Icon I4 Acute Care 250kg

For tissue damage to occur, the coefficient must be at a level high enough to create drag that will injure the superficial layers. Decreased levels of friction allow the surfaces to easily slide across each other. Too much friction and there is no movement at all.

Shear is a different subject that incorporates friction and another force, usually gravity or inertia. Shear is often described as an internal opposing motion of tissue and bone created when a patient is sitting up in bed. Gravity affects all tissues or skin layers, pulling them down in a slow, gradual manner. Simultaneously, the skin interacts with the sheets creating friction. As the bone is pulled down by gravity and the skin is in essence ‘pulled up’ by the sheet, the subcutaneous tissue and muscle are caught in between, literally pulled in opposite directions, leading to shear. This pulling creates stress on the soft tissue layers (fat and muscle) and potentially could lead to tearing of the tissue – depending on how high the shearing force becomes. The greatest stress is also now applied to the two tissues that are the least tolerant of ischemia from the concurrent pressure from sitting. Shearing forces are greater over the sacrum, gluteal and ischial areas of the body.

Both friction and shear are affected by moisture. Dry conditions reduce friction.

How the wound or injury developments in these scenarios –

The force from shear or friction will cause the skin and/or deeper tissues to distort and deform, which will result in strain and stress within the tissue. Excessive internal strains and stresses lead to damage to the cell structures such as the cytoskeleton and may hinder transport processes within the tissues such as reducing blood perfusion.

An effective pressure reducing support surface must reduce both shear and friction forces, as well as manage moisture, to reduce the risk of pressure injuries.

The Sovereign S6 has been designed to reduce sheer & friction forces by using the following mattress technologies:

• Super Sheer Inner Cover – high stretch lycra cover that sits below the outer cover to act as a buffer between the friction or shearing force exerted by movements in the support surface and the individual. As such, instead of the mattress cover (which is usually a polyurethane – a high coefficient of friction) rubbing against the client’s skin when they are changing position in bed, the mattress cover rubs against the inner cover, and the client can slide with minimal frictional or shearing forces. It is important to note that the Super Sheer cover is fully breathable to ensure the micro-climate is managed.
• Premiflex Ultra Outer Cover – made from a four-way stretch polyurethane. Pressure care covers must have a minimum of two-way stretch to reduce the coefficient of friction and the potential forces of shearing & friction.
• Hinged strengthened sides – the firm strengthened sides have been engineered to have hinges located in the knee and back break to allow the mattress to conform easily to a profiling bed. Without these hinges, the mattress will create friction when profiling.
• All micro-climate management related features also reduce tension and the risk of shear/friction related injuries

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Reactive support surfaces come in many different types including:

• Foam – mattress composed of foam or layers of foam with different densities and shapes. For example, Forté Icon Medium Care Mattresses.
• Air or Gel Filled – surfaces comprise air or gel-filled compartments. For example, ROHO Integrated Systems.
• Hybrid – surface combining foam and air technology to maximise the benefits offered by both static and alternating surfaces.
• Low air loss – 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. Low air loss aids control of moisture on a patient’s skin.
• Air-fluidised – contain sand-like particles through which air is forced. As the air is forced through the particles, they take on the properties of a liquid. The porous cover allows air to escape out of the mattress and body fluids to flow down into the support surface

“Pressure redistribution is achieved by either increasing the body surface area that comes in contact with the support surface through immersion and envelopment (to reduce concentrations of weight over bony prominences) or sequentially altering the parts of the body that bear the load, thus reducing the duration of loading at any given anatomical site”. Prevention and Treatment of Pressure Injuries: Clinical Practice Guideline. The International Guideline 2019.

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