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Assessing Wound Drainage in Acute and Chronic Wounds

Wound drainage, also known as exudate, is a natural and beneficial component of the healing process. However, chronic wound exudate differs in composition from that of acute wounds and impedes wound healing. This article assesses the various types of drainage and offer exudate management procedures to aid optimal wound healing. 

What is Wound Drainage?

Wound drainage is a fluid produced from the blood vessels during the inflammatory phase of healing, which is similar to blood plasma. Exudate consists of a mixture of water, proteins, white blood cells, inflammatory mediators, and electrolytes, which play essential roles in wound healing. For example, white blood cells or leukocytes help to kill off pathogenic microorganisms responsible for wound infections, help clean the wound and stimulate collagen production. Exudate also provides nutrients and serves as a medium for migration and cellular division of epithelial cells. 


Clinical research shows that drainage in acute wounds provides a moist environment ideal for optimal healing. Contrarily, due to its highly alkaline nature, chronic wound exudate needs to be removed from the wound bed regularly. Research has shown that acidic microenvironments activate inflammatory programs in fibroblasts that induce tissue remodeling. Also, excess exudate in-situ for long periods can result in moisture-associated skin damage that may compromise the integrity of peri-wound skin. 

Types of Wound Drainage

Every wound care professional needs to be able to distinguish between the various types of exudate to determine the condition of wounds and administer appropriate care. Wound drainage can be identified in terms of the color, consistency, amount, and the presence or absence of foul odor. The main types of drainage are outlined below:

Sanguineous

Sanguineous wound exudate is composed of blood and viscous serum and does not signal the presence of localized or systemic infection. It usually occurs in a healthy wound after the initial skin breach due to trauma or surgery. The color of drainage is typically bright red or pink with a thickness and consistency similar to syrup. In full-thickness or deep partial-thickness wounds, sanguineous exudate occurs for a few days after an injury and decreases rapidly. However, drainage that is excessive or persists after this period is indicative of delayed healing. 

Serous

Serous wound exudate is light and clear and consists of serosal (serous) fluid. It is frequently observed in venous insufficiency ulcers and partial-thickness wounds and does not give off a pungent odor. Serous drainage is considered beneficial as it comprises proteins, sugars, leucocytes, and others that facilitate healing processes. This type of exudate is produced during the inflammatory stage (during the first 48 to 72 hours), which is perfectly normal. However, an increasing volume of exudate that soaks a wound dressing several times a day can be indicative of a high bioburden and should be observed more closely for signs of edema or the presence of bacterial infection in the wound. 

Seropurulent

Seropurulent wound drainage appears as a light, green, brown, yellow, or tan fluid and is often indicative of a developing or clearing infection. Note that the exudate color alone is not sufficient to determine the presence of an infection. However, any obvious divergence from clear drainage should be examined closely. 

Purulent

Purulent wound drainage, also called "pus" is a milky, malodorous fluid yellow, green, grey, or tan in color. Purulent exudate is composed of debris, white blood cells, and dead bacteria, and is almost always a sign of wound infection. The presence of purulent exudate is associated with impaired healing and usually increases as the wound progresses. Apart from the bad odor of purulent drainage, wound tissues may also become painful and swollen. Some risk factors that contribute to infection in chronic wounds include diabetes, obesity, immunodeficiency, and smoking.