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Dermis
Residing just below the epidermis is the dermis, which constitutes 90% of total skin thickness. Because of its rich collagen content, the dermis is the strength layer of the skin. In addition, it contains blood vessels, nerve endings, hair follicles, and immune cells that act as sentries against infection and cancer.
These two layers are draped over a deeper subcutaneous layer comprised of fatty tissue, blood vessels, and nerves which is generally protected from injury by the overlying epidermal and dermal covering.
Wound Healing
Under normal conditions, the process of healing occurs in three overlapping phases. Roughly speaking, these are divided into inflammatory, proliferative, and remodeling phases and involve contraction (downsizing of the wound), epithelialization (creation of new epithelial cells), and deposition of connective tissue.
Inflammation
When skin is injured-whether in a planned injury such as a surgical incision or as the result of trauma-an inflammatory phase begins. This is initiated by the release of several chemicals from both platelets (tiny cells which initiate the clotting mechanism) and the surrounding injured tissue. The site of injury turns red, becomes swollen, and displays all the normal properties we commonly associate with an acute wound.
This initial inflammatory reaction is critical because it sets the stage for a cascading process that eventually should lead to normal wound healing. Chemicals released during this phase signal messengers to draw critical inflammatory cells into the site of injury. These cells break down and remove injured, devitalized tissue and clean the wound in preparation for the laying down of new tissue. During this phase, cells of the immune system are also attracted by these chemical messengers and modulate the overall generalized inflammatory reaction, though their specific functions are really not known.
Proliferation
The initial inflammatory phase sets the stage for what comes next -the proliferative stage. During this phase, tissue integrity is restored as the release of various growth factors and chemical messengers stimulate the creation, migration, and proliferation of new healthy cells. Specialized cells called fibroblasts lay down a collagen matrix to restore tensile strength of the wound. In addition, in-growth of new blood vessels ensures that adequate nutrients and oxygen are delivered to the site of the healing wound.
Remodeling
The final segment, the remodeling phase, can last for several weeks to several months and involves fine tuning of the wound bed. During this time, collagen is produced and degraded at about the same rate so that overall collagen content remains essentially unchanged. What does change is the organization of the collagen. By structurally remodeling and rearranging orientation of the collagen, the wound is able to approximate-though never fully reach-the strength it had prior to injury.
Scars
A scar is the end result of your body’s attempt to close a wound, and it is a normal process that occurs whenever an injury involves the dermis. Superficial cuts and scrapes that injure the epidermis and superficial dermal layer alone generally heal without scarring. If the wound is closed under optimal conditions (for example a surgical incision) and the edges are brought together under minimal tension, there is a good chance you will achieve that fine thin scar that in time will be barely visible. The body wants to take a wound and make it smaller, and has specialized cells called myofibroblasts that draw the wound edges together during the healing process and convert a large wound to a smaller wound.
If instead, the wound is dirty, very large, or requires a lot of force to bring it together, your long-term result may not be optimal and you may see a thick scar.
Scars take time
It’s important to remember that a scar takes up to a year-and sometimes longer-to attain its final appearance. Many people get frustrated as their early scars take on a reddened, heaped-up appearance in the first few months after injury, and look worse as the days progress. If this same scar is evaluated at twelve months, it usually looks much different and has healed close to its final appearance.
But what happens when this final appearance is not optimal?
Hypertrophic scars
Some scars-the result of variables such as infection, excessive tension, or generally poor wound healing- develop into thick raised lines that are simply not attractive. When a scar is heaped-up and prominent but does not extend beyond the zone of original injury, it is referred to as a hypertrophic scar.
Hypertrophic scars can be treated in several ways. If you have always healed poorly, chances are you will continue to heal poorly. Some people simply do not form attractive scars. But if previous injuries led to more satisfactory healing, you may want to consider a scar revision in which the scar is cut out and the incision re-closed. Sometimes this will provide an acceptable long-term result but there is no guarantee. Before your embark on revision, make sure to discuss the procedure with your physician and gain his or her impression of the likelihood of success before jumping in.
