The skin is the largest organ in the body. It is the first line of defense against environmental attacks on the body. Once compromised, the second line of defense, our immune system, kicks in to restore balance and start the process of healing. No matter the cause of the wound, the stages of healing are the same. Many factors can affect wound healing and play a part in how long it takes for the wound to heal.
Superficial wounds, that is a wound that affects the epidermis (the outer layer of skin) heal quickly. An example is a paper cut or scrapes on the knee. Deeper wounds that go into the dermis, the second layer just below the epidermis take a little longer to heal. This type of wound can be caused by a cut with a knife.
Wounds can be caused by injury, pressure, or poor blood flow to a specific area. These wounds often become chronic and take a longer time to heal. A chronic wound is considered to be a non-healing wound after 3 months. Patients with vascular disease, arterial or venous can develop non-healing wounds from minor skin injuries.
Burns are another type of wound that requires complicated treatment plans. They often require surgical intervention and debridement (removal of dead skin). This can be done surgically or by applying enzymatic dressings that breakdown the dead cells.
Last, surgically created wounds can be closed at the time of surgery or left open to heal slowly. With a closed surgical wound, the skin is pulled together and closed by either suture, staples, or with a liquid bandage (glue). This type of wound heals by primary intention, from the top (skin level) down. A wound that is left open heals from the bottom up (secondary intention). This is done if the wound is infected. It allows for infection to drain from the wound. The body will build new tissue and finally skin to close the wound.
A series of 4 phases in wound healing is the same for all wounds and the result is the reconstruction of tissue and closure of the skin. The phases overlap.
The first phase is hemostasis and this stage begins as soon as the injury occurs. The body controls bleeding by constriction of the vessels and sending platelets (blood components responsible for clotting) to form a clot. The platelets bind to the exposed collagen in the tissue which then releases growth factors and inflammatory cells. This allows the clot to form, stopping additional blood loss.
The second stage of wound healing is the inflammatory stage. Once the wound as stabilized, the inflammatory cells travel to the wound after the platelets. Vasodilation of blood capillaries begins after a few days of the injury. This allows blood flow to the wound to begin the healing process. White blood cells enter the wound and attack bacteria and dead tissue within. As the wound is cleared of unwanted debris, growth factors are released from macrophages (part of white blood cells) into the wound. This is essential for healing. If macrophages are inhibited, delayed healing occurs.
The third phase of wound healing is the proliferation and occurs 3-21 days after injury. The goal of this phase is to fill the wound defect by a process call angiogenesis. Angiogenesis is triggered by the growth factors released in the first two phases of healing and is responsible for supplying oxygen, glucose (sugar for cellular energy), and other factors needed for healing. Granulation tissue and vascular support are created and are essential for the final phase of healing.
Maturation is the final stage of wound healing. Collagen building and remodeling of granulation tissue create scar tissue. The scar tissue continues to strengthen over the next 4-6 weeks and will have 80% of the strength of normal tissue after 3 months. Initially, the scar will be firm and red in color. Nine to 12 months after wound healing, the scar will soften and become lighter in color. It is recommended to avoid sun exposure to the scar as this may tattoo the scar and change the color permanently.
Age plays a role in healing. As we age, all processes in the body slow down, including wound healing. The elderly population has fragile skin. Decreased blood flow causes the skin to be dry. Wounds need a moist environment for proper healing. It also decreases the thickness of the dermis causing thin, transparent skin. The aging patient may not show signs and symptoms of infection such as fever, redness, or swelling at the site of the wound.
Nutrition is very important in wound healing. The body utilizes lots of energy to build and repair, requiring increased caloric intake. Protein is needed to build collagen and strong tissue. If protein intake is inadequate, the body will pull the protein needed for healing from muscle tissue. Remember, the heart is a muscle. Carbohydrates and fats are the sources of energy in the body and more is required for wound healing. Other vitamins needed for healing are vitamin C, A, and E to name a few
Obesity affects wound healing. The rate of infection is higher in patients that are overweight. Blood supply to adipose (fat) tissue is less than the blood flow to muscle or other organs. Obese patients often have other health conditions such as diabetes or high blood pressure that can slow wound healing.
Poor blood circulation is another factor that delays wound healing. Blood carries vital nutrients and oxygen to the wound to assist with the healing process. Poor blood circulation can be caused by vascular disease, heart disease, a compromised respiratory system, poor kidney function, and smoking. Nicotine is a vasoconstrictor. That means it causes the vessels to shrink, making blood flow slower to the tissues that need oxygen and nutrients. The carbon monoxide inhaled from smoking binds to the hemoglobin in the red blood cells, not allowing oxygen to bind to the hemoglobin and be carried to the wound.
People with compromised immune systems are at higher risk for delayed wound healing. They have a higher risk of infection in the wound bed. An infection will delay healing as well. Those taking steroids or receiving radiation or chemotherapy are immune-compromised. Diabetes and HIV will affect the immune system along with those taking biological medication for autoimmune conditions like Crohn’s disease, psoriatic arthritis, rheumatoid arthritis, lupus, and ulcerative colitis to name a few.
Decrease mobility can lead to skin breakdown and delayed wound healing. For example, a patient may have difficulty moving in bed after having a stroke. Constant pressure from remaining in the same position for long periods of time decreases blood flow and oxygenation to points of pressure, causing the skin to breakdown. This is known as a pressure injury (ulcer).
Wound healing is dependent on many factors as mentioned previously. The length of time it takes to heal a wound varies greatly and is determined by the type of wound, how deep or big the wound is, and other health factors of the person with the wound. Age, weight, nutritional status, vascular and respiratory status, immune system deficiencies, and mobility play major roles in how quickly the wound will heal. The elderly and those with diabetes are at high risk of poor wound healing and should be diligent with the safety and monitoring of skin. If you have a concern about an open wound, contact your primary care physician for evaluation. The faster the wound is treated, the less likely you are to develop skin infections and maintain your body’s first line of defense.
Author Profile: Christine Kijek, Registered Colorectal Nurse
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