Support Surface:
 “A specialized device for pressure redistribution designed for management of tissue loads, micro-climate and/or therapeutic functions (ie any mattress, integrated bed system, mattress replacement, overlay or seat cushion).”
National Pressure Ulcer
Advisory Panel (NPUAP).

download a PDF version

return to education

The market for speciality support surfaces is broadening into homes due to a shift from expensive hospital stays to alternate and ‘at home’ care. As such, consumers are seeking better information about the available products, and help in understanding which product is right for them.

This article looks at how therapeutic support surfaces work and reviews the different types of support surfaces on the market, with a focus on features, uses, benefits and disadvantages.

Support surfaces are the special mattresses, mattress overlays, seat cushions and specialty beds that support your body in bed or in a chair. Specifically, these support surfaces are used to reduce or relieve pressure that the weight of your body, and especially your bones, exert on your skin as it presses against the surface of a bed or seat of a chair.

The word ‘pressure’ describes a force over an area – in this case, the pressure of a mattress or seat cushion against a patient’s skin. A pressure reducing support surface lowers pressure below that exerted by a standard mattress – relieving pressure below the capillary closing pressure of 26-32 millimetres of mercury (mmHg). Note that pressure of 70 mmHg applied to healthy tissue for just two hours can result in tissue damage.

By relieving or reducing this pressure, therapeutic support surfaces are designed to prevent or promote the healing of pressure ulcers by reducing or eliminating tissue interface pressure, minimising surface friction to reduce shear, and providing temperature and moisture control.

A number of different types of support surfaces are available and no single support surface has been shown to consistently perform better than all others under all circumstances. The type of support surface best for you will depend on a number of factors such as your general health, your ability to change positions, and your body build, as well as the condition, number and location of your pressure ulcer/s.

Your health care provider will make the appropriate choice during any hospital stay and can recommend support surfaces for use at home. Additional support surface selection considerations for the home include the ease of use of the support surface, maintenance requirements, personal preferences, insurance coverage and availability.

The look of the product is also important in the home environment. When someone walks into your room, one of the first things they see is the bed and mattress, equipment that doesn’t look clinical is a real benefit to maintaining your sense of home.

Of course cost is another important factor. When selecting therapeutic support surfaces, it is critical to evaluate their clinical efficacy and application in proportion to their acquisition cost. Costs for therapeutic support surfaces vary widely, ranging from hundreds of dollars to tens of thousands – and with no compelling evidence to show that one support surface works better under all circumstances, it is important to evaluate the product that is right for you.

Anyone using a pressure reducing support surface should have a care plan, established in consultation with your physician and home care nurse, which should generally include the following:

1. education of the patient and caregiver on the prevention and/or management of pressure ulcers
2. regular assessment by a nurse, physician, or other licensed healthcare practitioner
3. appropriate turning and positioning
4. appropriate wound care (for stage 2, 3, or 4 ulcer)
5. appropriate management of moisture/incontinence
6. nutritional assessment and intervention consistent
   with the overall plan

guidelines for use

The AHRQ is the Agency for Healthcare Research and Quality – the USA’s lead Federal agency for research on health care quality, costs, outcomes, and patient safety (formerly known as the Agency for Health Care Policy and Research).

Guidelines developed by the AHRQ for managing existing pressure ulcers include the following:

• Use positioning devices to raise a pressure ulcer off the support surface. If the patient is no longer at risk for developing pressure ulcers, these devices may reduce the need for pressure-reducing overlays, mattresses, and beds. Avoid using donut-type devices.
• Assess all patients with existing pressure ulcers to determine their risk for developing additional pressure ulcers. If the patient remains at risk, use a pressure-reducing surface.
• If patients can assume a variety of positions without bearing weight on the lesion and without “bottoming out,” a static support surface should be used.
• If the patient cannot assume a variety of positions without bearing weight on the ulcer, if the patient fully compresses the static support surface, or if the pressure ulcer does not show evidence of healing, a dynamic surface should be used.
• If the patient has large stage III or stage IV pressure ulcers on multiple turning surfaces, a pressure relieving product is warranted.

The performance characteristics suggested by the AHCPR for decisions on support surfaces include providing an increased support area, low moisture retention, reduced heat accumulation, shear reduction and pressure reduction properties. Other properties for consideration are the dynamic versus static properties and cost
per day.

categories of support surfaces

Before discussing specific types of support surface devices, it is helpful to have a general understanding of the categories of support surfaces. Support surfaces can be categorised according to whether the support is “dynamic” or “static.”

Static devices reduce pressure by spreading the weight of the body over a larger area. Static devices mould to the contours of the body and maintain a constant level of inflation.

Dynamic devices usually use electricity or battery pack to alter the level of support (through inflation and deflation of air or movement of fluid) provided in the different chambers within the support device. The intent of this type of product is to constantly change the pressure of the support surface against the skin, particularly at the body’s pressure points.

