All skin wounds are defined as disruptions of the skin that cause a repair process to start in the body.  There are two types of wounds – acute and chronic.  Acute wounds usually heal within an expected time frame.  Chronic wounds can remain for weeks, months and even years. Patients often have multiple medical conditions that impede or delay the healing process.

Conditions that affect wound healing include:

• Diabetes
• Kidney dialysis
• Age
• Swelling
• Cancer
• Medications
• Infection
• Poor circulation
• Poor nutrition

A chronic wound is a wound that does not heal in an orderly way and in a predictable amount of time, as most wounds do.  Wounds that do not heal within three months are often considered chronic.  Chronic wounds seem to be stuck in one or more of the phases of wound healing.  For example, chronic wounds often remain in the inflammatory stage for too long.  In acute wounds, there is a precise balance between production and degradation of molecules such as collagen; in chronic wounds this balance is lost and degradation plays too large a role.
Chronic wounds may never heal or may take years to do so. These wounds cause patients emotional and physical stress and create a financial burden on patients and the healthcare system.
Acute and chronic wounds are at opposite ends of a spectrum of wound healing types that progress toward being healed at different rates.

Epidemiology

Chronic wounds mostly affect people over the age of 60.  The incidence is 0.78% of the population and the prevalence ranges from 0.18 to 0.32%.  As the population ages, the number of chronic wounds is expected to rise.

Types

The vast majority of chronic wounds can be classified into three categories: venous ulcers, diabetic, and pressure ulcers.  A small number of wounds that do not fall into these categories may be due to causes such as radiation poisoning or ischemia.

Venous ulcers

Venous ulcers, which usually occur in the legs, account for about 70% to 90% of chronic wounds. and mostly affect the elderly.  They are thought to be due to venous hypertension.  This is caused by improper function of valves which exist in the veins to prevent blood from flowing backward.  Ischemia results from the dysfunction and, combined with reperfusion injury, causes the tissue damage that leads to the wounds.

Diabetic ulcers

Another major cause of chronic wounds, diabetes, is increasing in prevalence.  Diabetics have a 15% higher risk than the general population for amputation due to chronic ulcers.  Diabetes causes neuropathy, which inhibits nociception and the perception of pain.  Diabetic patients may not initially notice small wounds to legs and feet, and then fail to prevent infection or repeated injury.  Further, diabetes causes immune compromise and damage to small blood vessels, preventing adequate oxygenation of tissue, which can cause chronic wounds.

Pressure ulcers

Another leading type of chronic wounds is pressure ulcers, which usually occur in people with conditions such as paralysis that inhibit movement of body parts that are commonly subjected to pressure such as the heels, shoulder blades, and sacrum.  Pressure ulcers are caused by ischemia that occurs when pressure on the tissue is greater than the pressure in capillaries.  This results in restricted blood flow into the area.  Muscle tissue, which needs more oxygen and nutrients than skin, shows the worst effects from prolonged pressure.  As in other chronic ulcers, reperfusion injury damages tissue.

Pain and chronic wounds

Chronic wound patients often report pain as dominant in their lives.  It is recommended that healthcare providers handle the pain related to chronic wounds as one of the main priorities in chronic wound management (together with addressing the cause).  Six out of ten venous leg ulcer patients experience pain with their ulcer, and similar trends are observed for other chronic wounds.
Persistent pain (at night, at rest, and with activity) is the main problem for patients with chronic ulcers. Patients are often frustrated with ineffective pain relief and difficulty in caring for the wound.

Contributing factors

In addition to poor circulation, neuropathy, and impaired mobility, factors that contribute to chronic wounds include systemic illnesses, age, and repeated trauma.  Other conditions that may contribute to the formation of chronic wounds include vasculitis (an inflammation of blood vessels), immune suppression, pyoderma gangrenosum, and diseases that cause ischemia.  Immune suppression can be caused by illnesses or medical drugs (ie. steroids) used over a long period.  Emotional stress can also negatively affect the healing of a wound, possibly by raising blood pressure and levels of cortisol, which lowers immunity.

Another factor that may contribute to chronic wounds is old age.  The skin of older people is more easily damaged.  Older cells do not proliferate as fast and may not have an adequate response to stress in terms of gene upregulation of stress-related proteins.

