Why do wounds and burns cause infection?

Answer 1

Burns are damage to the skin caused by a variety of non-mechanical sources including chemicals, electricity, heat, sunlight or nuclear radiation. Overall burn severity is determined based on the degree of tissue damage and the size of the area affected. Approximately 500,000 burns are treated each year by hospitals across the United States; 40,000 required prolonged hospitalization. Caucasian males are the most likely demographic to sustain a burn injury.

The tissue damage incurred is classified into three categories: first, second and third-degree burns. First-degree burns involve only damage to the topmost layer of the skin, the epidermis. Second-degree burns contain damage to the epidermis as well the dermis, the underlying layer of the skin. Third-degree burns refer to damage or destruction of the entire depth of the skin as well as tissues that lie beneath it. These are three-dimensional injuries with damage extending in all direction from the center of the injury.

The area of a burn is often determined using the "Rule of Nines," which divides the body up into sections that correspond with approximately 9% of the body's surface area. For example, an arm, the abdomen and the entire head each account for 9%. If all three of these body parts were burned, it would be estimated that the patient sustains injuries to 27% of his body. Burn severity is determined by combining information about the source of the burn, the type of damage done and the extent of the body injured. In addition, burn location is important. For example, burns to the face, hands or feet are considered severe because of the resulting complications with airway management, dexterity and movement.

Burns wounds have three separate zones of concern. The zone of coagulation is located where the skin came in contact with the burn source, at the center of the wound. It is made up of dead, leathery tissue that forms the burn eschar (scab). The zone of stasis surrounds the zone of coagulation; tissue is this zone is alive but at a high risk of infection and necrosis (tissue death) due to decreased perfusion, a result of poor circulation, to the area. Lastly, the zone of hyperemia surrounds the zone of stasis and contains healthy skin though vasodilatation in this area is common as a result of the injury. Signs of infection include change in color of the wound, spontaneous separation of the eschar, cellulitis and graft loss. These signs may be accompanied by localized redness, heat and tenderness. Sepsis occurs when microbes or their toxins have expanded past just the wound to infect the rest of the body; this is characterized by high fevers, accelerated heart rate, increased respirations per minute and hyperglycemia.

Infection of burns is common because the skin, a physical barrier against microbes, has been compromised. Furthermore, in moderate and severe burns the underlying vasculature of the skin has been damaged or destroyed and so immunity agents, such as T cells, cannot reach sites of infection. Accordingly, the risk of infection increases proportionately with the size of the burn.