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Management of Moisture

The aim of wound care is to provide the appropriate environment for healing by both direct and indirect methods, together with the prevention of skin breakdown. Dressings and topical agents are important aspects of the healing environment. They play a role in providing a moist environment absorbing excess exudates, lowering or removing wound bacteria, assisting in the removal of slough, and protecting the wound from contamination.

INTRODUCTION TO MOIST WOUND HEALING

Traditional wound care theory indicated that

  • Wounds should be kept clean and dry so that a scab can form over the wound.
  • Wounds should be exposed to the air and sunlight as much as possible.
  • When tissue loss is present, the wound should be packed to prevent surface closure before the cavity is filled.
  • Wounds should be covered with dry dressings.

The problem with the first of these principles is that the scab, which is made up of the dehydrated exudate and dead tissue, is a barrier to healing. Scabs delay healing by hindering the movement of epidermal cells; this can lead to poor cosmetic results and scarring. The second principle recommends exposure to air; however, this reduces the surface temperature of the wound, further delaying healing. Reduced surface temperature can also result in peripheral vasoconstriction, affecting the flow of blood, oxygen, nutrients, and other factors to the wound. Exposure to air will also increase fl uid loss and dry the wound surface. When a wound with tissue loss is packed with dry gauze, as recommended in the third principle, the quality of healing is impaired by the adhesion of the gauze to the surface of the wound. This causes the wound to dry out and increases the risk of trauma on removal of the packing (the limitations and appropriate use of gauze and other inert dressings are discussed shortly). Finally, in opposition to traditional beliefs, wounds should not be covered with dry dressings: doing so does not provide a moist environment essential for wound healing.

Benefits of Moist Dressings

Wounds managed in a moist environment covered by an occlusive dressing do not form a scab, so epidermal cells are able to move rapidly over the surface of the dermis through the exudate that collects at the wound-dressing interface.The application of a totally occlusive or semipermeable dressing to the wound can also prevent secondary damage as a result of dehydration. Moist wound healing also promotes autolytic debridement, the natural removal of slough and nonviable tissue by enhancing the action of enzymes released by the neutrophils of wound. It facilitates wound cleaning, since wound exudate is part of the healing cascade and has been shown to carry a number of growth factors essential to the healing of wounds. It also protects granulating tissue and encourages epithelialization. Dressings are used directly on the wound as the primary dressing or over the primary dressing to hold it in place or to help absorb exudate as a secondary dressing.

Limitation of Gauze dressing

Inert wound dressings are simple absorbent or nonabsorbing dressings that play no part in the wound environment other than exudate absorption and wound coverage. There are a number of drawbacks to the use of passive products, particularly gauze. First, because it’s a fibrous material, gauze tends to shed very readily and, as such, will contaminate the wound. Second, gauze is highly absorbent and, as a primary dressing, will tend to dry the surface of a wound rapidly. Third, gauze is permeable to bacteria, and moist gauze tends to be an environment that promotes bacterial growth. These bacteria can subsequently penetrate and ultimately contaminate the wound. Fourth, gauze is adherent and will traumatize the wound further on removal, risking pain and damage to granulating tissue.

Properties of an Ideal Dressing

The properties of an ideal dressing have been described as follows:

  • Will remove excessive exudates from the wound but will not allow the wound to dry out, maintaining a moist environment
  • Will allow gaseous exchange so that oxygen, water vapor, and carbon dioxide can pass into and out of the dressing
  • Will be thermally insulating, maintaining the wound core temperature at approximately 37°C
  • Will be impermeable to microorganisms, minimizing contamination from outside the wound
  • Will be free from either particulate or toxic contamination
  • Will be nontraumatic and will not adhere to the wound, so that no damage is done to granulating tissue on removal

In addition, the following properties should be considered when selecting the appropriate dressing:

  Will provide the proper environment for healing

  Will be user-friendly (to ensure compliance)

  Will have ease of application and removal

  Will simplify treatment (minimal changes of dressing)

  Will be cost-effective (i.e., total management cost)

  Will be compatible with the wound

  Will have minimal need for secondary dressings

  May be suitable for combined use with compression therapy

  May be used in infected wounds

  Will remain in place

INTERACTIVE WOUND DRESSINGS

Interactive wound dressings provide the wound environment for healing to take place. The term interactive is used because they are not passive but feature the ability to work actively with wound properties like wound fluid, tissue, cells, and growth factors within the wound to enhance healing. Thus, they provide an ideal wound environment for healing. Different dressing characteristics are exploited by choosing dressings based on the wound properties to be addressed. The various interactive dressings do have different properties and are classified  into six specific groups accordingly. For example, these dressings vary in their ability to absorb exudates: some have no ability to absorb, some will cope with low levels of exudates, and some are able to absorb large volumes of exudate.

