What Is a Failed or Compromised Skin Graft?
Skin grafting, including skin substitutes, is a procedure to reconstruct a skin defect that cannot fill in on its own or in which primary closure cannot be done. This is important, as the skin offers protection from the elements and infectious organisms, as well as temperature control and other functions.
There are several layers of skin, the uppermost having the most keratin. The top layer, the epidermis, is made to experience the elements and designed for loss and regeneration.
- Split-thickness graft: is composed of the top layer of skin, the epidermis, and some of the next layer, the dermis. Because some dermis is left, the donor area can heal. This is preferred for large areas and has the advantage of allowing harvesting. The success “take” rate for split-thickness grafts is 95%.
- Full-thickness graft: has all skin layers. This also has a success rate of 95%.
Autograft refers to transfer of skin (split-thickness or full-thickness) from one site to another on the same person. This eliminates immunological rejection issues. Capillaries from the site upon which the autograft is grafted restore blood supply over the first 3 days and full circulation is expected in 4-7 days. A split thickness donation leaves dermis behind, allowing it to heal, but the transplanted skin is delicate and can contract (contracture). A full thickness donation leaves an additional defect at the site from which the graft was procured; this is closed by approximating the edges of the new defect. In spite of this, a full thickness donation offers a better result with its smoothness and flexibility and better protection because of its thickness, but fails more frequently due to fluid accumulation and impaired drainage.
Allografts are harvested from others, making the graft genetically different from the recipient. Included in the allograft category is human amniotic membrane which contains growth factors that promote healing. Allografts are used primarily in burn patients. The immune reaction to allografts is diminished by “decellularizing” the tissue of its epidermal and cellular components.
Xenografts use porcine tissue, which constitutes grafting from an unrelated species. It is used for temporary skin coverage of expansive areas, such as occurs in burns. They are always available, but they are not as successful as allografts.
When a wound is not well vascularized, a flap is used to improve the chances of success. A flap, a section of pivoted tissue from an well-vascularized adjacent area, enhances neovascularization and also allows the cosmetic advantage of healing with similar pigmentation.
Biosynthetic material can be temporarily used to protect clean wounds from drying (desiccation). They generally separate once reepithelialization has occurred.
The thinner the graft, the more likely it will contract. Choice of what type of graft is used must strike a balance between contracture of thin grafts vs. the increased vascularity a thicker graft requires.
How Is a Failed or Compromised Skin Graft Diagnosed?
There are many reasons that grafts can fail. Scrupulous surveillance of a graft includes serial inspection of both the donor site (in autografts) and the graft (recipient) site. Such surveillance is necessary to diagnose any processes that may contribute to a graft’s failure:
● Poor vascularity.
Vascular compromise can be diagnosed by inspection for color change, diminished capillary refill, temperature, edema, and general appearance.
● Hematoma or seroma, i.e., collections of blood or fluid, respectively.
Blood or transudate (exudate, in the case of infection) can be diagnosed via aspiration with a needle. The retrieved contents are examined microscopically for red blood cells, white blood cells, and bacteria (via a gram stain). The aspirate also can be cultured for sensitivity testing of any positive bacterial growth. Aspiration also allows the therapeutic benefit of reducing separation between the graft and the wound bed.
● Infection of graft site.
The most common infectious organisms are methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus, or Pseudomonas.
If infection is suspected, diagnosis is via cultures from the graft site, retrieved to identify any infecting organism with subsequent testing for its sensitivities to several antibiotics.
● Mechanical shearing.
The most common cause of graft failure is movement, which dissociates any new blood vessel growth (neovascularization) into the graft, depriving it of oxygen and nutrients. This complication causes fluid collection between the graft and the graft site bed (hematoma or seroma), further separating the graft from the bed. Immobilization is accomplished by appropriately dressing the graft site.
Hypertrophic Scarring (Keloid Formation)
All grafted areas will scar to some extent, and a scar is not deemed “mature” until a year after grafting. Any scar that is raised above skin level is considered hypertrophic. Such keloid formation is diagnosed via simple inspection.
Management of Failed or Compromised Skin Graft
Partial graft loss can be treated with wet or moist saline-soaked gauze or other local dressings. If salvaging the graft is successful to any extent, the defect can be allowed to heal secondarily (filling in). Re-grafting must take into consideration the reasons the first graft failed.
Complete graft loss requires reassessment of the wound bed for blood supply. If the bed is poorly vascularized, thinner grafts can be used which have less of a neovascularization demand. If the wound bed is well vascularized, re-grafting can be attempted with a thicker graft.
Choice of dressing is usually by physician preference, but the dressing should be non-adherent. Transparent plastic wound dressings allow inspection of the wound. They are generally atraumatic and can be be covered with silver nitrate or iodine soaks.
Moist dressings typically have less pain and infection, improving the quality of healing.
Bandaged graft sites will become dry, therefore moisturizer should be applied at least daily after bandage removal.
Immobilization of the graft prevents shearing of it and the resulting accumulation of hematoma or seroma fluid under it, the main contributor to neovascularization failure.
In autografts, the additional wound–the donor site–is evaluated every 3 days until healed.
Prevention of Failed or Compromised Skin Graft
Preventing graft failure or compromise is by scrupulous surveillance to identify as early as possible the following:
- Poor vascularity
- Hematoma or seroma
- Mechanical shearing
Pre-graft, these complications can be prevented by proper wound bed preparation. During the grafting, complications can be reduced with intraoperative meticulous hemostasis and careful placement of the graft. After the procedure, immobilization is used with appropriate dressing to prevent shearing during the healing period.
Comorbidities that negatively impact neovascularization and healing should be addressed before the procedure to give the graft the best opportunity to “take” (proper adhesion) and the site to heal. This entails strict glycemic control for diabetics, smoking cessation, and correcting any protein or vitamin deficiencies. Medications that interfere with wound healing (steroids, immunosuppressants, and anticoagulants) should be discontinued temporarily.
In full-thickness skin grafts, the wound should be debrided where necessary and inspected for shearing or infection. Any fluid collections should be drained via creating small perforations and aspiration, which has the added benefit of diagnosing infection via retrieval of material to culture.
After about 2 weeks, the epithelium of a skin graft should be intact and scar prevention measures begin. Silicone covering and pressure therapy are applied to prevent hypertrophy (keloid). This protocol should be continued for 3 months.