Conditions that can lead to ischemia are especially likely to contribute to chronic wounds.  These include chronic fibrosis, atherosclerosis, edema, sickle cell disease, and arterial insufficiency-related illnesses.
Repeated physical trauma plays a role in chronic wound formation by continually initiating the inflammatory cascade. The trauma may occur by accident, for example when a leg is repeatedly bumped against a wheelchair rest.

Pathophysiology

Chronic wounds may affect only the epidermis and dermis, or they may affect tissues all the way to the fascia.  They may be formed originally by the same things that cause acute ones, such as surgery or accidental trauma, or they may form as the result of systemic infection, vascular, immune, or nerve insufficiency, or as a complication of another disease such as cancer or a metabolic disorder.  A wound becomes chronic when the body’s ability to deal with the damage is overwhelmed by factors such as repeated trauma, continued pressure, ischemia, or illness.  Current researchers now understand some of the major factors that lead to chronic wounds, among which are ischemia, reperfusion injury, and bacterial colonization.

Ischemia

Ischemia is an important factor in the formation and persistence of wounds, especially when it occurs repetitively (as it usually does) or when combined with a patient’s old age.  Ischemia causes tissue to become inflamed and cells to release factors that attract neutrophils such as interleukins, chemokines, leukotrienes, and complement factors.
While they fight pathogens, neutrophils also release inflammatory cytokines and enzymes that damage cells. One of their important jobs is to produce ROS to kill bacteria, for which they use an enzyme called myeloperoxidase.  The enzymes and ROS produced by neutrophils and other leukocytes damage cells and prevent cell proliferation and wound closure by damaging DNA, lipids, proteins the ECM, and cytokines that speed healing.  Neutrophils remain in chronic wounds for longer than they do in acute wounds, and contribute to the fact that chronic wounds have higher levels of inflammatory cytokines and ROS.  Since wound fluid from chronic wounds has an excess of proteases and ROS, the fluid itself can inhibit healing by inhibiting cell growth and breaking down growth factors and proteins in the ECM.

Bacterial colonization

Since more oxygen in the wound environment allows white blood cells to produce ROS to kill bacteria, patients with inadequate tissue oxygenation (for example, those who suffered hypothermia during surgery) are at higher risk for infection. The host’s immune response to the presence of bacteria prolongs inflammation, delays healing, and damages tissue.  Infection can lead not only to chronic wounds but also to gangrene, loss of the infected limb, and death of the patient.
Like ischemia, bacterial colonization and infection damage tissue by causing a greater number of neutrophils to enter the wound site.  In patients with chronic wounds, bacteria with resistances to antibiotics may have time to develop.  In addition, patients that carry drug resistant bacterial strains such as methicillin-resistant Staphylococcus aureus (MRSA) have more chronic wounds.

Growth factors and proteolytic enzymes

Chronic wounds also differ in makeup from acute wounds in that their levels of proteolytic enzymes such as elastase and matrix metalloproteinases (MMPs) are higher, while their concentrations of growth factors such as Platelet-derived growth factor and Keratinocyte Growth Factor are lower.
Since growth factors (GFs) are imperative in timely wound healing, inadequate GF levels may be an important factor in chronic wound formation.  In chronic wounds, the formation and release of growth factors may be prevented, the factors may be sequestered and unable to perform their metabolic roles, or degraded in excess by cellular or bacterial proteases.
Chronic wounds such as diabetic and venous ulcers are also caused by a failure of fibroblasts to produce adequate ECM proteins and by keratinocytes to epithelialize the wound.  Fibroblast gene expression is different in chronic wounds than in acute wounds.
Though all wounds require a certain level of elastase and proteases for proper healing, too high a concentration is damaging.  Leukocytes in the wound area release elastase, which increases inflammation, destroys tissue, proteoglycans, and collagen, and damages growth factors, fibronectin, and factors that inhibit proteases.  The activity of elastase is increased by human serum albumin, which is the most abundant protein found in chronic wounds.  However, chronic wounds with inadequate albumin are especially unlikely to heal, so regulating the wound’s levels of that protein may in the future prove helpful in healing chronic wounds.
Excess matrix metalloproteinases, which are released by leukocytes, may also cause wounds to become chronic.  MMPs break down ECM molecules, growth factors, and protease inhibitors, and thus increase degradation while reducing construction, throwing the delicate compromise between production and degradation out of balance.