The six types of interactive dressings are

  • Film dressings
  • Foam dressings
  • Hydrogel dressings
  • Hydrocolloid dressings
  • Alginate dressings
  • Hydroactive dressings.

Film Dressings

Film dressings are thin membranes coated with a layer of acrylic adhesive. They are moisture vapor-permeable and oxygen-permeable. One important difference in selecting a dressing is moisture vapor permeability. The moisture vapor permeability is measured with the moisture vapor permeability test. It should be noted that the loss of water vapor from intact skin is 240 to 1920 g/m2/24 hours, and the water vapor loss from an open wound is about 4800 g/m2/24 hours.

Although films are permeable to both oxygen and moisture vapor, they are impermeable to microorganisms and moisture. Thus, film dressings are flexible, elastic, extensible, and allow easy assessment of the wound because they are transparent. They are also impermeable to microorganisms. They do not have the ability to absorb any exudate.

Effects

The effects of film dressings include the following:

  • Provide a moist environment
  • Assist with autolytic debridement
  • Provide protection from chemicals, friction, shear, and microbes
  • Transmit oxygen into and carbon dioxide and water vapor out of the dressing
  • Function as a secondary dressing

Indications for Use

Film dressings are indicated in the management of minor burns and simple injuries (e.g., scalds, abrasions, and lacerations), and as a postoperative dressing over suture lines. They are also used as a protective layer over intravenous catheters, and for the prevention and treatment of superficial pressure areas. A film dressing enables autolytic debridement and provides a moist wound healing environment.

Indications for Discontinuation

An increased level of exudation that causes pooling under the dressing can lead to maceration of both the wound and the surrounding skin. The dressing should be discontinued in such cases. Use of the dressing should also be discontinued if the wound becomes clinically infected.

Method of Application

An appropriately sized piece of film should be chosen to cover the wound and provide an overlap of at least 4 to 5 cm from the edge of the wound. It is important to ensure that the skin around the wound is dry and free from oils or cream, because these may reduce adherence to the skin. Remove the bottom backing paper, and carefully apply the film dressing over the wound, while maintaining light but firm stretching of the edges of the fi lm to prevent it from sticking to itself. Once the dressing is in place, remove the upper cover. Film dressings are also used as a secondary dressing over hydrogels and alginates, as an alternative to tape for holding a dressing in place, and to provide a waterproof covering. In addition to standard fi lm dressings, island versions are now available, comprising a simple absorbent pad covered by the film. These products are able to absorb small amounts of wound exudate and can be used in wounds with low exudates.

Precautions and Contraindications

Film dressings may remain in place for up to 1 week or even longer. Changing of the dressing will depend on the position, type, and size of the wound. It is important to remove film dressings with care. Do not pull the dressing back across itself. Care should be exercised in applying fi lm dressings to damaged or frail skin and in those with fi ne and dry skin. Because of the risks of further damage on removal, the film should be carefully pulled away from itself while applying light pressure to the center of the fi lm dressing until it has been entirely removed.Film dressings are not recommended for use over  deep-cavity wounds, full-thickness burns, and wounds showing signs of clinical infection. They should be used only with caution in patients with damaged or frail skin and in those with fine and dry skin, because of the risks of skin damage on removal.

Foam Dressings

Foam dressings are produced from polyurethane as soft, open cell sheets, and can be composed of one layer or multiple layers. Foam dressings meet many of the standard requirements of the ideal dressing. They absorb exudate, thereby protecting the surrounding skin from maceration; raise the core temperature of the wound; and maintain a moist environment. Many polymer products are similar in appearance to foam dressings; however, these are hydroactive dressings or foam-like dressings that adsorb moisture into their structure and swell up. They are absorbent dressings, but they are not interchangeable with foam dressings in every situation. Foams are useful as both primary and secondary dressings.

