How to guide: Selecting a support surface
Pressure Ulcers | Liz Ovens, Clinical Service Lead Tissue Viability, Hillingdon Community Health and Central and North West London Foundation Trust
The use of an appropriate support surface is a key element of the prevention and management of pressure ulcers (NICE, 2005). However, the wide array of support surfaces available and the different technologies used can cause confusion. This ‘how to’ guide aims to help clinicians choose the best support surface for a patient’s individual needs.
What is a support surface?
A support surface takes the weight of the patient when lying or sitting, and is intended to spread out (redistribute) the pressure exerted on the tissues in contact with that surface. The term support surface can apply to specialist beds, mattresses and mattress overlays, and also to chair and wheelchair cushions.
Why is pressure redistribution important?
Pressure is a major contributor to the development of pressure ulcers. If sufficiently high, pressure may reduce blood flow to the tissues, and cause direct damage to cells and tissues. Usually, the reduction in blood flow causes the patient to change position to relieve the pressure and allow blood to flow again. However, if the pressure is not relieved for some reason, eg the patient is unable to move, or has a loss of sensory function, the reduction in blood flow can damage skin and soft tissues. The damage may cause a pressure ulcer.
In addition to pressure, tissue damage may occur when sliding forces (shear) applied to the skin are increased. For example, shear may be increased when a patient slips down a bed or during repositioning. The friction between the patient and the support surface tends to hold the skin in place while deeper tissues are moved. This can reduce blood flow and damage tissues by crimping or closing blood vessels (International Review, 2010).
How does a support surface redistribute pressure?
The amount of pressure is related to the weight of the patient and the size of the contact area between the patient and the support surface. Support surfaces minimise pressure damage to tissues by redistributing the mechanical loads imposed on the skin and soft tissues due to patient immobility. Some support surfaces redistribute pressure by allowing the patient's body to sink into them. As the patient sinks down, more of the patient's body comes into contact with the support surface, so that the patient's weight is spread over a larger area. This produces an overall reduction in the pressure placed on the tissues.
Other support surfaces intermittently remove pressure from some areas of the body, while maintaining pressure on others. The intermittent removal of pressure allows the tissues to recover before pressure is reapplied and another area is relieved.
Types of support surfaces
Support surfaces are available as integrated bed systems, mattresses that can be fitted onto standard bed frames, overlays that are placed over existing mattresses, and seat cushions. Support surfaces can be divided into two broad categories: reactive and active.
Reactive support surfaces
A reactive support surface changes load distribution only in response to a patient lying or sitting on it. It may be powered or unpowered. The patient is able to sink into the surface, thereby increasing the area of contact with the patient's body and redistributing pressure. Examples include:
- Foam - mattresses composed of a block of foam or of layers of differing densities of foam. Foam degrades over time and may result in the patient sinking through it and onto the underlying support frame (known as 'bottoming out').
- Air- or gel-filled - surfaces comprise air or gel-filled compartments or columns.
- Low air loss support surfaces - some air-filled support surfaces allow air to escape through small holes. The air flows along the inside of a vapour permeable patient contact layer. This draws moisture and heat through the contact layer and away from the skin. This is known as 'low air loss' and may aid control of moisture on a patient's skin (International Review, 2010).
- Air-fluidised support surfaces - contain sand-like particles, such as silica beads, through which air is forced. As the air is forced through the particles, they take on the properties of a liquid (ie become fluidised). The porous cover allows air to escape out of the mattress and body fluids to flow down into the support surface.
Active support surfaces
An active support surface can change its load distribution without a patient on it, and requires a power supply. Pressure is largely redistributed through the cyclical inflation and deflation of sections of the support surface so that pressure is removed from parts of the patient and then reapplied as other parts are relieved.
Alternating pressure surfaces are currently the only form of active support surface. Repositioning of patients is as important on active support surfaces as reactive surfaces (International Review, 2010).
When should a support surface be used?
Before deciding whether a patient needs a specialised support surface, clinical judgement should be used in conjunction with a comprehensive assessment that establishes:
- Risk of pressure ulcer development - as assessed by the score derived from a pressure ulcer risk assessment tool.
- Skin condition - including whether there is any existing pressure damage and whether the patient is continent.
- Level of mobility - level of assistance required to change position in bed and with transfers and walking, use of other equipment (eg a chair, recliners or wheelchair) that may require a specialist surface
- (eg mattress, seat pad, elbow elevation pads, suspension boots).
- Care setting and the patient's and carers' knowledge of using the support surface.
- Weight and nutritional status.
- Neurological status and co-morbidities.
The selection of a support surface should not be made on the basis of a score from a pressure ulcer risk assessment tool (NICE, 2005) or on the category of any pressure damage present (NPUAP/EPUAP, 2009) alone.
All patients vulnerable to pressure ulcers, should receive as a minimum, a high specification foam mattress. Active support surfaces are recommended for patients at greater risk of developing a pressure ulcer when manual repositioning is not possible (NPUAP/EPUAP, 2009).
Overlay or mattress?
Support surface overlays are positioned on top of the existing support surface to provide additional pressure redistribution. They have the advantages of being quick and easy to fit and not requiring the existing mattress to be removed and stored elsewhere. In a home-care setting, an overlay placed on one side of the bed may also allow partners to continue sharing the same bed. However, overlays may raise the total height of the bed making getting in and out of the bed more difficult, or cause safety issues if bed rails are in use. Also, Nixon et al (2006) identified that overlays could be more expensive than mattress replacements when overall costs were considered.
Choosing a support surface
Selection of an appropriate support surface should take into account risk factors for pressure ulceration as well as patient factors, ease of use and impact on nursing procedures. It is also important to take the views of patients and carers into account when selecting a support surface. However, decisions on which support surface to choose are often limited by availability and reimbursement issues. Continued research into the effectiveness of different support systems is required to assist with decisions
about reimbursement and funding (International Review, 2010).