Keloid scars
Another group of scars is the keloids. Keloids are generally the result of a poorly-understood genetic tendency to develop large scar growths at the site of even the smallest injury. The most common keloid scars develop after ear piercing. Although certain areas of the body are more susceptible to this (e.g: earlobes, chest wall, shoulders), if you previously healed with a keloid, chances are you will heal again with a keloid. These are very difficult to treat and commonly recur.
Factors That Affect the Wound Healing Process
Because of the complexity of the wound healing process, several factors can discourage adequate wound healing. Some of these factors we can control-others we cannot-and include the following:
Age
Wounds heal slower and less effectively as we age. Numerous studies have documented that our cellular healing mechanisms are slower to respond and operate less effectively as we get older leading to less optimal wound healing.
Infection
An infected wound takes much longer to heal because the body’s local resources are divided between the healing process and the need to fight the infection. Because of this, the wound stays in the inflammatory phase for a much longer period of time and the overall results are generally poorer than if the wound bed were clean.
Poor nutrition
The complex process of wound healing requires a number of vitamins and other chemical cofactors to complete its job. Without these building blocks, wound healing takes longer and is generally compromised. An example of this involves the early sailors who developed scurvy (vitamin C deficiency) because of their lack of access to fresh fruit. They commonly developed bleeding gums and had tremendous difficulty healing even the most minor wounds.
Unfortunately, poor wound healing from a lack of vitamin C does not suggest that overcompensating or megadosing with vitamin C will speed up the normal healing process. To provide the appropriate building blocks for repair, just make sure to follow general nutritional guidelines and eat a healthy diet.
Immunosuppression
Patients whose immune systems are compromised (whether the result of disease or the result of chemotherapy) generally display poor wound healing. The normal wound healing process requires the recruitment of the immune system to properly clear the wound of debris and prepare the local environment for repair. When this arm of the healing process is compromised, the result is not only delayed healing, but often ineffective healing as well.
For example, chemotherapy medications attack rapidly dividing cells in an attempt to fight cancer. The problem here is that the drugs do not distinguish between the rapidly dividing cancer cells and those that are dividing to heal a wound. Because of this, wounds generally take much longer to heal in patients on chemotherapy and will continue to do so until the drugs are stopped.
Other medications
Many drugs can affect normal wound healing at various levels. There is a long list of medications that may either prevent or at least slow down normal wound healing. Because of this, it is critical to discuss all current medications with your physician to determine if any changes can be made.
Radiation
Radiation impairs the cells responsible for collagen production, and may actually shrink the numbers of these cells, which disrupts the wound healing process, and also creates a wound generally weaker in strength. Radiation also can harm the delicate blood vessels that course through the area exposed to it. The tissue is left with a poor oxygen supply and as a result; the healing process is again compromised. The effects of radiation on wound healing are felt right after exposure, and for many years thereafter.
Diabetes
When wounds develop in people with diabetes, their chronically elevated levels of blood sugar incapacitate the wound healing response. And not only can diabetes interfere with the healing process, it can also cause the development of new wounds. Long-term diabetics commonly develop nerve damage in their legs. This damage to the nerves reduces their protective capacity and increases the likelihood of new wound development. It also increases the risk that the body will not recognize new wounds when they develop.
Peripheral vascular disease
Peripheral vascular disease is a problem with narrowing of the limb arteries, which results in poor oxygen delivery to the areas beyond the narrowing. All tissue requires a baseline level of oxygen for survival. When this level is reduced, the local tissue dies and with it the capacity to regenerate. Patients with peripheral vascular disease should be treated in conjunction with a vascular specialist to assure that the appropriate steps for restoration of adequate blood supply and tissue oxygenation are undertaken in tandem with attempts at wound healing.
Systemic illness
Any major illness that affects the whole body also affects the body’s ability to repair itself. During a systemic illness, the body requires tremendous energy and resources to repair itself, and wound healing is temporarily compromised. Healing will not stop entirely, but the process will not operate as efficiently or effectively as it would in a healthier state.
Smoking
Cigarette smoke contains a number of harmful substances including nicotine, carbon monoxide, and hydrogen cyanide.