Effects

The effects of foam dressings include the following:

  • Provide a moist environment
  • Provide high absorbency
  • Conform to body shape
  • Provide protection and cushioning
  • Produce no residue
  • Do not adhere to the wound
  • Provide thermal insulation
  • Transmit moisture vapor out of the dressing
  • Require no secondary dressings

Indications for Use

Foams are indicated for a wide range of minor and major wounds, including exuding wounds (both superficial and cavity types), leg ulcers, decubitus ulcers, and sutured wounds. They can be used over skin grafts, donor sites, and minor burns. They also may be used as secondary dressings over amorphous hydrogels. Foams improve the functioning of amorphous hydrogels by removing excess exudate from the wound and raising its core temperature. This assists with autolytic  debridement. Foams can also be used around tracheostomy tubes and other drainage tubes and catheters.

Method of Application

Place the foam dressing over the wound, allowing for a margin at least 3 to 4 cm greater than the size of the wound. Secure the dressing in place with one of the following:

  • In patients with fine or easily damaged skin:
  1. Lightweight cohesive bandage
  2. Tubular bandage
  • In other patients:
  1. Adhesive tape (hypoallergenic)
  2. Tubular or lightweight cohesive bandage

Foam dressings can be used under compression bandaging and as a secondary dressing for amorphous hydrogels and alginates. For a wound with a cavity, select the appropriately sized device to fit comfortably into the cavity and insert it into the wound. It may remain in place for 1 to 4 days or until saturated with exudate. A sheet foam dressing can remain in place for up to 7 days or until the exudate has saturated to the edge of the dressing.

Precautions

Foam dressings are of little value on dry wounds with a scab or eschar. They also should not be used alone in a dry cavity, but they may be used with an amorphous hydrogel. There are no specific contraindications for the use of foam dressings.

Expected Outcomes

Foam dressings provide a satisfactory primary and secondary dressing for a wide range of wounds. They aid in the removal of exudate, raise the core temperature of the wound, and protect the wound from external irritation. They will also protect the healthy skin around the wound from becoming macerated by the wound exudate.

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Hydrogels

Hydrogels are a group of complex organic polymers with high water content, from 30% to 90%. These broad classes of polymers are swollen extensively in water, but they do not  dissolve. They are three-dimensional, water-swollen, cross-linked  structures formed from hydrophilic homopolymers or copolymers. There are two types of hydrogels: amorphous and sheet. Amorphous hydrogels are nonfixed macrostructures that absorb water, progressively decreasing viscosity. They are free-flowing and will easily fill a cavity space. Sheet hydrogels are usually manufactured in the form of a thin, flexible sheet. These gels swell, increasing in size until the gel is saturated; they do not change their physical form as they absorb fluid.

Effects

Hydrogels provide moisture to dry wounds, but they are also able to absorb fl uid. They have the following useful effects:

  • Provide a moist environment
  • Aid in autolytic debridement
  • Conform to body shape
  • Do not adhere to the wound
  • Provide moisture and absorb moisture
  • Relieve pain

Indications for Use

Amorphous hydrogels are generally indicated for dry and sloughy wounds to rehydrate the eschar and enhance autolytic debridement. They are used on leg ulcers, pressure wounds, extravasation injuries, simple-thickness and partial-thickness burns, and infected wounds and necrotic wounds. They facilitate granulation and epithelialization by preventing the wound from drying out. Hydrogels are used to prevent the drying out of such tissue as tendon. Hydrogels are also a useful carrier of topical drugs to be applied to wounds, such as metronidazole and proteolytic enzymes. Amorphous hydrogels are also used for management of the lesions of chickenpox and shingles.

Indications for Discontinuation

Use of amorphous hydrogels should be discontinued if exudate from a wound is excessive. It is generally advised that the use of sheet hydrogels should be stopped if a wound is clinically infected.

Method of Application

Amorphous hydrogel should be applied to a wound to a minimum thickness of 5 mm and covered with a secondary dressing. The choice of secondary material depends on the type and position of the wound, as well as availability and cost. Foams are the most satisfactory secondary dressings, by virtue of their properties of exudate absorption, thus maintaining the integrity of the gel for a longer time, protecting the surrounding skin from maceration,and raising the core temperature to aid in autolysis. Otherproducts, such as film dressings, hydrocolloids, and simplenonadherent dressings, may be used. Gauze is also a suitable secondary dressing. Hydrogels can remain in place for a clean wound for up to 3 days; they should then be removed by irrigation with water or saline. When used for the lesions of chickenpox, they should be applied four or five times a day.Place sheet hydrogels over the wound with at least 3 to 4 cmcoverage greater than the wound. Hold the sheet in place withtape or a light cohesive bandage, depending on the skin of the patient.

