INTERNATIONAL
COLLABORATION TO DEFINE AND MEASURE SHEAR
FOR
almost fifty years shear forces have been strongly implicated
in the aetiology of pressure ulcers. However, quantitative measurement
of shear remains challenging with the introduction of a sensor
likely to change the magnitude and perhaps orientation of forces
acting parallel to the skin surface. While measurement is problematic
for many clinicians the definition of shear and shear forces is
unclear with the term ‘shear’ often being used interchangeably
with ‘friction’. At the close of the 8th Open Meeting
of the EPUAP (Aberdeen, Scotland, May 2005) a new international
initiative was launched to clarify both the definition of shear
and to investigate its measurement. This initiative draws together
members from the EPUAP, the US National Pressure Ulcer Advisory
Panel (NPUAP) and the Japanese Pressure Ulcer Society, along with
representatives
from the wound care industry. In April 2006 this group met in
San Antonio, Texas and this report describes the current status
of the initiative following the recent meeting in the United States.
Currently there are forty-seven individuals signed up to taking
part in the shear force initiative with nineteen attending the
meeting in San Antonio. Please contact Dr Denis Colin at <dcolin@ch-arche.fr>
if you would like to participate in this important activity. The
meeting was divided into two sections – a general group
discussion centered upon three presentations – two of these
were focused upon shear measurement and the effect of shear on
skin blood flow and delivered by colleagues from the Japanese
Pressure Ulcer Society with the third presentation showing shear
related tissue damage. The afternoon saw the group divide into
two sections – one looking at the definition of shear and
its clinical relevance. The second group explored shear measurement
and its relationship with other parameters such as blood flow.
The definition group identified four terms that required clear,
explicit definition to assist clinicians. These terms were shear,
friction,
Above:
Some of the members of the shear force initiative who
attended the recent meeting in San Antonio, Texas, USA.
pressure,
and coefficient of friction. The working definition for each of
these terms is shown below and will be debated during the EPUAP
Open Meeting to be held in Berlin in late August. If you have
comments regarding these definitions please send them to the EPUAP
at: epuap@aol.com.
Shear:
An action or stress resulting from applied forces which causes
or tends to cause two contiguous internal parts of the body to
deform in the transverse plane (i.e., shear strain).
Pressure:
The force per unit area exerted perpendicular to a surface.
Friction:
The resistance to motion of the external tissue sliding in a parallel
direction relative to the support surface resulting in external
tissue damage.
Coefficient of Friction:
A measurement of the amount of friction existing between two surfaces
for a given force tending to hold the surfaces
together. The second working group considered the technical parameters
that would have to be measured in order to quantify shear between
the skin and soft tissue and an external support surface. One
key challenge is that information is
likely to be needed at different interfaces – between the
skin and the support surface but also between internal soft tissue
layers. Initial discussions also explored how to define test criteria
that could be used to directly compare different sensor systems
intended to measure shear forces.
The next meeting of this international initiative will be held
on Sunday 3 September in Berlin and the shear force
initiative members hope to welcome new participants at this gathering.
There will also be a scientific session during the
EPUAP conference where the work of the group will be discussed
along with presentations upon the measurement of shear.
