Eschar is a severe wound complication consisting of dead, necrotic tissue firmly attached to the wound surface. This darkened tissue signifies significant damage and tissue death in the underlying skin and potentially deeper layers. Eschar prevents the natural healing process by covering the wound bed and acting as a barrier.
Defining Eschar: Appearance and Composition
Eschar is recognized by its distinctive appearance as a dark brown or black patch of tissue covering a wound. This devitalized layer often has a tough, leathery, and crusty texture, feeling hard and dry. This appearance results from the tissue drying out (desiccation) and the coagulation of proteins and blood components.
Eschar’s composition is primarily non-viable, necrotic tissue, including dried blood, fibrin, and cellular debris. Unlike a simple scab, eschar is a deeply seated product of tissue death, tightly adhered to the surrounding healthy tissue and the underlying wound bed. Occasionally, eschar may present as soft, boggy, or fluctuating, which often suggests an underlying infection beneath the hard outer layer.
Primary Causes of Eschar Formation
Eschar forms when the blood supply to a specific tissue area is severely interrupted, leading to necrosis. While lack of perfusion is the most frequent cause, extreme thermal or chemical damage can also trigger the process. A common cause is a severe, full-thickness burn, such as a third-degree burn, where heat completely destroys the skin and underlying tissue.
Advanced pressure injuries (Stage 3 or Stage 4 ulcers) are another frequent cause, where unrelieved pressure leads to prolonged ischemia. Arterial ulcers also commonly develop black eschar due to chronic poor arterial blood flow, often appearing on the distal toes or malleolus. Chemical burns from strong acids or alkalis can instantly destroy tissue and cause eschar. Eschar can also be a diagnostic sign of certain infectious diseases, such as the site of a tick bite in spotted fevers or in cases of cutaneous anthrax.
Clinical Implications and Risks
The presence of eschar significantly complicates wound management and introduces serious health risks requiring medical intervention. A primary concern is the risk of infection, as the dense, non-living tissue acts as a physical barrier. This barrier prevents immune cells and topical antibiotics from reaching bacteria that proliferate in the warm, moist environment beneath the eschar.
The underlying wound, concealed by the eschar, becomes a breeding ground for bacterial growth, potentially leading to complications like cellulitis or sepsis. A second serious risk arises when eschar forms circumferentially around a limb or the torso, such as after a severe burn. The tough, inelastic nature of the eschar does not stretch, constricting the swelling underlying tissue, vessels, and nerves.
This constriction rapidly compromises blood flow and nerve function, potentially leading to compartment syndrome. In this condition, pressure within the confined tissue compartment rises dangerously high, cutting off circulation and causing further tissue death. To relieve this immediate threat, an emergency surgical procedure called an escharotomy is necessary, involving a deep incision through the eschar to release the pressure.
Management and Removal Methods
The goal of eschar management is to remove the non-viable tissue to expose a clean, healthy wound bed ready for regeneration. This removal process is known as debridement, and the chosen method depends on the wound’s cause, size, depth, and the patient’s overall condition. Surgical debridement, using a scalpel, is the quickest method and is often used for large, deep, or infected wounds, or in emergencies like compartment syndrome.
Enzymatic Debridement
Enzymatic debridement uses topical agents like collagenase to chemically break down necrotic tissue. This process selectively dissolves the dead tissue, allowing it to detach from the healthy tissue underneath.
Autolytic Debridement
Autolytic debridement is a more conservative approach that utilizes the body’s own moisture and enzymes to soften and liquefy the eschar. This technique is supported by specialized moisture-retentive dressings, such as hydrogels or hydrocolloids, which create an optimal environment for the natural breakdown process. While slower, autolytic debridement is highly selective, only affecting the necrotic tissue. Once removed, the wound converts from a necrotic, non-healing state to a viable wound ready to form new granulation tissue and heal.