Precautions and Contraindications

Because of their occlusive nature, sheet hydrogels should not be applied to clinically infected wounds unless the patient is taking systemic antibiotics. Amorphous hydrogels containing propylene glycol should not be used in patients known to be sensitive to propylene glycol. Sheet hydrogels should not be applied over small deep-cavity wounds. They should also not be used in heavily exuding wounds.

Expected Outcomes

Hydrogels aid in the rapid removal of necrotic tissue and rehydrate dry wounds, thereby assisting in granulation and reepithelialization. In burns, they reduce heat and pain. The thicker sheet hydrogels, when used in the management of superfcial pressure wounds, also reduce pressure by reducing friction and shear forces.

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Hydrocolloids

Hydrocolloid dressings are a combination of gel-forming polymers with adhesives held in a fi ne suspension on a backing of polyurethane fi lm or foam. The dressing mass contains, in most cases, sodium carboxymethyl cellulose (CMC) and other gel-forming agents, such as pectin, gelatin, and elastomers. These products are also available as granules, powder, and paste. When applied to an exuding wound, exudate combines with the polymers to form a soft gel mass in the wound. This gel will vary in viscosity, depending on the brand of dressing. The dressing does not adhere to the wound itself, only to the intact skin around the wound.

Effects

Hydrocolloids have the following effects:

  • Provide a moist environment
  • Aid in autolytic debridement of wounds
  • Conform to body shape
  • Protect from microbial contamination
  • Provide a waterproof surface
  • Require no secondary dressing

Indications for Use

Hydrocolloids are indicated in the management of superfcial leg ulcers, burns, donor sites (when hemostasis has been obtained), and pressure wounds. They may be used in smallcavity wounds, in combination with hydrocolloid paste, powder, or granules. Thin versions can be used as dressings over sutures after minor and major surgeries.

Indications for Discontinuation

Hydrocolloids should be discontinued on surface granulation of the wound or if hypergranulation occurs.

Method of Application

Hydrocolloids on a superficial wound should be applied to the wound with a margin of at least 3 to 4 cm greater than the wound size. The skin should be dry to ensure good adhesion, and it is preferable to place one-third of the dressing above the wound and two-thirds below the wound; this will prolong the wear time of the dressing. The dressing may remain in place for 5 to 7 days or until strikethrough has occurred (i.e., exudate has migrated to the outside edge of the dressing). Thnn, carefully remove the dressing and irrigate the wound with warm saline before applying a new dressing.In the case of small-cavity, relatively moist wounds, fill the cavity with hydrocolloid paste, powder, or granules and cover it with a sheet of hydrocolloid dressing. With a minimally to moderately exuding cavity, insert hydrocolloid paste carefully and then cover the wound with a sheet of hydrocolloid dressing. Change the dressing after 3 to 4 days. Irrigate the cavity with warm saline and gently remove any remaining product before applying the new dressing.Apply thin hydrocolloid dressings after surgical wound suturing. In most cases, these dressings can remain in place until removal of the sutures, clips, or Steri-Strip. For surgical wounds, these dressings have the advantage of being both flexible and waterproof. They require no secondary dressing, and help to appose wound edges by distributing tension at the suture line across the surface area of the dressing.

Precautions and Contraindications

When using these dressings on patients with thin and fragile skin, take care that the dressings do not cause further skin damage on removal. There are no absolute contraindications for use of hydrocolloids, but they are not indicated for use in heavily exuding wounds or in clinically infected wounds. They also are not considered suitable for deep-cavity wounds.

