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December 2003


Under the Surface

By Thomas A. Krouskop, PhD, and Janet Davis, MSN, RN, APRN-BC, CWOCN
Caregivers can play a large role in selecting support surfaces to prevent wounds.

Support surfaces are an essential part of a comprehensive pressure management program. However, they are only some of the many tools required to render the holistic care needed to prevent or treat pressure ulcers. They do not prevent wounds nor do they heal wounds—people providing patient care prevent and heal wounds. The support surface, the metabolic status of the person, and the psychological stress on the person combine to determine the frequency and intensity of the care that is required to prevent or heal a wound. Support surfaces cannot replace fundamental medical care because they cannot correct underlying pathophysiologic conditions.

Fundamental care practices must continue regardless of what support surface is used. Some examples of these fundamental care practices are turning, repositioning, and mobilizing patients in and out of bed/chairs; assisting patients with feeding; skin checks with basic skin care; and skin care related to incontinence. If a patient has an existing pressure ulcer, then care of the ulcer and managing bacterial load are additional care responsibilities.

Prior to the late 1970s, pressure ulcers were thought to be the result of an ischemic event as explained by early researchers in the field.1,2 The ischemic event model formed the basis for using 32 mm Hg as a threshold for acceptable pressure and unacceptable pressure. However, the ischemic model for pressure ulcers has not explained the inverse relationship that exists between the magnitude of the applied pressure and the time required to create a wound. It also does not explain why increasing the pressure above that required to stop blood flow decreases the time it takes to create a wound. Moreover, the tissue oxygenation model is difficult to use to explain how nutrition, metabolic disorders like diabetes, and psychological stress affect risk for developing a pressure ulcer.

During the late 1970s a new model was developed.3 Based on this model, a support surface should be expected to contribute to controlling four conditions:
  • pressure gradients in the tissue,
  • comfort and reduced anxiety,
  • moisture at the skin interface, and
  • temperature at the skin surface
By helping to control these variables, a support surface contributes to the environment where care can be provided. With the proper use of an appropriate support surface, a more conducive wound environment can exist and healing promoted once the mechanical loads are reduced at the wound site. Once pressure and shear are relieved in the area of the wound site, the cellular activities of wound healing can take place more effectively.

Choosing a support surface

After a comprehensive evaluation of the patient, decisions regarding care need to be made. Which support surface is most appropriate or if a support surface is needed are frequently faced questions. Many facilities have support surface algorithms, decision trees, or protocols. These algorithms are tools to assist the caregiver in providing the most appropriate surface for that patient’s individualized need. In a perfect world, the facility would have access to any or all surfaces. However, most facilities have only one company-sponsored support surface line from which to choose.

The selection algorithms may be risk factor-based, ulcer characteristic-driven, or a combination of both. In the risk factor-driven selection protocol, a support surface may be recommended if the patient exhibits certain risks or scores within a predetermined range from a risk assessment tool, like the Braden Scale. In the ulcer-driven protocol, the patient with a particular stage of ulcer on a particular body location may guide the caregiver toward a particular type of support surface. Whatever algorithm is used, the caregiver is directed to a decision for providing consistent care in managing the mechanical loads acting on the tissue. The AHCPR Clinical Practice Guideline for Treatment of Pressure Ulcers #15 has a decision tree-style algorithm for choosing a support surface.4 This algorithm provides the best evidence available in the use of support surfaces.

Commercially available products can be grouped based on what is used to construct them, and knowing the characteristics of the group may help when selecting a product. Some of the primary advantages and disadvantages of each support product group are given below.

Air-filled products: advantages are they are lightweight and easy to clean, and reduce pressure gradients; temperature can be controlled at the skin interface; and the multiple compartmental versions allow positioning. Disadvantages include that they are subject to puncture and have problems with user stability, and inflation must be checked frequently. Liquid-filled flotation devices: advantages are they are cleanable and reduce pressure gradients, and the temperature at the skin interface can be controlled. Disadvantages are they are subject to puncture and are heavy, and it can be difficult to position the user. Gel-filled devices: advantages are they adjust to body movement and are cleanable. Disadvantages include their weight, cost, and need for appropriate storage space. Foam products: advantages are their availability, many variations, relatively low cost, and light weight; they can be used to position the user, and can be modified to control pressure gradients. Disadvantages are their lack of durability, they are not easily cleanable, their properties change with time, and they may support combustion. When foam products are used, it is suggested that three parameters be used when ordering the products. The first parameter is the thickness of the foam. The second measure is the ILD or IFD. The ILD is a measure of stiffness, and it is the force (in pounds) required to press an 8" diameter circular platen into a 16" x 16" slab of foam a certain percentage of the slab thickness. A 25% ILD is the force required to compress a 4" piece of foam down until it is 3" tall under the platen. The third measure, density, is a measure of the amount of material in the foam, and it is generally measured in pounds per cubic foot. Typical values for mattress overlays are: a thickness of 3-4", 25% ILD and 30 pounds, and a density of 1.3 pounds/cubic foot. In some cases, a simple mattress overlay or a replacement mattress may not be the most effective tool for protecting and nursing an individual. In situations where a patient has a high risk of developing a pressure ulcer as indicated by one of the assessment algorithms, has limited access to nursing care, and/or has complications that prohibit the user from being repositioned, an air flotation bed should be considered.