Treatment

Though treatment of the different chronic wound types varies slightly, appropriate treatment seeks to address the problems at the root of chronic wounds, including ischemia, bacterial load, and imbalance of proteases.  Various methods exist to deal with these problems, including antibiotic and antibacterial use, debridement, irrigation, low intensity laser therapy, hyperbaric therapy, vacuum-assisted closure, warming, oxygenation, moist wound healing, removing mechanical stress, and adding cells or other materials to secrete or enhance levels of healing factors.

How Low Intensity Laser Therapy is applied to Wounds

LLLT is applied to an open wound by use of large treatment head arrays and the probe. The probe can either be placed in contact with the wound or held just above it.  In addition to treating the wound bed it is helpful to treat the skin around the wound with a single probe at points about 1–3m from the wound margin and about 2–4m apart.  Laser dosages and treatment session lengths vary depending on the type of wound, location and the individual’s health history.
When treating acute inflammation in a chronic wound where debridement is necessary, it should precede treatment with LILT.

The healing of acute and chronic wounds can only be stimulated by LILT if they are healing suboptimally.  In these wounds, granulation tissue production and wound contraction is achieved with LILT.
Inflammation is resolved more rapidly and the proliferative phase of healing begins much sooner

Preventing and treating infection

To lower the bacterial count in wounds, therapists may use topical antibiotics, which kill bacteria and keep the wound environment moist.  This is important for speeding the healing of chronic wounds.  Some researchers have experimented with tea tree oil, an antibacterial agent which also has anti-inflammatory effects.  Disinfectants are contraindicated because they damage tissues and delay wound contraction. Further, they are rendered ineffective by organic matter in wounds like blood and exudate and are thus not useful in open wounds.
A greater amount of exudate and necrotic tissue in a wound increases likelihood of infection by serving as a medium for bacterial growth away from the host’s defenses.  Since bacteria thrive on dead tissue, wounds are often surgically debrided to remove the devitalized tissue.  Debridement and drainage of wound fluid are an especially important part of the treatment for diabetic ulcers, which may create the need for amputation if infection gets out of control.  Mechanical removal of bacteria and devitalized tissue is also the idea behind wound irrigation, which is accomplished using pulsed lavage.

Treating painful wounds

Persistent chronic pain associated with non-healing wounds is caused by tissue (nociceptive) or nerve (neuropathic) damage and is influenced by dressing changes and chronic inflammation.  Chronic wounds take long time to heal and patients can suffer from chronic wounds for many years.  Chronic wound healing may be compromised by coexisting underlying conditions, such as venous valve backflow, peripheral vascular disease, uncontrolled edema and diabetes mellitus.  Laser therapy is used to reduce and eliminate pain with chronic wounds.
If wound pain is not assessed and documented it may be ignored and/or not addressed properly.  It is important to remember that increased wound pain may be an indicator of wound complications that need treatment, and therefore practitioners must constantly reassess the wound as well as the associated pain.
Optimal management of wounds requires holistic assessment.  Documentation of the patient’s pain experience is critical and may range from the use of a patient diary, (which should be patient driven), to recording pain entirely by the healthcare professional or caregiver.  Effective communication between the patient and the healthcare team is fundamental to this holistic approach.  The more frequently healthcare professionals’ measure pain, the greater the likelihood of introducing or changing pain management practices.

Treating ischemia and hypoxia

Blood vessels constrict in tissue that becomes cold and dilate in warm tissue, altering blood flow to the area. Thus keeping the tissues warm is probably necessary to fight both infection and ischemia.  Some healthcare professionals use ‘radiant bandages’ to keep the area warm, and care must be taken during surgery to prevent hypothermia, which increases rates of post-surgical infection.
Underlying ischemia may also be treated surgically by arterial revascularization, for example in diabetic ulcers, and patients with venous ulcers may undergo surgery to correct vein dysfunction.
Diabetics (and others) may also have their tissue oxygenation and other celluar properties increased by Laser Therapy, which can compensate for limitations of blood supply and correct hypoxia.  In addition to killing bacteria, higher oxygen content in tissues speeds growth factor production, fibroblast growth, and angiogenesis.  However, increased oxygen levels also means increased production of ROS.  Antioxidants (molecules that can lose an electron to free radicals without themselves becoming radicals) can lower levels of oxidants in the body and have been used with some success in wound healing.