Expected Outcomes

Hydrocolloids help to remove necrotic tissue and slough from a wound and encourage angiogenesis and granulation of the wound. The presence of colonized bacteria in a wound does not contraindicate the use of these dressing

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Alginates

Alginates are the calcium or calcium/sodium salts of alginic acid and are composed of mannuronic and guluronic acids obtained from seaweed, primarily the genus Laminaria. They are available as a mixture of sodium alginate and calcium alginate in textile fiber sheets or as a loose packing ribbon. When applied to a wound, sodium ions present in the wound exchange for the calcium ions in the dressing, producing a hydrophilic gel and providing calcium ions to the wound. Since calcium acts as a clotting factor (factor IV), this mechanism enables some alginates to act as a hemostat. Sodium alginate has a complex structure consisting essentially of two uronic acids, D-mannuronic acid and L-guluronic acid. The ratio of these isomers varies, depending on the species of seaweed from which the alginate is extracted and the method of production. Gels that are rich in mannuronic acid form soft amorphous gels that partially dissolve or disperse in solutions containing sodium ions. Alginates that are rich in guluronic acid tend to swell in the presence of sodium ions, while retaining their basic structure.

Effects

Alginates have the following useful effects:

  • Provide a moist environment
  • Provide a high absorptive capacity
  • Conform to body shape
  • Protect from microbial contamination
  • Provide hemostasis
  • Do not adhere to the wound

Indications for Use

Alginates are used in exuding wounds, such as leg ulcers, cavity wounds, and pressure wounds, and at donor sites (as a hemostat postsurgically) and other bleeding sites. They may be used in infected wounds.

Indications for Discontinuation

Alginates should be discontinued if the amount of exudate is insufficient to cause the fiber to gel. They should not be premoistened with saline to promote gelling.

Method of Application

Sheet alginates should be placed in and conformed to the shape of the wound, and covered with a secondary dressing, such as a foam, or a nonadherent dressing. Depending on the  condition of the patient’s skin, the sheets can be held in place with tape or a light cohesive bandage. If the wound is extremely  exudative, add an extra covering with a simple absorbent pad. In the case of a cavity wound, gently place rope or packing  alginate material in the cavity, taking care not to pack the material tightly into the space. When used on a donor site, apply the sheet alginate to the donor area after skin harvesting and cover it with a film dressing or foam. This aids in rapid hemostasis and provides an environment conducive to reepithelialization of the skin. In general, the dressing should remain in place in clean wounds for no longer than 7 days or until the gel loses its viscosity (this will vary, depending on the level of exudation from the wound). Change dressings on clinically infected wounds daily. Remove the alginate by simple irrigation of the wound or cavity with warm saline. Freeze-dried alginates may be applied not only to the wound but also to cover the periwound skin because they gel only over the wound, thus protecting the periwound skin from maceration.

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Precautions and Contraindications

For clinically infected wounds, the dressing should be changed daily and the concurrent use of systemic antibiotics is typically necessary. There are no known contraindications for the use of alginates; however, they are not suitable for use in dry wounds or in wounds with thick, black eschar.

Expected Outcomes

Alginates absorb exudate and provide a moist environment for granulation. They are suitable for use in infected wounds and are very effective in the management of bleeding, particularly in postnasal surgery, post biopsy, and when applied to donor sites. They provide a comfortable dressing, and rapid healing of the skin is expected. Alginate dressings have known hemostatic properties: factors such as wound type, position, and depth will determine the best dressing to apply over a bleeding wound.

Silicone

Silicone is a manufactured polymer that includes the element silicon. Dressings containing silicone are used to reduce hypertrophic and some keloid scars. These dressings should be applied as soon as possible after sutures or clips are removed from the incision site. They are changed every 1 to 3 days, after which the area is washed and the dressing is reapplied. The same piece of dressing may be used for about 7 days, and then a fresh piece is applied.Silicone is also used as the surface layer on a number of other types of dressings including tulles and foam dressings. The silicone helps maintain adhesion of the dressing onto the skin; however, silicone does not stick and thus allows nontraumatic removal. The dressing also reduces pain at the wound interface and on removal of the dressing.

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Secondary Dressings

The choice of secondary dressing depends on the nature, position, and level of exudate. In general terms, film dressings and nonadherent dressings are suitable for lightly exuding wounds, but not for high levels of exudation. Foam dressings are useful over amorphous hydrogels and alginates (this does not apply to the foam-like hydroactive dressings). The use of gauze as a secondary dressing is limited, especially over hydrogels or alginates, because it reduces the ability of the dressing to function at its optimum level.Another important consideration is the method of dressing retention. If the surrounding skin is healthy, the dressing can be held in place with high-quality tape. If the skin is dry, thin, fragile, or otherwise poor, a tubular bandage or a lightweight cohesive bandage is suitable.