Pressure ulcers tend to develop on bony prominences and
on areas of the body that have little to cover them. This includes
the hips, buttocks, heels, shoulder blades and the small
of the back.
Sitting in a chair or wheelchair for long periods of time,
without pressure being relieved, is even more likely to
cause pressure ulcer development.
Pressure ulceration occurs when the skin and underlying
for a period of time, between the bone and the surface,
on which the patient is sitting or lying.
Blood cannot causing a lack of oxygen
and nutrients to the tissue cells. Furthermore, the cannot function properly
to remove waste products.
If the pressure continues, the cells die and the area of
dead tissue that results is called pressure damage.
The amount of time this takes will vary, but may develop
in as little as one hour in patients at greatest risk.
The factors causing pressure ulcers are divided
into 2 Groups
INTRINSIC - Disease, medication, malnourishment,
age, dehydration/fluid status, lack of mobility, incontinence,
skin condition, weight.
EXTRINSIC – External
influences which cause skin distortion –
Pressure, Shearing Forces, Friction, Moisture.
The blood pressure at the arterial end of the capillaries
is approximately 32 mmHg, while at the venous end this drops
The average mean capillary pressure equals about 17 mm Hg
and any external pressures exceeding this will cause capillary
Tissues that are dependent on these capillaries are deprived
of their blood supply. Eventually the ischaemic tissues
Shearing forces will only exist if pressure, usually
caused by the persons own body weight, is also present.
Shear forces occur when a part of the body tries to move
but the surface of the skin remains fixed. (See Waterlow
Manual for a better understanding of this phenomenon).
Friction forces occur when the shearing force increases
sufficiently to overcome the bodies resistance to movement.
The movement has an abrasive action.(See Waterlow
Manual for a better understanding of this action).
Skin should not be left wet as moist skin sticks
to material (e.g. bathing, perspiration, incontinence (as
urine and faeces are acidic), amniotic fluid) as it can
become macerated making it more susceptible to shear and
Certain areas of the body are more vulnerable to pressure
ulcer formation than others.
Bony prominences in particular : heels, sacrum, buttocks,
hips , elbows etc.