The process of wound healing is complex in which the skin and the tissues beneath it repair themselves after an injury. Wound healing is explained in different phases consisting of the post-trauma repairing procedure. The outer layer (epidermis) and deeper layer (dermis) creates a barrier that guard against the external environment whenever the skin is damaged.
When the barrier is broken, sequences of a physiological and biochemical process of wound healing stages begin to treat the wound. The healing procedures are divided into clotting of the blood, inflammation, growth of tissue, and tissue remodeling stages. Blood clotting may be considered to be part of the inflammation stage instead of a separate stage.
Types of wound and healing process
There are three types of healing - healing by the primary or secondary closure and delayed primary or tertiary closure. Most wounds heal by primary intention. It is a situation where wound edges are estimated and are secured with closure materials like staples, sutures, and steri-strips among others. These wounds are clean, sterilized or non-infected with negligible tissue deficiencies. The types of wounds that needs these healing process includes, surgical wounds, lacerations, and clean cuts. They exhibit minimal scarring because no tissue defect exists and new dermal tissue is only needed to fill the opening across the closely aligned wound edges.
Wounds restorations by secondary intention are usually prolonged wounds. These wounds have big tissue wounds that are not possible to close with ease because of the extent of the damage. Healing takes place gradually through the development of new tissue to fill the cavity hence closing the wound. These usually cause scars since the new skin must develop across a larger area. The types of wounds healing by secondary intention includes diabetic wounds, leg ulcers, and pressure injuries.
Some lacerations may need prolonged closure because of contamination, the need for the development of new granulation tissue to shield exposed fascia, bone or tendon before definitive or primary closure. This kind of healing is known as a delayed primary closure or tertiary closure. Skin grafting is often applied where delayed primary closure may be required. The types of these wounds include abdominal wound that is initially left open to allow for drainage but is later closed.
Factors impairing wound healing
Several factors can affect the healing process which includes, illness, age, treatments, psychological or social factors, or when any of these factors combine. Any condition that lessens perfusion to the wound will bar the healing process. The pre-operative time, surgical procedure and post-operative pain can also cause stress and anxiety which trigger physiological responses that restrict the process of healing. Psycho social influences such as no social or family support, being dependent, depression and poverty initiate similar anxiety that may cause complications of wound healing process or delay healing.
Locally wound characteristics also influence reparative processes. Tissue type, infection, and inflammation, moisture balance, wound edges, wound temperature and the size of the microcirculation to supply oxygen to the wound bed and surrounding tissues all influence healing.
Stages of wound healing
The natural process of wound healing takes place through four phases. All the four phases are important and must occur in the process for a wound to heal. Although the organized stages of wound healing process are linear, wound healing can delay due to internal and external conditions the patient may incur. The stages of the wound healing process are explained below:
1. Rapid hemostasis phase
This is the phase where the wound gets closed by clotting of the blood which is known as hemostasis. The process begins when blood comes out of the body and happens when blood vessels tighten to control the flow of blood. The platelets then stick together to cover the opening in the sides of the blood vessel.
After that, coagulation takes place and strengthens the seal formed by the platelets with a web of fibrin similar to a binding agent. The phase happens very fast since the platelets stick to the endothelium surface in a matter of seconds after the rapture of the blood vessel's wall.
Then the first strands of fibrin start sticking in approximately a minute. As the mesh of fibrin starts to form, the blood transforms from fluid to gel via coagulants and the discharge of prothrombin. The creation of a clot traps the platelets and the blood cells in the areas that are wounded. The thrombus is critical in the natural process of wound healing but becomes problematic when it separates from the vessel wall and travels through the circulatory system and could trigger a stroke or even a heart attack.
2. The Inflammatory phase
Inflammation is the stage that follows the hemostasis, the first stage of the wound healing process. The phase starts immediately when the bruised blood vessels leak a mixture of salt, water and protein known as transudate and causes localized swelling. It is the stage where bleeding and prevention of infection is controlled.
The fluid inflammation lets healing cells to go to where the wound is. During this process, injured cells, pathogens, and bacteria are eliminated from the injury. The white blood cells, growth aspects, enzymes, and nutrients cause the puffiness, heat, redness, and pain which are common at this time of curing. Inflammation is a natural part of the wound healing process and becomes an issue if extended or extreme.
When inflammation occurs, the body discharges different types of cells, including those that are accountable for migration and proliferation. Proliferation is the same as hemostasis since cells work to further tighten the blood vessels.
3. The Phase of proliferation
The proliferative phaseis the third stage of the wound healing process. This process occurs when when the wound is formed again with new tissue consisting of collagen and extracellular matrix. During this phase, the injury diminishes as fresh tissues are created. A new system of blood vessels must also be formed for the granulation tissue to be well and get adequate nutrients and oxygen.
Contraction is caused by myofibroblasts which grip the edges of the wound and pull them together by a method same as of smooth muscle cells. In healthy stages of the natural process of wound healing, the texture of the granulation tissue is pink or red and uneven. Furthermore, healthy granulation tissue does not hemorrhage with ease. Dark granulation of the tissue could indicate infection or ischemia.
In the last stage of the proliferation, epithelial cells reappear in the wound. It is critical to note that epithelialization takes place quicker when wounds are kept moist. Whenever occlusive or semiocclusive bandages are applied less than 48 hours after injury, they will preserve the correct humidity of the tissue to enhance epithelialization.
4. The maturation or re-modelling phase
It is the stage where collagen is modified from type III to type I and the wound closes completely. Old cell that were used to heal the wound are eliminated through apoptosis because they are not needed anymore. When collagen lays down during the previous phase, it is jumbled and the wound is seems swollen. During the maturation phase, collagen is aligned along tension lines and water is absorbed again so the collagen fibers can be close and cross-link. Cross-linking of collagen lessens the thickness of the scar and also strengthens the part of the skin around the injury.
The maturation stage starts approximately three weeks after an injury and can last for a year or even longer. Even with cross-linking, healed wound areas are still weaker than unscathed skin, possessing just 80% of the tensile strength of healthy skin.
Factors influencing healing of a wound
- The site of the wound
- Wounded Structures
- Mechanism of wounding
- Significant loss of tissue
- Use of cytotoxic drugs
- Diabetes mellitus
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Understanding the kind of healing intention and to recognizing the stage of reparation and its progression to gauge whether wounds are healing as they should, is important. Knowing the signs and symptoms of inflammation and infection like new or aggravated pain, extended inflammation, new or spreading erythema, an increase in exudate or change in exudate color with or without smell, variation in color of the wound or increased temperature should ensure prompt review of the wound. Infected wounds held in the inflammatory stage cannot continue with the natural process of wound healing. Thorough wound assessment and investigations are required to determine the reason why wounds won’t heal. Accurate documentation of the stage of the process of wound healing lets caregivers develop suitable wound management strategies to protect the wound and expedite healing the healing process.
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