Aside from its extreme addictive potential, nicotine has been shown to cause constriction of blood vessels in the subcutaneous tissue for up to 50 minutes after smoking a single cigarette. This constriction decreases the blood flow to the area and therefore decreases the ability to deliver oxygen to the wound. In addition, smoking also inhibits the production of several cell types critical to the healing process and promotes the clumping of platelets, which increases the risk of blood clots.
Carbon monoxide is a poison that competes with oxygen in the bloodstream. It decreases the process of oxygenation in the tissue, which can actually lead to tissue death.
Hydrogen cyanide is a poison that selectively blocks intracellular metabolism and the ability of cells to use oxygen.
Stress
Although temporary periods of stress can be motivating, chronic stress can become a destructive force that effectively disturbs the healing process. During prolonged periods of stress, your body’s level of hormones (more specifically the steroid hormones) become markedly elevated. Your body reacts to stressful conditions by marshalling its energy and resources to manage the stressful condition at hand. When the stress is temporary, this is referred to as the "fight or flight" phenomenon. When the stress is more long-lasting or becomes chronic, instead of creating conditions conducive to healing, the elevation of various stress hormones and internal messengers creates and environment that favors tissue breakdown.
Chronic Wounds
When healing stops, for whatever reason, an acute wound can develop into a chronic wound that simply will not heal. When this happens, the local wound environment can become unfavorable to healing. For example, chronic wounds tend to have a much different composition of growth factors present in the wound bed, which actually favor non-healing. If these destructive factors are allowed to persist, the wound will either never heal or will only heal over a very long period of time. The wound must be cleaned of these harmful factors before normal healing will occur.
Treating a chronic wound
A wound must be clean and free of infection in order to heal. If the wound is clean, the treatment is easy. Gentle, daily dressing changes allow the body’s own mechanisms to continue the healing process. If the wound is infected, however, the body has to divert a majority of its resources away from healing and focus on fighting an active infection. Devitalized or grossly infected tissue must be removed in order for the healing process to continue. After the removal of devitalized tissue, special dressing changes can be made to eliminate any residual infection.
Another way to encourage wound healing is to use vacuum-assisted closure. This involves placing a sealed sponge system over the wound, which is then placed on a low vacuum setting for a period of weeks or months as the wound heals. Several studies have shown this device to be very effective in speeding up the wound healing process in acute and chronic wounds. And, most importantly, the device is painless and the cost is generally covered by insurance.
The wound that still won’t heal
If the measures above are taken and do not speed the wound healing process, then other underlying causes must be identified and addressed.
For example, if the patient has peripheral vascular disease and has severely compromised blood flow, the wound will not effectively heal until blood flow is improved. This patient may need a surgical procedure to improve blood supply before there is any chance of healing the wound.
This same scenario applies to the many other reasons for poor wound healing. If we don’t address the reason the wound hasn’t healed in the first place, we’ll probably never be able to heal it.
Pressure Sores
The next time you sit for a long time, notice how often you feel the need to shift your weight or reposition yourself. This is generally an unconscious act, but it’s actually critical in reducing pressure on various key pressure points throughout the body.
Sustained pressure on any area of our body can impede local blood supply and cause tissue ischemia or tissue death, and there are some people who cannot avoid sustained pressure. One example are paraplegic patients who not only cannot move their lower extremities but who also cannot feel pain or pressure as a result of their injury. These people must be closely watched for local tissue compromise and impeding skin breakdown. Elderly bedridden patients are also prone to pressure sores, as they often remain in the same position for prolonged periods of time. They can develop pressure sores (decubitus ulcers) at pressure points on the lower back, hips, heels, and the lower extremities.
Who is at risk? The following are risk factors for the development of pressure sores:
- Altered mental status or sensory perception
- Inability to control bladder or bowel functions
- Exposure to moisture
- Immobility or inability to shift weight in an effective manner
- Exposure to friction or shear forces
- Poor nutritional status
The best treatment for pressure sores is prevention. Unfortunately, pressure sores are a common problem, and very often they are the result of oversight or simple negligence. Once recognized, however, appropriate treatment can begin.
Conclusion
Preventing wounds can be as simple as alleviating daily pressure or as complex as addressing a chronic or acute underlying medical condition. Whatever the cause, prompt intervention can often be the difference between a wound that heals and a wound that does not.
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