What is that yellowish-white membrane inside the wound?

When changing dressings, a thin, pale yellow or grayish-white film is often seen covering the wound surface. It is moist and soft, and may slightly slide when touched with a cotton swab, but there is no obvious purulent discharge. Many people mistake this film for pus or necrotic tissue and try to remove it completely by vigorously wiping it with gauze soaked in saline solution. This only worsens the bleeding, and the film reappears at the next dressing change, sometimes even covering a larger area. This film, known as a biofilm in wound care, is a fibrin aggregate formed when fibrinogen from exudate seeps into the wound and is converted into fibrin aggregates by thrombin. It intertwines with the newly formed capillaries and fibroblasts at the wound base, forming a temporary protective matrix. The value of this matrix lies in providing a scaffold for cell migration and a storage site for growth factors for subsequent granulation tissue growth, while also covering exposed nerve endings to reduce pain.

Is the appearance of a yellowish-brown dura mater at the base of the wound a good or bad sign? 

Unlike the aforementioned soft membrane, some chronic wounds develop a dry, yellowish-brown or grayish-brown dura mater during the stagnant healing phase. This mater adheres tightly to the wound base, is difficult to remove with forceps, and bleeds easily. This dura mater differs from fresh fibrin membranes; it is a fibrin scab formed after long-term dehydration and concentration of exudate, containing inactive leukocytes, bacterial metabolites, and necrotic tissue fragments. Its presence indicates a chronic inflammatory state, with a low-level pathological balance between exudate production and evaporation. The wound is sealed by this necrotic protein layer, preventing granulation tissue from growing from the base and epithelial cells from spreading inwards. This condition requires professional debridement to remove the necrotic fibrin scab before the wound can re-enter the healing cycle. At home, attempting to tear off this dura mater can easily cause deep tissue damage and bleeding. Treatment should be performed at a wound clinic by medical professionals after assessment, using methods such as autolytic debridement, enzymatic debridement, or mechanical debridement. After debridement, a healthy, moist wound environment can be re-established, allowing granulation tissue to grow on a clean base. 

What kind of tissue is truly necrotic tissue that needs to be removed ?

The tissue at the base of a wound can be classified according to its activity and color. This classification system provides a clear reference for determining whether debridement is necessary. Black tissue is dry eschar, composed of dehydrated and necrotic full-thickness skin and subcutaneous tissue. It is hard like leather, has completely lost its blood supply and activity, and must be removed. Yellow tissue is moist necrotic slough, composed of liquefied necrotic fat, collagen fragments, and large clumps of bacteria. It is soft and can be easily separated with tweezers, but may leave irregular wounds. It is also a clear target for debridement. Red tissue is healthy granulation tissue with a fine granular surface. It bleeds easily when touched and is bright red like fresh beef. It is repair tissue that absolutely cannot be removed. When changing dressings, the rinsing should be done gently to avoid damaging the granulation particles. Pink tissue is the epithelialized area, usually appearing at the wound edge as a translucent pinkish-white membrane that creeps from the edge towards the center. It indicates that epidermal cells are covering the wound surface and is a sign that healing is nearing completion. It should not be disturbed. The processing strategies corresponding to the four colors are clear, clear, protect, protect, that is, black and yellow for clearing, and red and pink for protecting. This four-color rule can serve as the basic framework for determining the direction of operation each time the medicine is changed. 

In which situations should we be wary?

The healthy, rosy color of granulation tissue comes from a rich network of newly formed capillaries. If the color of the granulation tissue gradually changes from bright red to dark red or even dark purple, accompanied by increased swelling and pain, it may indicate obstructed venous return or deep infection leading to microcirculatory disturbances. Pale granulation tissue, resembling anemia, with little or no bleeding upon light touch, suggests insufficient blood supply to the local tissue, commonly seen in ischemic arterial diseases or wounds with prolonged pressure. This type of ischemic granulation tissue lacks healing ability, and the wound may continue to expand or stagnate. Another type is gray granulation tissue, with a thin layer of grayish-white secretions on the surface, a loose and edematous texture, and a noticeable indentation when lightly pressed with a finger. This indicates infection or severe malnutrition, requiring a change of antibacterial dressing and an assessment of the patient's overall nutritional status. Of these three abnormal colors, the lighter and whiter the granulation tissue, the more ischemic it is; the darker and purpler it is, the more congested or deeply infected it is. In all cases, the cause needs to be identified and treated accordingly, rather than repeatedly changing dressings of different brands on the wound.

How should tissues of different colors be treated separately in the same wound? 

In clinical practice, wounds rarely contain only a single color of tissue. Typically, black eschar, yellow slough, and red granulation tissue are distributed simultaneously within a single wound surface, with possible pinkish epithelialized bands at the edges. The treatment principle is to treat the wound according to the most severe tissue type, prioritizing the removal of black eschar and yellow slough, as these necrotic tissues not only provide a culture medium for bacteria but also release inflammatory factors that hinder the growth of surrounding healthy granulation tissue. The choice of debridement method is determined based on a comprehensive assessment of the wound location, the patient's pain tolerance, and coagulation status. Sharp instrument debridement is fast but requires specialized operation. Autolytic debridement, using hydrocolloid or hydrogel dressings to seal and soften necrotic tissue, is gentler but time-consuming and suitable for patients who cannot tolerate sharp instrument debridement. After necrotic tissue removal, the wound area is usually visually larger than before debridement. This is not due to wound deterioration but rather the exposure of the actual defect previously hidden under the eschar and slough. Granulation tissue will then gradually fill the defect from this clean base. The zoned treatment method is suitable for home settings where the four colors of tissue have been clearly identified. For complex wounds with mixed colors that are difficult to distinguish, it is best to have a professional debridement performed at a wound clinic to establish a clear base. Subsequent home care only requires maintaining a moist healing environment on the pink base, significantly reducing the difficulty of judgment and operation. Accurately identifying the four colors of tissue provides a basis for determining what to leave and what to remove during wound dressing changes, which is far more accurate and safer than blindly scrubbing. For more information on Innomed® Silicone Foam Dressing, refer to the Previous Articles. If you have customized needs, you are welcome to contact us; You Wholeheartedly. At long-term medical, we transform this data by innovating and developing products that make life easier for those who need loving care.

Editor: kiki Jia