The Wound Healing Process
Promoting the wound healing process is a primary responsibility for most health care practitioners. It can take 1-3 days for a closed wound to actually establish a seal. Infections usually occur in 3-6 days but may not appear for up to 30 days, according to the CDC guidelines for preventing surgical infections. The wound healing process can be seen as an overlapping healing continuum, which can be divided into four primary phases:
The hemostasis phase of the wound healing process begins at the moment of the initial injury, and takes approximately 15 minutes. Whether a surgical incision or accidental breakage of the skin, a wound starts an outflow of blood and lymphatic fluid. This starts the hemostasis phase of the wound healing process, which aims to stop the bleeding. During this process, platelets adhere to the damaged endothelium and discharge ADP (adenosine diphosphate) to create clumping in the thrombocytes, which stops up the wound. The enzyme thrombin initiates the creation of a fibrin mesh, which stabilizes the platelets into a stable clot. After the vasoconstriction is finished, the blood vessels dilate to allow an influx of other blood cells and thrombocytes.
The inflammatory response is the defensive phase of the wound healing process that lasts 4-6 days, and is often associated with swelling of tissues, reddening of the skin around the wound, heat, and pain. This stage of the wound healing process focuses on removing debris and destroying bacteria. Within 24-48 hours after the initial injury, white blood cells called neutrophils reach their peak population, and do their work of killing bacteria and taking away debris. As the neutrophils leave after about three days, specialized macrophages enter the wound site and continue the debris cleanup. Macrophages secrete proteins that orchestrate:
- The multiplication of endothelial cells
- Sprouting of new blood vessels
- Duplication of smooth muscle cells
Macrophages also secrete growth factors like TGFs, cytokines, interleukin-1, tumor necrosis factor, and PDGF, which attract immune system cells and begin tissue repair.
Now that the wound is clean, the proliferative phase (which lasts 4-24 days) begins the process of filling and covering the wound with new skin. This phase of the wound healing process has 3 stages that operate in an overall and ongoing process:
1. Filling the wound
2. Contracting the wound margin
3. Growing new skin over the wound or re-epithelialization
First, red granulation tissues fill the wound bed with connective tissues and new blood vessels. Next, in contraction, the margins of the wound begin to pull to the center of the wound to close it up. Finally, epithelial cells come up from the wound bed and margins, and migrate until the whole wound is covered with new skin or epithelium.
The remodeling (or maturation) phase of the wound healing process is where the wound bed slowly strengthens and gains flexibility. The collagen fibers reorganize, remodel, mature, and regain the tensile strength of up to 80% pre-injury. The collagen deposit in normal wound healing reaches a peak in the 3rd week, and maximal tensile strength is usually achieved by the 12th week. Depending on the severity and type of wound, the remodeling stage can last from 21 days to 2 years.
Primary Intention Wound Healing Process
Primary wound healing occurs when the tissue surfaces are closed by stitches, staples, skin glue, or steri-strips. A surgical incision that is closed by stitches is a good example. This sort of closure of the wound surfaces creates very little tissue loss, and makes the wound healing process as quick and easy as possible.
Secondary Intention Wound Healing Process
Secondary intention happens when a wound has a great deal of lost tissue, or is extensive and the edges can't be brought together. An example would be a pressure ulcer. The wound healing process for secondary intention is different from primary intention in three ways:
- Longer repair and healing time
- Greater chances of scarring
- Increased chance of infections
Tertiary Intention Wound Healing Process
A tertiary intention, also called delayed or secondary closure, occurs when there is a need to delay closing a wound, such as when there is poor circulation in the wound area or infection. An example would be an abdominal wound that is kept open in order to allow drainage, and then later closed. This type of wound healing process creates more connective scar tissue than other intentions.
Health practitioners need to keep the four stages of the wound healing process in mind, and remember that the type of wound intention influences the time the process takes.
The views and opinions expressed in this blog are solely those of the author, and do not represent the views of WoundSource, Kestrel Health Information, Inc., its affiliates, or subsidiary companies.