A wound is a disruption in the continuity of cells—anything that causes cells that would normally be connected to become separated. Wound healing is the restoration of that continuity. Several effects may result with the occurrence of a wound: immediate loss of all or part of organ functioning, sympathetic stress response, hemorrhage and blood clotting, bacterial contamination, and death of cells. The most important factor in minimizing these effects and promoting successful care is careful asepsis, which can be accomplished using aseptic techniques when treating a wound.
Wound healing is a biological process that begins with trauma and ends with scar formation. There are two types of tissue injury: full and partial thickness. Partial thickness injury is limited to the epidermis and superficial dermis, with no damage to the dermal blood vessels. Healing occurs by regeneration of other tissues. Full thickness injury involves loss of the dermis extends to deeper tissue layers, and disrupts dermal blood vessels. Wound healing involves the synthesis of several types of tissue and scar formation.
The three phases of repair are lag, proliferative, and remodeling. Directly after injury, hemostasis is achieved with clot formation. The fibrin clot acts like a highway for the migration of cells into the wound site. Within the first four hours of injury, neutrophils begin to appear. These inflammatory cells kill microbes, and prevent the colonization of the wound. Next the monocyte, or macrophage, appears. Functions of these cells include the killing of microbes, the breakdown of wound debris, and the secretion of cytokines that initiate the proliferative phase of repair. Synthetic cells, or fibroblasts, proliferate and synthesize new connective tissue, replacing the transitional fibrin matrix. At this time, an efficient nutrient supply develops through the arborization (terminal branching) of adjacent blood vessels. This ingrowth of new blood vessels is called angiogenesis. This new and very vascular connective tissue is referred to as granulation tissue.
The first phase of repair is called the lag or inflammatory phase. The inflammatory response is dependent on the depth and volume of tissue loss from the injury. Characteristics of the lag phase include acute inflammation and the initial appearance and infiltration of neutrophils. Neutrophils protect the host from microorganisms and infection. If inflammation is delayed or stopped, the wound becomes susceptible to infection and closure is delayed.
The proliferative phase is the second phase of repair and is anabolic in nature. The lag and remodeling phase are both catabolic processes. The proliferative phase generates granulation tissue. In this process, acute inflammation releases cytokines, promoting fibroblast infiltration of the wound site, then creating a high density of cells. Collagen is the major connective tissue protein produced and released by fibroblasts. The connective tissue physically supports the new blood vessels that form and endothelial cells promote ingrowth of new vessels. These new blood vessels are necessary to meet the nutritional needs of the wound healing process. The mark of wound closure is when a new epidermal cover seals the defect. The process of wound healing continues beneath the new surface. This is the remodeling or maturation phase and is the third phase in healing.
The first principle of wound care is the removal of nonviable tissue, including necrotic (dead) tissue, slough, foreign debris, and residual material from dressings. Removal of nonviable tissue is referred to as debridement ; removal of foreign matter is referred to as cleansing. Chronic wounds are colonized with bacteria, but not necessarily infected. A wound is colonized when a limited number of bacteria are present in the wound and are of no consequence in the healing process. A wound is infected when the bacterial burden overwhelms the immune response of the host and bacteria grow unchecked. Clinical signs of infection are redness of the skin around the wound, purulent (pus-containing) drainage, foul odor, and edema.
The second principle of wound care is to provide a moist environment. This has been shown to promote reepithelialization and healing. Exposing wounds to air dries the surface and may impede the healing process. Gauze dressings provide a moist environment provided they are kept moist in the wound. These are referred to as wet-to-dry dressings. Generally, a saline-soaked gauze dressing is loosely placed into the wound and covered with a dry gauze dressing to prevent drying and contamination. It also supports autolytic debridement (the body's own capacity to lyse and dissolve necrotic tissue), absorbs exudate, and traps bacteria in the gauze, which are removed when the dressing is changed.
Preventing further injury is the third principle of wound care. This involves elimination or reduction of the condition that allowed the wound to develop. Factors that contribute to the development of chronic wounds include losses in mobility, mental status changes, deficits of sensation, and circulatory deficits. Patients must be properly positioned to eliminate continued pressure to the chronic wound. Pressure reducing devices, such as mattresses, cushions, supportive boots, foam wedges, and fitted shoes can be used to keep pressure off wounds.
Providing nutrition, specifically protein for healing, is the fourth principle of healing. Protein is essential for wound repair and regeneration. Without essential amino acids, angiogenesis, fibroblast proliferation, collagen synthesis, and scar remodeling will not occur. Amino acids also support the immune response. Adequate amounts of carbohydrates and fats are needed to prevent the amino acids from being oxidized for caloric needs. Glucose is also needed to meet the energy requirements of the cells involved in wound repair. Albumin is the most important indicator of malnutrition because it is sacrificed to provide essential amino acids if there is inadequate protein intake.
