Burn Injury

Burns are injuries that occur when the skin and underlying tissues are damaged from exposure to heat, chemicals, electricity, or radiation. Burns can cause localized damage or have widespread effects that can impact multiple organs in the body.

Okay, the skin is the largest organ in the body and provides important body functions like helping regulate body temperature, preventing loss of body fluids, and protecting against microorganisms, radiation, and mechanical stress.

Now, the skin is comprised of two main layers, the epidermis and dermis, that rest upon the hypodermis, that’s sometimes considered a third layer of the skin. The epidermis, or the outermost layer, is composed of multiple layers of keratinocytes, that synthesize keratin, a protein that forms a tough, waterproof barrier to shield underlying structures from mechanical stress. The epidermis also contains melanocytes, which produce melanin, a pigment that helps protect the skin from ultraviolet radiation.

The next layer is the dermis, which contains structures like hair follicles, nerves, sensory receptors, and sweat glands. This layer also contains macrophages and mast cells that aid in immune function. Lastly, the hypodermis is the subcutaneous layer, made up of fat and connective tissue that insulates deeper tissues and anchors the skin to the underlying muscle.

Now, burn injuries can be classified as thermal or non-thermal. Thermal burns result from direct contact with a hot object, open flame, hot liquid, or steam. Other causes of thermal burns include electrical shock and friction. On the other hand, non-thermal burns come from a source other than heat. For example, chemical burns occur from exposure to strong acids, alkalis, or solvents, either by direct contact with the skin, inhalation into the respiratory tract, or ingestion into the GI tract. Non-thermal burns can also be caused by ultraviolet light and radioactive sources.

Most burns occur in the home; and individuals at highest risk for burn injuries include biological males, those who are younger than age 4 or older than 65, and individuals who are economically challenged or live in substandard housing.

Local effects of a burn injury can be described in three zones. First, the zone of necrosis is the central zone where the heat transfer is greatest, resulting in coagulative necrosis and irreversible cell death. Surrounding this is the zone of stasis, where damage to the microcirculation results in sluggish circulation. This zone is potentially salvageable with appropriate treatment. Lastly, the outermost area is the zone of hyperemia, characterized by vasodilation, increased blood flow, and limited cellular damage that can heal on its own.

As far as systemic effects of burn injuries go, cellular damage causes the release of inflammatory mediators, and the resulting inflammatory response causes increased capillary permeability and vasodilation.

As capillary permeability increases, third spacing occurs as plasma proteins move out into the interstitial space, pulling fluid with them. This leads to an accumulation of fluid within the interstitial space and a decreased intravascular volume. This, together with lost fluid through evaporation from the burned surface, further decreases circulating volume, resulting in hypotension.