Alternating pressure, defined as pressure redistribution via cyclic changes in loading and unloading is the recommended bed support surface feature. When at risk or ulcerated patients cannot be repositioned manually, active support surfaces are needed, as they can change their load-distribution properties and help make sure blood is getting to the skin. Generally, the less time between cycles the better for load-distribution and blood flow, so it is best to alternate more, as tolerated.
Some bed support surfaces offer pulsation instead of alternating pressure. Pulsation differs from alternation in that the duration of peak inflation is shorter and the cycling time is more frequent. For example, Medicalairmattress.com's True Low Air Loss Hospital Mattress pulsation mode reduces air flow every 30 seconds to 50% of the comfort setting. Pulsation is theorized to increase lymphatic drainage (may decrease swelling) and blood flow by having a "massaging" benefit. It may also enhance patient comfort and relieve pain.
Pain due to lying down or sitting with or without limited ability to reposition can be lessened by using support surfaces for beds and wheelchairs that provide Immersion and envelopment. Immersion is the depth of penetration or "sinking" into the support surface. Envelopment is the ability of the support surface to conform to the body parts sinking into it. Sitting tolerance can also be increased and pain decreased by making sure a proper back is used in a wheelchair, not just a pressure redistributing cushion. The sling fabric on any wheelchair is there so the wheelchair folds; not to support a human trunk or pelvis.
Many bed support surfaces are described as Low Air Loss (LAL) or True Low Air Loss (TLAL). Low Air Loss is a feature of a support surface that provides a flow of air to assist in managing the heat and humidity (microclimate) of the skin. If you or your patient are very diaphoretic (perspiring profusely) or always hot or cold, Low Air Loss may help. Low Air Loss can be achieved with compressors pumping as little as 4 liters per minute (LPM) of air or with blowers producing over 1000 LPM of air. While there is no consensus on the definition of true low air loss, it is generally used to describe blower based, rather than compressor or pump based systems.
A blower is capable of transferring or wicking more moisture vapor away from the patient than a pump, helping to maintain the microclimate or proper skin temperature and humidity.