Effective wound care begins with an assessment of the entire patient. This includes obtaining a complete health history and a physical assessment. Assessing the patient assists in identifying causes and contributing factors of the wound. When examining the wound, it is important to document its size, location, appearance, and the surrounding skin. The health care professional also examines the wound for exudate, necrotic tissue, signs of infection, and drainage, and documents how long the patient has had the wound. It is also important to know what treatment, if any, the patient has previously received for the wound.
Actual components of wound care include cleaning, dressing, determining frequency of dressing changes, and reevaluation. Dead tissue and debris can impede healing: the goal of cleaning the wound is its removal. When cleaning the wound, protective goggles should be worn and sterile saline solution should be used. Providone iodine, sodium hypochlorite, and hydrogen peroxide should never be used, as they are toxic to cells.
Gentle pressure should be used to clean the wound if there is no necrotic tissue. This can be accomplished by utilizing a 60 cc catheter tip syringe to apply the cleaning solution. If the wound has necrotic tissue, more pressure may be needed. Whirlpools can also be used for wounds having a thick layer of exudate. At times, chemical or surgical debridement may be needed to remove debris.
Dressings are applied to wounds for the following reasons: to provide the proper environment for healing, to absorb drainage, to immobilize the wound, to protect the wound and new tissue growth from mechanical injury and bacterial contamination, to promote hemostasis, and to provide mental and physical patient comfort. There are several types of dressings and most are designed to maintain a moist wound bed:
- Alginate: Made of non-woven fibers derived from seaweed, alginate forms a gel as it absorbs exudate. It is used for wounds with moderate-to-heavy exudate or drainage, and is changed every 12 hours to three days, depending on when the exudate penetrates the secondary dressing.
- Composite dressings: Combining physically distinct components into a single dressing, composite dressings provide bacterial protection, absorption, and adhesion. The frequency of dressing changes vary.
- Foam: Made from polyurethane, foam comes in various thicknesses having different absorption rates. It is used for wounds with moderate-to-heavy exudate or drainage. Dressing change is every three to seven days.
- Gauze: Available in a number of forms including sponges, pads, ropes, strips, and rolls, gauze can be impregnated with petroleum, antimicrobials, and saline. Frequent changes are needed because gauze has limited moisture retention and properties, and there is little protection from contamination. With removal of a dried dressing, there is a risk of wound damage to the healing skin surrounding the wound. Gauze dressings are changed two to three times a day.
- Hydrocolloid: Made of gelatin or pectin, hydrocolloid is available as a wafer, paste, or powder. While absorbing exudate, the dressing forms a gel. Hydrocolloid dressings are used for light-to-moderate exudate or drainage. This type of dressing is not used for wounds with exposed tendon or bone, third-degree burns, or in the presence of bacterial, fungal, or viral infection or active cellulitis or vasculitis because it is almost totally occlusive. Dressings are changed every three to seven days.
- Hydrogel: Composed primarily of water, hydrogel dressings are used for wounds with minimal exudate. Some are impregnated in gauze or non-woven sponge. Dressings are changed one or two times a day.
- Transparent film: An adhesive, waterproof membrane that keeps contaminants out while allowing oxygen and water vapor to cross through, it is used primarily for wounds with minimal exudate. It is also used as a secondary material to secure non-adhesive gauzes. Dressings are changed every three to five days if the film is used as a primary dressing.
In cases where a wound is particularly severe, large, or if it is a third degree burn, cellular wound healing products may be used to close the wound and speed recovery. In some cases (i.e., a third-degree burn), a skin graft will often be used. Although most surgeons prefer to use skin donated from another person (known as cadaver skin, or human allograft), skin donations are not always available. They must rely on more recent products available, such as cellular wound dressings, for the treatment of burns. For skin grafting of full-thickness burn wounds, surgeons use healthy skin from another part of the person's own body (autografting) as a permanent treatment. Surgeons may use cellular wound dressings as a temporary covering when the skin damage is so extensive that there is not enough healthy skin available to graft initially. This helps prevent infection and fluid loss until autografting can be performed.
The survival rate for burn patients has increased considerably through the process of quickly removing dead tissue and immediately covering the wound. Burns covering half the body were routinely fatal 20 years ago but today, even people with extensive and severe burns have a good chance of survival, according to the American Burn Association.
