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The repair of damaged cells and tissue takes place by regeneration, in which structures are replaced by proliferation of similar cells, such as happens with skin and bone; and by formation of a scar, consisting of fibrous structures with some degree of contraction. Since most wounds extend to more than one type of tissue, complete regeneration is impossible; therefore, scar formation is an expected outcome of wound healing.
In healing by first intention (primary union), restoration of tissue continuity occurs directly, without granulation; in healing by second intention (secondary union), wound repair following tissue loss (as in ulceration) is accomplished by closure of the wound with granulation tissue. This tissue is formed by proliferation of fibroblasts and extensive capillary budding at the outer edges and base of the wound cavity, with slow extension from the base and sides of the wound toward its center. If, however, the wound is very deep and extensive, granulation tissue cannot fill the defect and grafting may be needed to cover the space and avoid severe contracture and loss of function. healing by third intention (delayed primary closure) occurs when a wound is initially too contaminated to close and is closed surgically 4 or 5 days after the injury. (See also illustrations at healing.)
The insertion of drains can facilitate healing by providing an outlet for removing accumulations of serosanguineous fluid and purulent material, and obliterating dead space such as that created by surgical removal of an organ.
If the area of injury is not very large, the products of inflammation, small blood clots, and other debris from the wound can be absorbed into the blood stream and disposed of. Wounds that are filled with large amounts of dead cells, blood clots, and other debris must be cleansed in order for healing to take place. This can be accomplished by surgical or chemical débridement or by irrigations. Enzymes are sometimes used to remove the debris by enzymatic action. Since foreign bodies, such as sutures, slivers of glass, splinters, and the like, can delay healing, they too must be removed from the wound to facilitate healing.
Dressings also must be observed frequently, especially a pressure dressing, which can become dangerously restrictive if there is swelling. Any change in sensation, such as tingling or numbness, signs of impaired circulation, or complaint of discomfort, should be reported to the physician.
Other data important to the ongoing assessment of wound healing are the leukocyte count, coagulation tests, and electrolyte levels. An elevated body temperature can signal local or systemic infection. Another sign of infection is the presence of purulent drainage. The color of the drainage is often indicative of the particular infecting organism. For example, a yellow color may indicate presence of Staphylococcus aureus, and a blue-green color may indicate Pseudomonas aeruginosa infection.
In a surgical wound, a discharge of serosanguineous fluid on the fourth or fifth postoperative day may signal wound dehiscence and, therefore, should be reported immediately to the surgeon.
During the scarring phase of healing, the wound is inspected for changes in size, color, and shape, which can continue for months even in superficial wounds. New scar tissue is usually purplish, raised, and irregular. With time, the color fades, the scar grows smaller, and its surface and edges become less irregular. Sometimes the scar tissue grows to excess and extends beyond the normal limits of the wound. This hypertrophic scar or keloid may require steroid injections or surgical removal.
In order to achieve adequate and uneventful healing of a wound the patient must be in a good state of nutrition. Virtually every nutrient plays some role in the healing process; hence, a wide range of dietary nutrients must be supplied, either through oral feedings, supplemental vitamins and protein, or parenteral nutrition. Oxygen is also essential to the healing process. This means that measures must be taken to ensure adequate circulation of blood to the wound, employing measures such as exercise, ambulation when possible, and applications of warmth when prescribed. Positioning also is important to avoid prolonged pressure against blood vessels serving the wounded area. Adequate rest is needed to facilitate healing. The patient should understand the need for rest and the purpose of splints, casts, and other devices employed for immobilization of a wounded part.
Mechanical injury to a wound can greatly impede healing by damaging the tissues involved in the healing process. The wound should be protected from friction and direct blows. The affected part must be handled gently, and great care must be used in applying and removing dressings and bandages. Protective bandages and shields made from rubber, plastic cups, tongue blades, and other supportive materials may be needed to protect the wound from additional trauma.
Other factors that work against optimal healing are stress, old age, smoking, obesity, and diabetes mellitus. It is thought that in the poorly controlled diabetic patient there is an increased affinity of hemoglobin for oxygen, which hampers the release of oxygen to the healing tissues. Additionally, poorly controlled diabetic patients have an abnormal function of the phagocytes, which predisposes wounds to infection. Although cancer does not itself interfere with the healing process or make the patient more susceptible to infection, radiation therapy, steroids, and antineoplastic agents, as well as the general debility of the patient, do compromise healing in cancer patients.
wound healingPhysiology The repair of a wound Steps Inflammation, repair and closure, remodeling, final healing; repair of incisions may be either simple–'clean' wounds with little loss of tissue heal by 'primary intention', or 'dirty' wounds heal by 'secondary intention'
Patient discussion about wound healing
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