There are two basic categories of air flotation beds. First is the air fluidized bed, which has the following advantages and disadvantages: control of pressure gradients, ease of operation, fail safety, and control of skin maceration. One disadvantage is its heavy weight. The second category is the low air loss bed. The advantages of this class of products include: control of pressure gradients, fail safety, comfort, control of skin maceration, and positioning for posture control. A disadvantage is that they require skilled setup. It should be noted that testing done in our laboratory has shown that air flotation beds, when properly adjusted, produce equivalent interface pressure profiles.

There are a number of other product performance parameters that should be assessed when selecting a line of support surfaces for your facility or patient. These parameters include: life expectancy of product, maximum pressure gradients, effects of user position on support surface performance, weight limits for users, and effects of nursing aids on the pressure profiles, eg, effect of incontinence pads.

Conclusions

In summary, there is no evidence currently available that support surfaces prevent or heal pressure ulcers. Support surfaces are tools that should be used as part of a pressure management program to prevent many wounds from forming and provide an environment in which many wounds can be treated effectively.

Assure that your facility has a written policy for when different support surfaces are to be used and be sure to document patient assessments, patient equipment, skin care and skin assessments, as well as when patients are turned, food intake, blood work, and how plans are being modified in response to the patient’s status. Make sure that you do not undermine the support characteristics of the surface by adding layers of padding and diapers and stiff waterproof covers. These items can mask the performance of the underlying support surface.

Select a company with a representative who works well with your team. Modern air flotation systems provide equivalent pressure relief if they are set up properly and maintained. Set in place a mechanism to monitor the performance of mattresses so they can be replaced in a timely manner and watch for patients who have spent long hours in the operating room, as they will often develop wounds in the ICU. Make sure that they are placed on a support surface that provides low interface pressure distributions and that the skin condition is documented as often as medically possible, especially during the first 5 days. There is evidence that it takes up to 96 hours for pressure-induced damage to become clinically evident, and these wounds often continue to worsen over a period of days regardless of what treatment is started because the damage is already there. A comprehensive pressure management program exists only when fundamental aspects of care along with technological advances are provided. As caregivers, we must remember that we make the difference when we use technology to enhance our care. Technology is not a substitute for care.5 As health care providers, we have critical thinking ability that enables us to provide the most technologically advanced, quality, evidence-based care. Let’s use it to our patients’ benefit.

Thomas A. Krouskop, PhD, is a professor of physical medicine and rehabilitation at Baylor University, Houston, and Janet Davis, MSN, RN, APRN-BC, CWOCN, is a nurse with the University of Texas MD Anderson Cancer Center in Houston.

References
  1. Kosiak M. Etiology and pathophysiology of decubitus ulcers. Arch Phys Med Rehabil. 1959;40:62-69.
  2. Dinsdale S. Mechanical factors in the pathogenesis of ischemic skin ulcers in swine [PhD thesis]. University of Minnesota; 1974.
  3. Krouskop TA. Synthesis of the factors that contribute to pressure sore formation. Medical Hypotheses. 1983;11:255-268.
  4. AHCPR Guidelines, Treatment of Pressure Ulcers: Clinical Practice Guideline #15. Washington, DC: US Department of Health and Human Services, Agency for Health Care Policy and Research; Washington, 1993.
  5. Garber SL, Reddy NP, McLane KM, Krouskop TA. The role of technology in pressure ulcer prevention. In: Krasner D, ed. Chronic Wound Care: A Clinical Source Book for Healthcare Professionals. 3rd ed. Wayne, Pa: HMP Communications; 2001:673-686.

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