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Certain Techniques While Applying Casts May Decrease Incidence of Thermal Injury to Skin
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Posted on: 11/21/2007
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When casts are applied to limbs for immobilization, a reaction occurs between the materials that produces heat - sometimes hot enough to cause damage to the skin below. While cast-related complications, such as burns, are not unusual, there isn't much research available on how these may be prevented.
The authors of this study investigated the reasons for the injuries, despite the availability of new materials that were meant to reduce the risk. To do this, the researchers looked at the variables that can affect the production of heat. These included ambient temperature, temperature of the reactants, and the reactants themselves.
Earlier studies have shown that more layers (over eight), reusing dip water, and warmer dip water all can contribute to producing heat.
Because it would not be ethical to test cast temperatures on patients, the researchers devised a model with which they could measure the amount of heat produced by the casting material and process. They included several variables in the trial, such as the diameter and shape of the limbs, the thickness of the plaster application, the type of cast, the dip water temperature, or if placement of the cast on a pillow while the cast was setting or curing. With the plaster casts, the researchers applied six, 12, and 24 ply over three or four layers of cotton.
The results of the study showed that the external temperature of a plaster cast was on average, 2.7 degrees Celsius (plus or minus 1.9 degrees) cooler than the internal temperature. The researchers found that dip water temperature that was less than 24 degrees as more likely to prevent thermal damage, regardless of how thick the plaster cast was. They also found that the thinner the cast, the less important the dip water temperature as long as it was below 50 degrees.
A thicker plaster cast, of 24 ply, could cause significant burns if the dip water was at 50 degrees. The same finding occurred with 12-ply casts that were folded over on the end - effectively doubling the thickness.
Smaller limbs saw slightly higher temperatures (50.9 degrees, plus or minus 1 degree), while the standard size had a lower temperature of 50.5 degrees (plus or minus 1 degree) and the larger limbs a temperature of 49.9 degrees (plus or minus 1.7 degrees). The shape of the limb caused a difference: an L-shaped limb consistently produced higher temperatures than did the straight limbs (60.1 degrees and 52.1 degrees, respectively). When the researchers eased the curve with a slap of plaster and by reducing the number of wraps in the curve, the temperature dropped significantly.
When the researchers applied fiberglass over plaster, the temperature rose high enough to cause a burn, as did placing a limb with a 12-ply cast on a pillow; with the bottom part of the cast being quite a bit warmer than the top part.
Some interventions to decrease the temperature of the cast include applying ice packs between limb and pillow or avoid using the pillow if possible. The authors do not agree with the practice of applying isopropyl alcohol to the cast to decrease the temperature, as they found it only decreased the outer temperature, not the inner temperature. They commented that this could lead the physician to think the cast is not as hot inside as it may be.
The researchers conclude that cast thickness should not be overly thick, the dip water should be kept below 24 degrees, and that splints should be fit for the limb and not folded over as this will double the thickness. If fiberglass is to be used, it should not be applied until after the plaster has fully cured. Finally, avoiding use of a pillow is preferable.
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References:
Matthew A. Halanski, MD, et al. Thermal Injury with Contemporary Cast-Application Techniques and Methods to Circumvent Morbidity. In The Journal of Bone and Joint Surgery. November 2007. Vol. 89. Pp. 2369-2377.
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