Types of burns

Thermal burns can occur as a result of exposure to various external heat sources (flames, liquids, solid objects, and gases). Fire can also cause inhalation of toxic combustion products.

Radiation burns are most common after prolonged exposure to the sun's ultraviolet radiation (sunburn) or after prolonged or intense exposure to other sources (eg, tanning beds), as well as after X-rays or non-solar radiation.

Chemical burns are the result of exposure to concentrated acids or alkalis (e.g. lye, cement), phenols, cresols, mustard gas or phosphorus. Necrosis of the skin and underlying tissues as a result of this exposure can develop within a few hours.

Burns of the respiratory tract and smoke inhalation often occur simultaneously, but can also occur separately. When smoke is inhaled, toxic combustion products and, in some cases, high temperatures damage the tissues of the respiratory tract. High temperatures usually affect only the upper respiratory tract, since the full heat load of the incoming gas in most cases reaches only the upper respiratory tract. An exception is steam, which often burns the lower respiratory tract as well. Many toxic chemicals formed during normal household combustion (e.g., hydrogen chloride, phosgene, sulfur dioxide, toxic aldehydes, ammonium) irritate and damage the lower and sometimes the upper respiratory tract. Some toxic combustion products, usually carbon monoxide and cyanides, damage cellular respiration throughout the body.

Upper airway symptoms usually develop within minutes but may take several hours; upper airway swelling may cause stridor. Lower airway symptoms (shortness of breath, wheezing, and sometimes cough and chest pain) usually develop within 24 hours.

Smoke inhalation should be suspected in patients with respiratory symptoms, prolonged exposure to a scalding environment, and sooty sputum. Burns around the mouth and singed nasal hairs may also suggest this diagnosis unless caused by a flare-up of an open flame (eg, from a barbecue grill). The diagnosis of upper respiratory tract involvement is based on endoscopic examination (laryngoscopy and bronchoscopy), which is sufficient to fully examine the upper respiratory tract and trachea and may reveal swelling and soot in the airways. However, in some cases, the endoscopic appearance is normal in the early stages, and the lesion develops later. Endoscopy is performed as soon as possible, usually with a flexible endoscope. The diagnosis of lower respiratory tract involvement is based on chest radiography, oximetry, or blood gas measurements; the diagnosis may not be confirmed for up to 24 hours.

All patients with suspected inhalation injury are given 100% O2 via facemask until the diagnosis is confirmed. Patients with airway obstruction or respiratory failure require endotracheal intubation or other form of airway protection and mechanical ventilation. Patients with edema and significant carbonization of the upper airway should be intubated as soon as possible, as this becomes more difficult as edema increases. Patients with lower airway injury may require masked O2, bronchodilators, and other supportive measures.

Electrical burns are the result of tissue exposure to heat generated by electricity; it can cause extensive deep tissue damage with minimal skin changes.

Incidents that involve burns (such as jumping from a burning building, being trapped under rubble, or being in a car accident) can also result in other injuries.

Burns cause protein denaturation and coagulative necrosis. Platelet aggregation, vasospasm, and a critically reduced blood supply (called the stasis zone) around the coagulated, burned tissue may also cause necrosis. The tissues around the stasis zone are hyperemic and inflamed. Damage to the normal epidermal barrier allows bacterial invasion and extrinsic fluid loss. Damaged tissues often swell, leading to further fluid loss. Due to epidermal damage, thermoregulation is impaired, fluid leakage increases evaporative heat loss, which together significantly increases heat loss.

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