healers on one side of the study and good healers on the other side, then it is biased."

These findings have implications for the future of wound care. "I hope in the future we'll be able to use the [device], because patients do benefit tremendously from [it]," says Dumit-Minkel. "We're going to continue to do studies-hopefully, a larger study with more subjects that will last longer." The Zablocki VA Medical Center is not the only hospital conducting warming therapy studies. For instance, Louisiana State University Medical Center, Shreveport, is studying the use of warming therapy on diabetic foot ulcers, and others are exploring the use of warming therapy in the treatment of venous leg ulcers.

For all its promise, warming therapy will continue to be an adjunct to traditional treatment. "Clinicians who treat patients with chronic wounds, whether they are nurses, physical therapists, or physicians, usually try a few weeks of standard care," says Kloth.

"Standard care is usually some form of debridement, a dressing that keeps the wound tissues moist, and, if it is a pressure ulcer, you have to remove the pressure...standard care will be done as much as 3 weeks or a month. During that period of time, progress is monitored by taking wound measurements. After 3 weeks of treating a pressure ulcer with standard care, the measurements get worse, maybe stay the same, or make significant progress toward closure. If it makes significant progress toward closure, standard care may continue. If it is standing still or regressing, it is time to change the treatment.... Any new treatment, be it for wounds or for something else in medicine, has to undergo a lot of clinical research showing that it does better than the standard of care before it becomes the standard of care."

C.A. Wolski is associate editor of Rehab Management.

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April 2002