Support surface technologies can be classified in many different ways but usually according to their mechanical characteristics or unique therapeutic function. In practice, most products consist of a combination of materials and incorporate multiple therapeutic strategies.

elastic foam

Foam support surface products are made from two basic types of foam – open cell (a permeable structure with no barrier between cells that allows liquid and gas to pass through) or closed cell (a non-permeable structure with barrier between cells that prevents gas or liquid to pass through).

An ideal combination of characteristics for an elastic support surface would be resistance that also adjusts to pressure. The support surface should have a resistance to pressure that is high enough to fully support the load (prevent bottoming out) without providing a reactive force (memory) that is too high to keep interface pressure low.
Foam is said to have “memory” because of its tendency to return to its nominal shape or thickness. However over time and with extended use, foam degrades and loses its stiffness. This results in higher interface pressures. Foam mattresses typically wear out in three years, and start to bottom out.

Foam tends to increase skin temperature because foam materials and the air they entrap are generally poor conductors of heat.

viscoelastic foam

Viscoelastic foam products consist of viscoelastic, 100% open cell foam that is temperature sensitive. The foam becomes softer at operating temperatures near body temperature, improving pressure distribution at the layer of foam nearest the body.

Viscoelastic foam acts like a self-contouring surface because the elastic response diminishes over time, even after the foam is compressed. The disadvantage of the temperature and time-sensitive response is that the desirable effects may not be realised when the ambient temperature is too low.

fluid-filled

Fluid-filled products may consist of small or large chambers filled with air, water or other viscous fluid materials such as silicon elastomer, silicon, or polyvinyl. The fluid-flow from chamber to chamber or within a single chamber is passive in response to movement and requires no supplemental power.

The term ‘air flotation’ is sometimes used to describe interconnected multi-chamber surfaces. For air cushions, care must be taken to maintain the correct level of inflation to achieve optimal pressure reduction. Under-inflation causes bottoming out and over-inflation increases the interface pressure. Most fluid-filled products permit a high degree of immersion, allowing the body to sink into the surface as the surface conforms to bony prominences. This effectively increases the surface pressure distribution area and lowers the interface pressure by transferring the pressure to adjacent areas.
Skin temperature is affected by the specific heat of the fluid material contained in the support surface. Air has a low specific heat (limited ability to conduct heat) and water has a high specific heat (greater capacity to increase heat flux).

air-fluidised

Air-fluidised beds have been available since the late 1960s and were originally developed for use with burn patients. These products consist of approximately 2,000 pounds of silicon (glass) beads encased in a polyester or Gore-Tex sheet. The beads take on the characteristics of a fluid when warm pressurised air is forced up through them.

Air-fluidised beds use fluid technology to decrease pressure through the principle of immersion while simultaneously reducing shear. These products permit the highest degree of immersion currently available, allowing the surface to conform to bony prominences.

The pressurised air in these products is generally warmed to a temperature of 28 to 35 degrees Celsius. This warming feature can be beneficial or harmful, depending on specific patient characteristics. For example, heat may be harmful to patients with multiple sclerosis or beneficial for patients in pain. In any case, the beneficial effects must be balanced against the increasing metabolic demands of tissue.

low-air-loss

Low-air-loss systems use a series of connected, air-filled cushions or compartments. These are inflated to specific pressures to provide loading resistance based on the patient’s height, weight and weight distribution. A pump circulates a continuous flow of warmed air through the device, replacing any air that is lost through the surface’s pores.

In low-air-loss systems, the patient lies on a loose-fitting, waterproof cover that is placed over the cushions. The waterproof covers are designed to envelop and decrease friction, allowing air to pass through the pores of the fabric – they are usually made of a special nylon or polytetrafluorethylene fabric with high moisture vapour permeability.

In addition, the circulating air is warmed, however, the constant air circulation and evaporation tend to keep the skin from overheating.

In low-air-loss systems, the patient’s skin is in contact with the cover. The local tissue environment is a function of the moisture permeability, the airflow and porosity and the thermal insulation of the cover.

alternating (dynamic) pressure

Alternating or dynamic pressure systems consist of adjacent air chambers or cylinders that are alternatively inflated and deflated by a pump, producing alternating high and low pressures between the patient and mattress and thus diminishing the time any one area is exposed to high pressure.

Alternating pressure appears to have a dramatic effect on increasing lymphatic flow, and providing true pressure relief by consistently reducing the interface pressure below the capillary closing pressure.

The concept of alternating pressure for prevention of tissue ischemia is not new. Kosiak concluded in 1961, “since it is impossible to completely eliminate all pressure for a long period of time, it becomes imperative that the pressure be completely eliminated at frequent intervals in order to allow circulation to the ischemic tissue.”

Rather than increasing the surface area for distribution through immersion and envelopment, alternating pressure devices distribute the pressure by shifting the body weight to a different surface contact area. This may increase the interface pressure of that area during the inflation phase.

Alternating pressure technology has the same potential as any other fluid filled support surface to influence temperature at the interface and care must be taken to maintain the correct levels of inflation based on patient specifications. The skin moisture control and temperature control characteristics of an alternating pressure surface also depend on the characteristics of the cover and supporting material