C h a p t e r 4 6
Disorders of Skin Integrity and Function
1171
A split-thickness skin graft can be sent through a skin
mesher that cuts tiny slits into the skin, allowing it to
expand up to nine times its original size. These grafts
are used frequently because they can cover large surface
areas and there is less autorejection.
Full-thickness skin
grafts
include the entire thickness of the dermal layer.
They are used primarily for reconstructive surgery or
for small deep areas. The donor site of a full-thickness
skin graft requires a split-thickness skin graft to help
it heal.
Two-layered synthetic skin grafts, such as
Apligraf
or
Integra
, are composed of a layer of silicone, mim-
icking the properties of the epidermis, and a layer
or matrix of fibers.
52
Skin cells attach to the fibers,
enabling dermal skin growth. Once the dermal skin has
regenerated, the silicone layer is removed and a thin
epidermal skin graft is applied, thus requiring less skin
grafting overall.
Other treatment measures include positioning, splint-
ing, and physical therapy to prevent contractures and
maintain muscle tone. Because the normal body response
to disuse is flexion, the contractures that occur with a
burn are disfiguring and cause loss of limb or appendage
use. Once the wounds have healed sufficiently, elastic
pressure garments, sometimes for the full body, often
are used to prevent hypertrophic scarring.
Pressure Ulcers
Pressure ulcers are ischemic lesions of the skin and
underlying structures caused by unrelieved pressure
that impairs the flow of blood and lymph. Pressure
ulcers often are referred to as decubitus ulcers or bed-
sores. The word decubitus comes from the Latin term
meaning “lying down.” However, a pressure ulcer may
result from pressure exerted when seated or lying down.
Pressure ulcers are most likely to develop over a bony
prominence, but they may occur on any part of the body
that is subjected to external pressure, friction, or shear-
ing forces.
Approximately 2.2 million people in the United States
develop pressure ulcers annually.
53
Several subpopula-
tions are at particular risk, including persons with quad-
riplegia, elderly persons with restricted activity and hip
fractures, and persons in the critical care setting.
Mechanisms of Development
Many factors contribute to the development of pressure
ulcers, such as length of stay in the hospital, vasopres-
sure infusion, spinal cord injury, age, and body mass
index.
54
Pressure, shearing forces, friction, and moisture
contribute to the incidence of pressure ulcers. External
pressures that exceed capillary pressure interrupt blood
flow in the capillary beds. When the pressure between
a bony prominence and a support surface exceeds the
normal capillary filling pressure, capillary flow essen-
tially is obstructed. If this pressure is applied constantly
for 2 hours, oxygen deprivation coupled with an accu-
mulation of metabolic end products leads to irreversible
tissue damage. While pressure magnitude and duration
are important in the creation of a pressure ulcer, no spe-
cific amount of pressure necessary to compress capil-
laries and interrupt blood flow has been determined.
55
Tolerance to pressure loads differs according to tissue,
location, and metabolism.
55
Persons with impaired cir-
culation require less pressure to interrupt circulation.
The same amount of pressure causes more damage when
it is distributed over a small area than over a larger area.
Whether a person is sitting or lying down, the weight
of the body is borne by tissues covering the bony promi-
nences. Most pressure ulcers are located on the lower part
of the body, such as the sacrum, the coccygeal area, the
ischial tuberosities, and the greater trochanters. Pressure
over a bony area is transmitted from the surface to the
underlying dense bone, compressing all of the interven-
ing tissue. As a result, the greatest pressure occurs at the
surface of the bone and dissipates outward in a cone-
like manner toward the surface of the skin (Fig. 46-19).
Thus, extensive underlying tissue damage can be present
when a small superficial skin lesion is first noticed.
Altering the distribution of pressure from one skin
area to another prevents tissue injury. Pressure ulcers
most commonly occur in persons with conditions such
as spinal cord injury in which normal sensation and the
ability to move to redistribute body weight are impaired.
Normally, persons unconsciously shift their weight to
redistribute pressure on the skin and underlying tis-
sues. For example, during the night, people turn in their
sleep, preventing ischemic injury of tissues that overlie
the bony prominences that support the weight of the
body; the same is true for sitting for any length of time.
Pressure
Epidermis
Dermis
Skin
Deep fascia
Muscle
Periosteum
Bone
Subcutaneous
fat
FIGURE 46-19.
Pressure over a bony prominence
compresses all intervening soft tissue, with a resulting
wide, three-dimensional pressure gradient that causes
various degrees of tissue damage. (From Shea JD.
Pressure sores: classification and management. Clin
Orthop Relat Res. 1975;112:90.)
