Why Is a Moist Environment Essential for Wound Healing?
”Moist Wound Healing Theory“
Moist wound healing is the practice of keeping a wound in an optimally moist environment to promote faster healing. Research has shown that moist wound healing is three to five times quicker than the healing of wounds that are allowed to dry out.
1. The birth of the theory of wound healing in a moist environment
British researcher George D. Winter described the benefits of?moist wound healing?in the 1960s. His research demonstrated that moist environments optimize healing of wounds. In the 1970s and 80s, moist wound healing became a standard practice. During the late 1980s and 90s, the field of moist wound dressings was thoroughly researched and many new?wound dressing products?were developed such as hydrogels, foams and alginates. Increasingly, wound dressings began to be seen as not just protective measures, but active parts of the healing process.
2. What are the benefits of Moist Wound Healing?
Before the theory of moist wound healing was developed, dressings were used primarily to absorb fluid, protect the wound from injury and limit exposure to infections. The natural scab on the wound was considered to be a normal part of the healing process. However, moist healing theory discovered that by preventing the body from developing a scab, wounds could not only be healed faster, but also better. Here are some of the benefits of moist wound healing:
Wound Healing Takes Less Time: When the body creates a scab or eschar, that requires time and energy. Additional energy is required to break down the scab after the wound is healed. In a moist wound healing environment, the body is able to focus on healing the wound rather than protecting it, and wounds heal faster.
Keratinocyte Cells Function More Easily: Keratinocytes, a major component of the epidermis, have several critical roles in wound healing. The cross-talk between keratinocytes and the other types of cells involved in wound healing is crucial for effective closure of the wound. In dry wounds, keratinocytes must burrow underneath the wound bed in order to find a moist area to move forward. In a moist wound healing environment, keratinocytes can easily travel across the wound surface more quickly and easily.
Autolytic Debridement is Facilitated: Moist environments trap endogenous proteolytic enzymes in the wound. This allows those enzymes to more efficiently perform autolytic debridement to break down necrotic tissue. Along with speeding healing, moist wound environments allow for the body’s natural process of healing to work more effectively.
Decreases Incidence of Wound Infection: A moist wound environment reduces the possibility of infection by creating a hypoxic environment in the wound bed which promotes angiogenesis, decreases the pH, and makes the wound area inhospitable to bacteria.
Preserves Growth Factors in Wound Fluid: Growth factors are natural proteins which control key cellular activities during the tissue repair process. Moist wound healing allows the growth factors to be preserved on the wound bed to repair tissues more quickly.
Stimulates Collagen Synthesis: Moist wound healing promotes production of collagen by the fibroblasts. Since collagen is the basis of the new tissue that will heal the wound, this increased production helps the body lay down the matrix for new tissue more quickly so that the cells necessary for healing are attracted.
Reduces Pain: Another benefit of moist wound treatment is that there is reduced pain. With less pain, there is also a reduced stress response and less fatigue in patients which also aids in the healing process. Decreased pain can also lead to better patient mobility, which improves circulation, oxygenation, and allows for better healing.
Reduces Scarring: Moist wound treatment, by promoting the growth and movement of new cells and ensuring that proteins for closing the wound are efficient, causes reduced inflammation, promotes more even skin formation and therefore reduces scarring.
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3. The Importance of Moist Wound Healing
For the best wound care outcome and the quickest healing process, moist wound healing is the best choice. Today's wound care dressings have moisture management properties to fulfill all of the functions of the passive dressings of earlier times, but also promote faster healing, reduce pain, encourage vapor transmission, promote autolytic debridement, and also act as a bacterial barrier.
4. Moist dressings
Film dressings are semipermeable and transparent polymer membranes (most commonly made of polyurethane) that are coated with an adhesive. They maintain a moist environment by having reduced permeability to water. Semipermeable film dressings are commonly used to cover minor burns, STSG donor site wounds, postoperative wounds, and a variety of minor injuries, including abrasions and lacerations. There are multiple semipermeable films on the market that mainly differ in relationship to their moisture vapor transmission rate (MVTR). Tegaderm? and Opsite? are among the most commonly used film dressings.
Foam dressings are polymers, most commonly made of polyurethane, polyethylene, or silicone. The foams are designed to maintain a moist environment and absorb exudate from the wound. They usually consist of a hydrophobic permeable outer layer and a hydrophilic layer that is in direct contact with the wound bed. Typically, the foam dressings also contain a permeable polyurethane film with an adhesive that has a high MVTR and that is placed on the top of the foam and attaches the dressing to the peri wound skin. They are the most useful in moderate- to high-exuding wounds. Common foam dressings include Tegaderm Foam, LyofoamTM, AllevynTM, and MepilexTM.
NPWT dressings are also moist dressings. NPWT dressings are most commonly made of foam or gauze and covered with a semipermeable membrane. A tube that connects the space under the membrane to a suction pump is attached to the dressing. Negative pressure creates an environment that has a high humidity under the membrane. NPWT is used to promote and accelerate healing in all kinds of acute and chronic wounds. Common NPWT dressings include V.A.C? Therapy Dressings (foam), PrevenaTM (foam), and PicoTM (gauze).
Hydrocolloids are wound dressings comprising cross-linked matrix gelatin, pectin, and carboxymethyl cellulose sheets, powders, or pastes that together with adhesives usually are attached to a semipermeable film or foam. They maintain the moist environment by forming a gel with the wound fluid and maintaining their permeability. They are a good option for shallow and low-exuding wounds. Common hydrocolloid dressings include DuoDERM?, CombiDERMTM, and GranuGelTM.
Hydrogels are three-dimensionally cross-linked polymer networks composed of hydrophilic polymers (such as agarose, alginate, carboxymethyl cellulose, or collagen) with high water content. They are biocompatible, as they are structurally similar to the extracellular matrix. Hydrogels maintain the moist wound environment by delivering water molecules to the wound. They are used for many different types of wounds, including leg ulcers and pressure sores. Hydrogel dressings are available as amorphous (with no shape), impregnated into a secondary dressing such as gauze or foam and as sheets. Commonly used hydrogels include IntraSite? Gel, Purilon? Gel, and AquaSite? Hydrogel Sheet.
Alginate wound dressings are nonwoven and nonadhesive fibers that are produced from calcium and sodium salts of alginic acid. Alginic acid is composed of mannuronic and galuronic acid residues and their ratio affects the chemical and physical properties of the alginate. A high concentration of mannuronic acid promotes gelling and high galuronic acid concentration promotes fiber integrity. When in contact with wound exudates, alginates partly dissolve and form a hydrophilic gel that establishes a moist wound environment. The alginate dressings with high mannuronic acid content gel rapidly and are therefore called rapid gelling fiber dressings. Alginates are suitable for highly exuding wounds. Examples of alginate wound dressings include Algisite? and Kaltostat?.
There is no one dressing that fits all wound types. Moreover, as the healing of a wound progresses and the amount of exudate decreases, one single dressing may not be optimal for the different phases of healing. When choosing the best dressing for the wound, it is important to evaluate whether the wound is low or high exuding, condition of the peri wound area, location, wound size, and depth, as well as the risk/presence of infection. The following pages will discuss and compare the different functional characteristics of the moist dressings, such as MVTR, absorptive capacity, wear time, and antimicrobial properties .
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