Anatomy and pathophysiology of the burn wound

The burn wound is divided anatomically into a partial versus full thickness wound based on the depth of burn (Figure 11.1). Partial thickness burns are further divided into two subtypes: partial thickness and deep burns.

Figure 11.1 Burn wound depth: 1) superficial partial thickness burn; 2) Deep partial thickness burn (superficial tissues injured); 3) Full thickness burn (all tissues injured beyond repair) (Wolf and Herndon, 1999, Vademecum in Burn Care. Austin, Texas: Landes Bioscience).

The anatomical terms widely used are described below:

1 1st degree burns: Only involves the epidermis and is erythematous and painful in nature. There is usually blistering. The wound blanches under pressure, and sensation is usually intact.

2 2nd degree burns: Involves the entire epidermis and the upper portions of the dermis. It is also painful as well. There is some blistering. The wound could be moist or dry. There is no blanching, and sensation is diminished.

3 3rd degree burns: Involves the epidermis, the dermis, and all adnexal structures. There is no blistering. It is leathery-like in nature and feels hard to touch. There is charring, and the wound is dry and painless.

As mentioned previously, the partial burns can further be divided into superficial and deep-based on adnexal involvement. They are superficial if most adnexal structures are intact, that is if there is sparing of a significant amount of hair follicles and glands (sebaceous and sweat) and also if a minimum proportion of the dermis is involved. It is deemed deep when only deep adnexal structures are intact. In this case, there is an enormous amount of hair follicles, glands, and a substantial amount of dermis destroyed.

Histologically, the burn wound is classified into three zones deferentially:

1 Zone of coagulation: This is the central zone of tissue necrosis, also referred to as the zone of necrosis. Some of the prominent features include but are not limited to denatured proteins, coagulated blood vessels, increase in intracellular sodium as a result of falling sodium-potassium pump, a significant increase in free radicals with subsequent damage to the cell membrane, and finally protein denaturation.

subcutaneous tissue epidermis dermis subcutaneous tissue epidermis dermis

zone of coagulation zone of hyperemia zone of stasis

Figure 11.2 Burn wound classification in zones. 1) Zone of coagulation; 2) zone of stasis; 3) zone of hyperemia (Modified from Herndon, 2001, Total Burn Care. Sidcup, Kent: Harcourt International).

zone of coagulation zone of hyperemia zone of stasis

Figure 11.2 Burn wound classification in zones. 1) Zone of coagulation; 2) zone of stasis; 3) zone of hyperemia (Modified from Herndon, 2001, Total Burn Care. Sidcup, Kent: Harcourt International).

2 Zone of stasis: This zone surrounds the central area of the necrosis zone of coagulation. In this zone, there is impaired circulation. It is also known as the zone of ischemia. Tissue in this area can heal without any complication, or the lesion can progress and lead to a greater depth of injury. This zone of ischemia is as a result of thermal injury to the red blood corpuscles rendering them inflexible and unable to enter the microvasculature. Edema occurs over time, as a result. There is an influx of inflammatory mediators including histamine, prostaglandin E (PGE), prostaglan-din I (PGI), prostaglandin F2 (PGF2), interferon, interleukin-1, interleukin-2, monocyte/macrophages, free radicals, tumor necrosis factor, thromboxane A2 (TXA2), transforming growth factor^, platelet-derived growth factora, PDGp, and platelets. This zone is of utmost importance in the initial management of burn wounds.

3 Zone of hyperemia: Also know as the zone of inflammation. It surrounds the zone of stasis. Vascular permeability is pronounced in this zone with subsequent edema formation, which if left unattended can lead to hypovolemic shock. This zone generally recovers promptly (Figure 11.2).

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