Cellular wound dressings
In recent years, the technology of burn and wound care using cellular wound dressings and grafts are helping to transform the treatment of burns and chronic wounds by decreasing the risk of infection, protecting against fluid loss, requiring fewer skin grafts, and promoting and speeding the healing process. These dressings provide a cover that keeps fluids from evaporating and prevents blood from oozing out once the dead skin has been removed. Some of these products grow in place and expand natural skin when it heals.
Cellular wound dressings may look and feel like skin, but they do not function totally like skin because they are missing hair follicles, sweat glands, melanocytes, and Langerhans' cells. Some cellular wound dressings have a synthetic top layer structured like an epidermis. It peels away over time, or is replaced with healthy skin through skin grafting. How these products are involved in wound repair is a subject of great scientific interest; it is known that they promote a higher rate of healing than does standard wound care.
People with severe wounds, chronic wounds, burns, and ulcers can benefit from cellular wound dressings. Several artificial skin products are available for nonhealing wounds or burns such as: Apligraft® (Norvartis), Demagraft®, Biobrane®, Transcyte® (Advance Tissue Science), Integra® Dermal Regeneration Template® (from Integra Life Sciences Technology), and OrCel®.
- Apligraf is a two-layer wound dressing that contains live human skin cells combined with cow collagen. It delivers live cells from a different donor (circumcised infant foreskin). Thousands of pieces of Apligraf are produced in the laboratory from one small patch of cells from a single donor.
- Dermagraft is made from human cells placed on a dissolvable mesh material. The mesh material is gradually absorbed and the human cells grow and replace the damaged skin after being placed on the wound or ulcer.
- Biobrane is used as a temporary dressing for a variety of wounds, including ulcers, lacerations, and full-thickness burns. It may also be used on wounds that develop on areas from which healthy skin is transplanted to cover damaged skin. It consists of an ultrathin silicone film and nylon fabric. As the wound heals, or until autografting becomes possible, the Biobrane is trimmed away.
- TransCyte is used as a temporary covering over full thickness and some partial thickness burns until autografting is possible, as well as a temporary covering for some burn wounds that heal without autografting. It consists of human cells from circumcised infant foreskin, and grown on nylon mesh, combined with a synthetic epidermal layer. TransCyte starts with living cells, but these cells die when it is shipped in a frozen state to burn treatment facilities. The product is then thawed and stretched over a burn site. In one to two weeks, the TransCyte starts peeling off, and the surgeon trims it away as it peels.
- Integra Dermal Regeneration Template is used to treat full thickness and some partial thickness burns. Integra consists of two layers; the bottom layer, made of shark cartilage and collagen from cow tendons, acts as a matrix onto which a person's own cells migrate over two to three weeks. A new dermis is created as the cells gradually absorb the cartilage and collagen. The top layer is a protective silicone sheet that is peeled off after several weeks, while the bottom layer is a permanent cover. A very thin layer of the person's own skin is then grafted onto the neo-dermis.
- OrCel is also made from circumcised infant foreskin, grown on a cow collagen matrix, and used to treat donor sites in burn patients. It is also used to help treat epidermolysis bullosa, a rare skin condition in children.
To ensure the safety and quality of products such as cellular wound dressings, the Food and Drug Administration (FDA) has initiated a new regulatory system.
- Hematoma: dressings should be inspected for hemorrhage at intervals during the first 24 hours after surgery. A large amount of bleeding is to be reported to a health care professional immediately. Concealed bleeding sometimes occurs in the wound, beneath the skin. If the clot formed is small, it will be absorbed by the body, but if large, the wound bulges and the clot must be removed for healing to continue.
- Infection: The second most frequent nosocomial (hospital-acquired) infection in hospitals is surgical wound infections with Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Prevention is accomplished with meticulous wound management. Cellulitis is a bacterial infection that spreads into tissue planes; systemic antibiotics are usually prescribed to treat it. If the infection is in an arm or leg, elevation of the limb reduces dependent edema and heat application promotes blood circulation. Abscess is a bacterial infection that is localized and characterized by pus. Treatment consists of surgical drainage or excision with the concurrent administration of antibiotics.
- Dehiscence (disruption of the surgical wound) and evisceration (protrusion of wound contents): This condition results from sutures giving way, infection, distention, or cough. Dehiscence results in pain; the surgeon is called immediately. Prophylactically, an abdominal binder may be utilized.
- Keloid: refers to excessive growth of scar tissue. Careful wound closure, hemostasis, and pressure support are used to ward off this complication.
The goals of wound care include reducing risks that inhibit wound healing, enhancing the healing process, and lowering the incidence of wound infections.
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René A. Jackson, RN Crystal H. Kaczkowski, M. Sc.