Burn Care/Skin Grafts
A first degree or superficial burn heals naturally through the body's ability
to replace damaged skin cells. Deep second and full thickness burns require skin
graft surgery for quick healing and minimal scarring. In the case of large burn
size, patients will need more than one operation during a hospital stay.
Patients may need surgery for surgical debredement (cleaning). Skin grafting is
also done in surgery, which consists of excision or the surgical removal of burn
injured tissue; choosing a donor site, or an area from which healthy skin is
removed to be used as cover for the cleaned burned area; and harvesting, where
the graft is removed from the donor site by an instrument similar to an electric
shaver. This instrument (dermatome) gently shaves a piece of skin, about 10/1000
of an inch thick, off the unburned area. Finally, the surgeon places and secures
the skin graft over the surgically cleaned wound so that it can heal. Skin
donated by other people who have died (called homograft, allograft, or cadaver
skin) is sometimes used as a temporary cover for a burned area that has been
cleaned. To help the graft heal and become secure, the area of the graft is not
moved for five days following each surgery (immobilization period). During this
immobilization period, blood vessels begin to grow from the tissue below into
the donor skin, bonding the two layers together. Five days after grafting,
exercise therapy programs, tub baths and other normal daily activities resume.
During surgery an anesthetic is used. An anesthetic is a substance that produces
loss of feeling. A general anesthetic does this by making the patient
unconscious. Some anesthetics are given by injection into a vein (intravenous
injection) and others are given as a gas mixture, which is breathed into the
lungs and then absorbed into the bloodstream.
Often burn patients need blood transfusions to replace blood lost during
surgery. Blood transfusions increase the red blood cells, which carry oxygen
from the lungs to every part of the body and take waste in the form of carbon
dioxide back to the lungs, where it is breathed out into the air. If there
aren't enough red blood cells or if the cells do not contain enough iron to
carry oxygen properly, wounds do not heal as well.
There are a variety of skin grafts, some that provide temporary cover and others
that are for permanent wound coverage.
Temporary Wound Covering
Allograft, Cadaver Skin, or Homograft is human cadaver skin donated for medical
use. The clinical use of allograft skin in the modern era was popularized by
James Barrett Brown, who described its use in 1942. Cadaver skin is used as a
temporary covering for excised (cleaned) wound surfaces before autograft
(permanent) placement. Unmeshed cadaver is put over the excised wound and
stapled in place. Post-operatively, the cadaver may be covered with a dressing.
Wound coverage using cadaveric allograft is removed prior to permanent
autografting.
Xenograft or Heterograft is skin taken from a variety of animals, usually a pig.
Heterograft skin became popular because of the limited availability and high
expense of human skin tissue. In some cases religious, financial, or cultural
objections to the use of human cadaver skin may also be factors. Wound coverage
using xenograft or heterograft is a temporary covering used until autograft.
Porcine is commonly used as temporary skin coverage for Exfoliative Skin
Diseases (e.g. SJS, TEN).
Permanent Wound Covering
Autograft is skin taken from the person burned, which is used to cover wounds
permanently. Since the skin is a major organ in the body, a autograft is
essentially an organ transplant. Autograft is surgically removed using a
dermatome (a tool with a sharp razor blade). A dermatome sheers the donor skin
off the body. Only the top layer of skin is used for donor skin. Donor skin is
taken at such a depth where the site will heal on its own, very similar to a
second degree burn. There are two types of autografts used for permanent wound
coverage: sheet grafts and meshed grafts.
Sheet Graft is piece of donor skin is removed from an unburned area of the body,
a process called "harvesting the donor." The size of the donor skin that is used
to patch a burned area is about the same size as the burn size. The donor sheet
is laid over the excised wound and stapled in place. The donor skin used in
sheet grafts does not stretch; it takes a slightly larger size of donor skin to
cover the same burn size area because there is slight shrink after harvesting.
When the body surface area of the burn is large, sheet grafts are saved for the
face, neck and hands, making the most visible parts of the body appear less
scarred. When a burn is small and there is plenty of donor skin available, a
sheet graft is usually used to cover the entire burned area. The disadvantages
of sheet grafts are that small areas of graft might be lost from build up of
fluid (hematoma) under the sheet right after surgery. Sheet grafts also create a
larger donor site than meshed skin. A sheet graft is usually more durability and
scars less.
Meshed Skin Grafts very large areas of open wounds are difficult to cover
because there might not be enough unburned donor skin available. In these large
wounds it is necessary to enlarge donor skin to cover a larger body surface
area. Meshing is a means to enlarge donor skin. Meshing involves running the
donor skin through a machine that makes small slits, which allows expansion
similar to that in fish netting. In a meshed skin graft, the skin from the donor
site is stretched to allow it to cover an area larger than itself. The size of
the mesh varies in ratios from 1:1 to 1:4. A 1:1 mesh has small slits that allow
the donor skin to expand one times its original size. Likewise, a 2:1 mesh has
slightly larger slits that allow the donor to be enlarged two times the size of
the skin that has been harvested. Most donor skin is meshed at a 1:1 or 1:2
ratio because the larger the size mesh the more fragile the graft. No matter
what size meshing is used, healing occurs as the spaces between the mesh, called
the intricities, fill in with new epithelial skin growth. The disadvantages of
meshing are that it is a less durable graft than a sheet graft and that the
larger the mesh, the greater the permanent scarring. Meshing serves two
purposes: it allows blood and body fluids to drain from under the skin grafts,
preventing graft loss; and it allows the donor skin to cover a greater burned
area because it is expanded.
Allograft, cadaver skin, or homograft is ordered from the local skin bank.
Xenograft, or animal skin, is ordered from a medical supply company. Autograft
is surgically removed from the patient using a dermatome.
