Pressure Ulcer Prevention and Treatment Following Spinal Cord Injury - 63

CLINICAL PRACTICE GUIDELINE

performance, heat-reducing properties (Knox et
al., 1994), adaptability, cost, care, and
maintenance needs (Krouskop et al., 1983).
Because no cushion universally produces
acceptable pressure redistribution, individualized
assessments of interface pressures, tissue
tolerance, and skin assessment are essential for
maximum protection from pressure ulcer risk
(Burns & Betz, 1999). After examining the variety
of wheelchair cushions available, health-care
professionals should determine one that matches
the individual's needs. As with bed supports, the
use of donut-shaped ring cushions should be
avoided. Sitting-acquired pressure ulcers are
caused by chronic sitting associated with central
nervous system disorders. Most manufacturers
use the interface pressures between the patient's
body and the sitting surface as the criterion for
support surfaces for beds and wheelchair
cushions. This is typically compared to the
capillary closing pressure of 32 mm Hg. This
criterion ignores the possibility that compression
forces in the muscle-bone interface can reach up
to 300 mm Hg at the ischial tuberosities (Gefen,
2007). There is no valid justification for the use
of an arbitrary threshold for applied interface
pressure. The important factors are the
combination of time, pressure and substrate, i.e.
tissue resilience.
The first study to quantify interface shear
stress, interface pressure, and cushion horizontal
stiffness was done by Akins et al. (2011). In
evaluating 21 commercial wheelchair seat
cushions, they found that interface shear stress
increased significantly with increased displacement
and that viscous fluid cushions resulted in the
least amount of interface shear stress, followed
by air cell, elastic foam, and honeycomb-type
cushions. But even the best cushion does not
alleviate the need for pressure redistribution
behaviors. Pressure-redistributing cushions include
foam, fluids, air, gel, thermoplastic cellular matrix
(honeycomb), as well as combinations of these
materials. Cushion covers are specifically designed
to work with a cushion and should not be
substituted by pillowcases, towels, plastic bags,
or other cover surfaces.
F O A M C U S H I ONS

Two types of foam, polyurethane and latex,
have been the most frequently been used to
fabricate cushions. Two common cell structures
seen are open and closed cell foams. The open
cell foams allow airflow between intertwined,
perforated membranes which allow for greater air
ventilation. Open cell foams are more likely to
absorb fluids making them more difficult for

cleaning and hygiene. Closed cell foams have
internal structures that are encapsulated in a
membrane therefore are more dense with less air
flow. They are typically used for stable bases for
other cushioning materials. Viscoelastic foam and
matrix have high viscosity and exhibit slow
accommodation with load duration. They have
"memory" and return back to their original noncompressed state in a slow fashion, which is their
hallmark trait. They present with good
envelopment and improved thermal qualities as
compared to polyurethane or latex foams. Foam
cushions are available in either a flat or contoured
design. More pliable softer foam will wrap around
the buttocks and develop more contact with body
contours (enveloping). This will result in a larger
contact area and a more uniform distribution of
pressure. Some foam material, however, may be
too soft and may result in bottoming out, or
sinking in too deeply and totally compressing the
foam, resulting in increased interface pressures.
Persons who use foam cushions should check the
ability of the foam to recover its shape when not
in use. If it appears compressed, the foam is
fatigued and will no longer redistribute the
patient's weight. Custom contoured foam
cushions are more effective than flat foam
cushions in achieving the lowest interface
pressures and the most stable base of support in
persons with SCI (Brienza et al. (1998 and 1999;
Sprigle et al. 1990). In addition to custom
contoured seat cushions, there are cushions
custom designed for complete offloading of a
bony area with redistribution at another area.
These cushions are effective for those patients
who are not able to achieve good immersion or
distribution on commercially available cushions.
AI R CUSHI ONS

Air-filled cushions are made of a sealed
compartment membrane that holds air. An airfilled cushion may have one singular air chamber
or may be divided into multiple compartments to
allow for air flow movement. These types of
cushions allow for pressure to move from high to
low pressure areas of a person's body. Air-filled
cushions allow for sinking immersion (floating) of
the buttocks into the cushion, with increasing
interface surface of the same tissue pressure.
Initial adjustments of inflation pressure are
important to establish proper immersion of the
body into the cushion. Ongoing maintenance and
vigilant assessment of cushion condition,
including inflation level, are required to ensure
adequate pressure redistribution. Bottoming out
must be avoided to prevent a rapidly forming
ulcer (Remsberg and Bennett, 1997). Postural

Pressure Ulcer Prevention and Treatment Following Spinal Cord Injury

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