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.
Three phases of Repair
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.
Four Principles of Wound Care
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. Optimally, Albumin level will be >3.5 g/ml to utilize Negative Pressure Therapy while minimizing the risk of adverse outcome.
Pressure Relief vs Pressure Reduction
Prior to the 1960s there were not any real options available to prevent pressure ulcers. Patients were laid in bed and if they were not turned on a regular basis their skin would break down. If a person were confined to a wheelchair it was almost a given that he/she would develop some kind of pressure related wound. Many devices were used to try and reduce pressures in both the bed and the wheelchair. Some of the more common things used to reduce pressure were sheepskin and goose down pillows; both of these products were very soft, but proved to be ineffective in preventing pressure ulcers.
Interface Pressure is a term used to explain the pressure between two surfaces. In the early 1960's researchers found that in a healthy adult male subject it took an interface pressure of approximately 32 millimeters of Mercury (mmHg) to cause enough pressure on the capillary bed to stop the flow of blood. These same researchers determined that the interface pressure on the same subjects skin when lying on a standard innerspring bed was approximately 80mmHg. Sitting in a wheelchair without a cushion resulted in pressures in excess of 150mmHg. It is these pressures above 32 mmHg that cause the body to naturally turn during sleep and shift its weight while sitting in a chair. Once the pressure on part of the body reaches the point that the mind knows it needs to relieve the pressure to avoid tissue damage the body unconsciously moves into a position that will relieve that pressure. If a person is paralyzed, or his/her cognitive state is such that the mind did not tell the body to move, the results would be tissue damage.
As a result of these studies the terms Pressure Reduction and Pressure Relief were born. The term Pressure Reduction refers to any surface that provides pressures less than those pressures found on a standard innerspring mattress, so something less than 80mmHg but more than 32mmHg worth of pressure. Pressure Relief refers to any surface that provides pressures that are consistently at or below 32mmHg.
Patients that are at risk of developing pressure ulcers but have good cognitive skills and are not paralyzed can be placed on a Pressure Reduction mattress or have a Pressure Reduction wheelchair cushion placed in his/her wheelchair that will adequately prevent the formation of a pressure ulcer. For people that already have a pressure ulcer, are cognitively impaired, or are paralyzed a Pressure Relief device is generally used to prevent further tissue damage or the development of pressure ulcers.
However, in 2007 the National Pressure Ulcer Advisory Panel determined that the term Pressure Redistribution would replace both terms. Due to the terms "Relief" and "Reduction" being confused and misused.