Wound classification provides a framework for healthcare professionals to describe injuries. This standardized method is for selecting appropriate treatments and predicting healing outcomes, and it ensures clear communication among clinical teams. This approach leads to more effective and coordinated patient care.
Classification by Cause and Duration
A distinction is made between acute and chronic wounds. Acute wounds progress through the normal stages of healing in a predictable and timely manner, whereas chronic wounds fail to do so, often stalling in the inflammatory stage.
Surgical wounds are a type of acute wound, created in a sterile environment and closed with sutures or staples. Traumatic wounds result from accidental injury and include lacerations, which are cuts through the skin, and abrasions, where the skin is scraped away. Skin tears are a specific type of traumatic wound common in older adults, where the fragile layers of the skin separate.
Chronic wounds often develop from an underlying medical condition that impairs the body’s natural healing capabilities. Arterial ulcers are caused by poor arterial blood flow, leading to tissue damage, often on the feet and toes. Venous ulcers are more common and result from dysfunctional veins that cause blood to pool in the lower legs, increasing pressure and breaking down the skin.
Diabetic, or neuropathic, ulcers are a frequent complication of diabetes. Nerve damage, known as neuropathy, reduces sensation, making a person unaware of minor injuries, while compromised blood flow hinders healing. Pressure injuries, also called pressure ulcers, occur when prolonged pressure on the skin, usually over a bony prominence, cuts off blood supply, leading to tissue death.
Classification by Tissue Involvement and Depth
A method for describing wound severity involves assessing the depth of tissue damage, which is formally applied in the staging system for pressure injuries. This system allows clinicians to categorize wounds based on the anatomical layers affected, from superficial skin changes to extensive tissue loss.
The staging system begins with Stage 1, characterized by intact skin with a localized area of non-blanchable erythema, meaning the redness does not fade when pressed. Stage 2 involves partial-thickness skin loss, where the wound bed is viable, pink or red, and moist; it may present as an intact or ruptured serum-filled blister. The epidermis and part of the dermis are involved.
A Stage 3 pressure injury signifies full-thickness skin loss. In this stage, the wound extends through the dermis into the subcutaneous tissue, and adipose (fat) is often visible. Granulation tissue and epibole are often present. Slough or eschar, types of dead tissue, may also be visible.
Stage 4 injuries involve full-thickness skin and tissue loss, with exposed or palpable fascia, muscle, tendon, ligament, cartilage, or bone. Slough and eschar are commonly present, and undermining or tunneling often occurs. The depth of a Stage 4 injury varies by anatomical location.
An Unstageable pressure injury is characterized by full-thickness skin and tissue loss in which the extent of damage cannot be confirmed because it is obscured by slough or eschar. A Deep Tissue Pressure Injury (DTPI) presents as a persistent, non-blanchable deep red, maroon, or purple discoloration of intact or non-intact skin.
Classification by Contamination and Infection Risk
Surgical wounds are classified by their level of microbial contamination to predict the risk of a surgical site infection. This system informs clinical practice, including decisions about antibiotic use and the method of wound closure. It separates wounds into four classes:
- Class I (Clean): Uninfected wounds with no inflammation that are primarily closed. They do not involve entering the respiratory, gastrointestinal, genital, or uninfected urinary tracts, and the infection risk is minimal.
- Class II (Clean-Contaminated): Wounds that involve entry into the respiratory, alimentary, genital, or urinary tracts, but under controlled conditions and without unusual contamination or evidence of infection.
- Class III (Contaminated): Open, fresh, accidental wounds, or surgeries with a major break in sterile technique, such as gross spillage from the gastrointestinal tract. Incisions with acute, non-purulent inflammation also fall into this category.
- Class IV (Dirty-Infected): Old traumatic injuries with retained devitalized tissue and those that involve existing clinical infection or perforated viscera. These wounds have the highest risk of surgical site infection.
The Red-Yellow-Black System for Wound Bed Assessment
A visual system used for managing wounds is the Red-Yellow-Black classification. This method helps guide treatment by focusing on the appearance of the wound bed itself, allowing clinicians to determine the most immediate need for care. It is a dynamic assessment, as the appearance of a wound can change as it heals or deteriorates.
Red in the wound bed signifies the presence of healthy granulation tissue, which is the foundation for healing. The primary goal for a red wound is to protect this new tissue and maintain a moist environment to encourage continued growth and epithelialization. Treatment involves gentle cleansing and the use of dressings that prevent the wound from drying out.
A wound with a yellow appearance indicates the presence of slough, which is non-viable, moist, stringy tissue that adheres to the wound bed. This material must be removed for the wound to heal properly. The treatment goal for a yellow wound is cleansing to remove the slough and absorb any excess drainage.
Black coloration indicates the presence of eschar, which is thick, dry, necrotic tissue. Eschar is a barrier to healing and must be removed through a process called debridement. A single wound can display all three colors, and in such cases, treatment addresses the most severe impediment first: black, then yellow, and finally red.