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Take the load off by choosing the right support surface

Maklebust, JoAnn RN, AOCN, APRN, BC, MSN


Bewildered by the plethora of choices in pressure-reducing surfaces? Find out how they work so you can choose wisely and appropriately.

A wound care expert tells you about pressure-reducing surfaces and how they can help protect your patient's skin from breakdown.

ACCORDING TO THE National Pressure Ulcer Advisory Panel, most pressure ulcers are treatable and most are preventable–yet patients still die of pressure-ulcer-related complications. One way you can make a difference in your patient's care is by learning how support surfaces, such as mattress overlays, mattress replacements, and specialized beds, relieve or redistribute pressure on skin and prevent pressure ulcers from forming or worsening. To understand why support surfaces help, first consider the pathophysiology of pressure ulcer formation.

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Damaging duo: Pressure and shear

Two forces can damage soft tissue: pressure and shear.

  • Pressure ulcers are caused by compression of soft tissue between bony prominences and an external surface, such as a chair or bed. When external pressure exceeds capillary blood pressure, blood flow is impeded, causing tissue ischemia and breakdown. Because muscle is more sensitive to pressure than skin, underlying tissue may be necrotic by the time you see a lesion on the skin surface.
  • Shearing forces reduce the ability of tissue to withstand pressure: Tissue subjected to shear force can suffer ischemia at only half the pressure that would cause ischemia without shear.

Shear can occur when the head of the bed is raised more than 30 degrees. Positioned at a steeper angle, the patient tends to slide downward. Her skin sticks to the bedclothes or sheets, pulling away from underlying tissue and becoming distorted. In the process, capillaries stretch and tear, reducing local blood flow. The result may be a shear ulcer with wide areas of undermining between the skin and deeper tissue. Shear combined with pressure may be responsible for the high incidence of sacral pressure ulcers.

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Reducing pressure

Three major components contribute to pressure ulcer development: pressure duration and pressure intensity, for which you can intervene, and tissue tolerance (more on this later).

Repositioning the patient's body reduces the duration of pressure and using support surfaces reduces the intensity of pressure. Use these interventions to take the load off body pressure points.

To reduce pressure and sacral shear, elevate the head of the patient's bed no higher than 30 degrees. If she can't lie flat because of cardiopulmonary conditions or enteral tube feedings, keep the head of the bed at the lowest possible angle. When you reposition her side to side, support her in a 30-degree lateral position rather than on her trochanter at a 90-degree angle. Using a 30-degree side-lying position avoids putting pressure on the sacrum and the trochanter simultaneously.

Use pillows or foam wedges to separate bony prominences, such as knees and ankles, and place pillows under the patient's lower legs to lift her heels off the bed.

Neither time nor pressure alone causes tissue ischemia. We've been taught to reposition patients at least every 2 hours because of the inverse relationship between pressure and time: A person can endure a great amount of pressure for a short amount of time without sustaining tissue damage; a ballet dancer standing on her toes is a good example. Long periods of low pressure cause more tissue damage than short periods of high pressure. Also, repeated pressure insults to the same area before it has a chance to recover may cause cumulative tissue damage, which can lead to a pressure ulcer.

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Tackling tissue tolerance

Every patient has a different tissue tolerance, or the amount of time she can tolerate the effects of pressure. You'll need to determine how long your patient can tolerate pressure against the skin. An elderly patient with fragile skin or little soft tissue may not be able to tolerate one position for even 2 hours without damage. Use a pressure ulcer risk assessment tool to determine your patient's risk. If she's at risk for skin breakdown, check her skin over bony prominences for signs of pressure intolerance: nonblanchable erythema, pain, edema, heat, or changes in skin color compared with baseline. You might also notice persistent redness once pressure has been relieved or blue or purple skin tones in a patient with darker skin. Perform these checks every 24 hours; more often if redness persists with pressure relief.

If your patient is pressure-intolerant, increase her turning frequency and put her on a support surface designed to reduce the intensity of pressure between bony prominences and the bed. No one product works best for all patients in all circumstances. By understanding the properties and performance characteristics of various support surfaces, you can match one with your patient's clinical condition.

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How support surfaces work

To be effective, support surfaces must mold to the body to maximize contact, then redistribute the patient's weight as uniformly as possible. They're designed to work on the principle of Pascal's law: The weight of a body floating on a fluid system is evenly distributed over the entire surface. As pressure is increasingly distributed over more body surface area, the intensity of pressure decreases over all body areas. Support surfaces also use the principle of deformation: They must be capable of deforming enough to permit prominent areas of the body to sink into the support. Finally, they must be able to transmit pressure forces from one body area to another.



The degree of head elevation can affect the clinical effectiveness of a support surface. When the head of the bed is elevated, pressure is shifted to the sacral and ischial areas of the body. The patient may “bottom out” if the seating area of the support surfaces flattens and loses volume. If bottoming out occurs, the support surface no longer provides therapeutic benefit.

