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Finding a better seat cushion.

Pressure ulcers are a far too common complication from spinal-cord injury or disease (SCI/D) and a good seat cushion goes a long way in helping prevent what can be a costly, and even deadly, problem.

The Agency for Healthcare Research and Quality says the total cost for managing a single full-thickness pressure ulcer can be as high as $70,000. The agency also reports nearly 60,000 hospital patients in the U.S. are estimated to die each year from complications because of hospital-acquired pressure ulcers. Statistics such as those help show why a good seat cushion can be so valuable in preventing pressure ulcers.

There are plenty of seat cushion materials to choose from, including the widely-used and mostly inexpensive foam and more complex ones such as air-cell-based, honeycomb or gel cushions.

Despite all those choices, there's very little comparative research that's looked at which cushions are better at reducing the risk of developing a pressure ulcer.

However, a new study from Amit Gefen, PhD, at Tel Aviv University in Israel is shedding some light.

Comparing Foam vs. Air

Gefen is a biomedical engineer and the current president of the European Pressure Ulcer Advisory Panel.

His work has helped provide new insight into an especially dangerous and difficult to detect kind of pressure ulcer, the kind caused by deep tissue injury (DTI).

Specifically, Gefen has shown that the primary cause of DTIs isn't so much lack of blood flow (ischemia), which was the conventional wisdom, but tissue and cell deformation. Ischemia is only secondary.

The newest study from Gefen's lab reveals important insights about reducing these deformations and preventing DTIs.

It offers the first comparison of how two commonly used cushion technologies--foam-based and air-cell-based --stack up with respect to tissue deformation.

Measuring Performance

The research was published in the February 2014 issue of the journal of Tissue Viability. I partnered with Gefen and graduate student Ayelet Levy to author the article.

To understand what happens deep within the body where DTIs occur Gefen recommended a sophisticated tool that evaluates internal soft tissue loads in the buttocks. The tool is called finite element modeling.

Using computer models to predict mechanical stress and strain outcomes, it's been employed before to analyze the biomechanical performances of basic foam cushions. But it had never been used to measure the performance of an air-cell-based cushion.

Gefen suggested comparing the air-cell cushion with two flat, foam-based cushions of different stiffness levels for a patient with SCI/D. It's been estimated that roughly 60% of all patients with SCI/D will develop a potentially deadly pressure ulcer.

The project started by developing an anatomically realistic model of a 21-year-old SCI/D patient's left buttock. The lab then created 15 variants of the model, representing the different kinds of muscle atrophy, spasticity and bone-flattening that patients with SCI/D undergo as they live their lives seated.

Examining Immersion

The next step was to examine "immersion," or the percentage of skin surface in full contact with the cushion for all three cushions.

Higher numbers are better here because the more surface area involved in load transfer, the lower the loads will be in the tissues.

Gefen's team then looked at all four kinds of mechanical stresses that come into play in these conditions, and measured those stresses in the muscle, fat and skin tissues under the sitting bones of the pelvis for all 15 models. In that way, it was possible to determine the risks for the specific internal deformations.

The results were stunning. The air-cell-based cushion immersion registered consistently in the 91-93% range; for the foam cushions, it was 58-65%.

All four of the peak stress components were 10,000 times lower for all three kinds of tissues in the air-cell-based cushion than for the foam models.

Not only that, but the tests on the bone flattening and muscle atrophy models showed that as the patient's condition worsens over time, the favorable spread between the performances of the air-cell-based cushion and the foam supports just gets bigger.

Minimizing Deformations

More research is needed, but these findings suggest air-cell-based cushions provide much longer safe-sitting times than foams for wheelchair cushion users.

The findings also suggest the need for new wheelchair cushion health care policies. The current standards don't protect as they should. They don't distinguish among the different cushion types according to how well they minimize tissue deformations.

Even cushions categorized as "skin protection cushions" can present a wide range of risks or protection, since they're not categorized by how well they minimize tissue deformations.

That can lead some clinicians to recommend wheelchair cushions to users based only on price. Buying a seat cushion based on price alone without evaluating patient risk is shortsighted and can lead to trouble down the road.

Kara Kopplin is senior director of efficacy research, standards and compliance at wheelchair seating systems manufacturer ROHO, Inc., which funded Amit Gefen's research.
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Title Annotation:research update
Author:Kopplin, Kara
Publication:PN - Paraplegia News
Date:Dec 1, 2014
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