Factors affecting healing

A number of local and systemic factors affect wound healing (Table 3.1); these are discussed in turn.

Local factors

Wound sepsis

Removal of hair allows better visualisation of the wound. It also facilitates application of adhesive dressings and suture removal. However, evidence has shown that shaving of skin at an early stage preoperatively increases bacterial counts in the area, and shaving more than 12 h before incision can significantly increase the rate of wound infection. Hair removal should therefore be performed where necessary just prior to surgery (see Ch. 8).

Preparing the skin with antiseptic wash prior to surgery is vitally important. Preparation should be thorough. Chlorhexidine and povidone-iodine have been shown to reduce the skin bacterial flora by up to 95%. Most surgeons perform a double scrub of the area, preparing

Table 3,1 Factors affecting wound healing

Local wound sepsis poor blood supply wound tension foreign bodies previous irradiation poor technique Systemic nutritional deficiencies systemic diseases therapeutic agents age the skin well wide of the area of surgery. Careful hand wash by the surgeon using these antiseptics is also very important in reducing wound sepsis.

Poor blood supply

As described above, bleeding and neovascularisation play fundamental roles in wound healing. Areas with good vascularity, such as the scalp and face, heal well, whereas those with poor blood supply, such as pretibial skin, heal poorly. Surgical technique can also have a significant effect on the blood supply to the area. Care should be taken where possible to maintain the vascular supply to the incised area. For example, creation of a distally based skin flap is likely to disrupt the vessels to the skin of the flap, and impair wound healing. Appropriate planning of incisions minimises vascular damage.

Wound tension

Tension across a healing wound serves to separate the wound edges, impairs the blood supply to the area and predisposes to complications of wound healing. Care should be taken, therefore, when planning incisions to avoid creating tension if possible.

Where the gap between the wound edges is large, primary apposition of the edges might not be appropriate or even possible. Bridging of such a gap can be achieved by a number of plastic surgery techniques, including skin grafting or tissue flaps (see Ch. 15).

Better cosmetic results from surgery tend to be achieved if incisions are made along the lines of the collagen bundles of the skin (Langer's lines). These follow the natural skin creases on the face, transversely at the joints and longitudinally on the long parts of the limbs.

Foreign bodies

The presence of extraneous material within the wound predisposes to infection. It also results in a larger and more prolonged inflammatory reaction, which can predispose to excess scar tissue formation. Foreign material can enter a traumatic wound at the time of injury and should be removed at the onset of treatment with adequate debridement.

With surgical wounds, however, complications can result from endogenous material being inappropriately present within the wound, such as devascularised pieces of fat, necrotic tissue resulting from excess use of the diathermy, or the patient's hair. Thorough wound cleaning before closure helps to remove these materials.

Previous irradiation

Areas that have undergone preoperative radiotherapy suffer from a patchy vasculitis, impairing their blood supply and hence healing potential. Radiation also damages skin stem cells, resulting in poor re-epithelialisation.

Poor technique

Care should be taken when making an incision to create a clean precise cut. The incision should be made vertically through the skin. Gentle handling of tissues throughout the operation is important. Rough handling and damaging of tissues can result in tissue edge necrosis, predisposing to poor healing and infection. Careful haemostasis not only allows good visualisation during surgery but also reduces tissue bruising and haematoma formation.

Choice of appropriate suture material is important. Suture placement should be precise and suture tension sufficient to result in tissue apposition, but not too tight to cause tissue necrosis. Skin closure should include the strength-supplying dermis within the bite. Removal of sutures at the correct time (variable between sites) helps prevent scarring associated with the sutures themselves.

Systemic factors

Many systemic factors are necessary for wound healing and deficiency of these impairs the process. Certain diseases and therapies can also have detrimental effects on the wound.

Nutritional deficiencies

Vitamins important in the process of wound healing include A and C. Vitamin A is involved in epithelialisation and collagen production; vitamin C has an important role in the production and modification of collagen. This has been recognised for centuries by virtue of the disease scurvy caused by vitamin C deficiency.

Certain minerals are also essential in wound healing. Zinc acts as an enzyme cofactor and has a role in cell proliferation. It accelerates wound healing in experimental models. Deficiency may be encountered in patients on long-term total parenteral nutrition.

Protein is the main building block in wound healing. A malnourished, hypoproteinaemic patient has impaired inflammatory and immune responses, vital for normal wound healing and prevention of wound infection. Protein amino acids are essential for collagen production, which is itself a protein.

Systemic diseases

Several diseases are known to impair wound healing via a number of mechanisms. Important examples include diabetes, uraemia and jaundice.

Therapeutic agents

Immunosuppressive drugs dampen the inflammatory and immune responses, hence impairing wound healing. These include chemotherapeutic agents for malignancy and immunosuppressive and antiprostaglandin drugs used for inflammatory conditions such as rheumatoid disease. Probably the most important and widely used example is corticosteroid therapy. Steroids have the additional effect of increasing the fragility of small blood vessels.

Prior to puberty, the rate of wound healing is increased compared to postpuberty.

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