To determine if bottoming out has occurred, place your hand, palm up and fingers outstretched, between the mattress overlay and the hospital mattress. The support surface should have about 1 inch (2.5 cm) of uncompressed support surface between your hand and the patient's body. If you can feel the patient's body lying on your hand, the mattress needs more depth. Add more air to the mattress or provide a thicker support surface so the patient doesn't bottom out.

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Getting specific

Mattress overlays and mattress replacements can provide pressure relief with foam, air, gel, or water, alone or in combination. All of these mattresses or overlays deteriorate over time. The Centers for Medicare and Medicaid Services divides support surfaces into three groups:

  • Group 1 surfaces don't require electricity and include air, foam, gel, and water mattresses or overlays. These surfaces are intended for pressure ulcer prevention.
  • Foam surfaces come in various densities (or weights), depths, and construction. To reduce pressure, foam must be high quality and at least 4 inches (10 cm) thick.
  • Static air overlays have multiple chambers that allow air exchange between compartments (or cells) when a person lies on the surface. The air exchange between cells allows the surface to deform and permits the body to sink into the surface, reducing pressure on bony prominences. Maintain adequate air volume with inflation or reinflation devices.
  • Gel mattress overlays have a tissuelike composition that reduces shear and supports weight without bottoming out. They're self-sealing if punctured and can be reused. Gel doesn't deform easily and may become stiff over time.
  • Group 2 surfaces include dynamic powered surfaces and advanced nonpowered surfaces. These surfaces are indicated for patients with Stage III or Stage IV pressure ulcers on the trunk or pelvis, muscle flap repair of a pressure ulcer within the last 60 days, or multiple Stage II pressure ulcers that haven't improved on a Group 1 surface in the last month, even with comprehensive care (more on that later).
  • Dynamic air overlays are used with a mechanical pump to alternate inflation and deflation of chambers and constantly change pressure points. Air chambers must have enough depth and be close enough together to lift the body during alternating cycles.
  • Low-air-loss systems are available as mattress overlays and whole bed systems. An air compressor inflates the mattress cushions. It also circulates air across the patient's skin to reduce moisture.
  • Group 3 consists of air-fluidized beds, a high-air-loss system with ceramic silicone beads that become fluidized as warm pressurized air is forced up through the beads. This gives the beads the characteristics of fluid, allowing the patient's body to float on the surface and minimizing pressure, shear, and moisture. A Group 3 surface is indicated for patients with Stage III or Stage IV pressure ulcers that haven't improved on a Group 2 surface over the last month, even with comprehensive care.

See Characteristics to Consider When Choosing a Support Surface for more tips on evaluating support surfaces for patient use.

Support surfaces are no substitute for careful nursing care and educating the patient and family about wound care. Comprehensive care includes a nutrition plan to optimize wound healing, managing incontinence or moisture, good local wound care (including treating wound infection), repositioning your patient every 2 hours, and assessing her skin and pressure points for potential problems each time you turn her. If you find persistent pressure areas indicating tissue intolerance, consult a wound specialist for alternative pressure-reducing devices. He may recommend a different type of support surface to take the load off.

With proper care, your patient's pressure ulcer should show signs of healing in 2 to 4 weeks. If you don't see signs of improvement, reassess your interventions for pressure reduction, adequate nutrition, and good local wound care. All three areas are key to healing your patient. ▪

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Characteristics to consider when choosing a support surface

  • Pressure redistribution. The surface should support the patient's body weight without harming her skin.
  • Skin moisture control. The surface should keep her skin dry.
  • Skin temperature control. The surface shouldn't make her sweat.
  • Friction. The surface should let her transfer but not slide off.
  • Infection control. The surface shouldn't promote bacterial growth.
  • Flammability. The surface shouldn't ignite if someone drops a lighted cigarette on it.
  • Product service requirements. The owner's manual should describe how to clean and maintain the surface.
  • Life expectancy. The manual should indicate how long the surface is expected to last, so it can be replaced before problems arise.
  • Fail safety. The manual should tell you what to do if the surface becomes unusable.

JoAnn Maklebust is a wound care clinical nurse specialist and a nurse practitioner in the department of surgery at Barbara Ann Karmanos Cancer Institute at Detroit Medical Center and associate clinical professor of nursing at Wayne State University, both in Detroit, Mich.

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Brienza, D., et al.: “Seating, Positioning, and Support Surfaces,” in Wound Care Essentials: Practice Principles, S. Baranoski and E. Ayello (eds). Philadelphia, Pa., Lippincott Williams & Wilkins, 2004.
    Cuddigan, J., and Ayello, E.: “Treating Severe Pressure Ulcers in the Home Setting: Faster Healing and Lower Cost with Air-Fluidized Therapy,” The Remington Report. 12(3):6–10, May/June 2004.
      Cullum, N., et al.: “Beds, Mattresses, and Cushions for Pressure Sore Prevention and Treatment (Cochrane Review),” Chichester, United Kingdom, The Cochrane Library, John Wiley and Sons, Issue 2, 2004.
        National Pressure Ulcer Advisory Panel: Pressure Ulcers in America: Prevalence, Incidence and Implications for the Future. Reston, Va., National Pressure Ulcer Advisory Panel, 2001.
          © 2004 Lippincott Williams & Wilkins, Inc.