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Wound Dressings



One Medical Dictionary defines a Wound Dressing this way, “any material used for covering and protecting a wound.” That maybe an over generalization but nevertheless it is accurate. Many define a wound dressing as a material (liquid or otherwise) that comes in direct contact with a wound, which would distinguish it from a bandage which is designed to hold a dressing securely in place.

Why is dressing a wound so important?

Rapid covering and healing of both acute skin defects and chronic skin defects are important objectives for wound healing. The best way to heal a wound is to close it according to surgical standards as quickly as possible after injury. However, this procedure is limited to those wounds and those anatomical regions that allow both excision and adaptation of wound borders to close the wound by primary intention or per primam (Latin term meaning to close the wound by suturing [or equivalent method] and restructuring of the skin continuity).

In large-surface and deep wounds in which the primary wound closure is not possible or not practicable, the most important issue is to dress the wound with appropriate materials to allow the following:

  • to keep the wound free of infection
  • to reduce or eliminate pain
  • to reduce or eliminate all potential factors inhibiting natural healing (eg, dead tissue in burns, superficial fibrosis, necrotic tissue), and
  • to replace or substitute the missing tissue as much as possible.

What are my choices?

Below is a non-exhaustive list of Wound Dressing Materials and products available in the US Market

Wound Dressings - Material Categories

What’s best for me?

The ideal wound dressing should have the following characteristics:

  • Provide mechanical and bacterial protection
  • Maintain a moist environment at the wound/dressing interface
  • Allow gaseous and fluid exchange
  • Remain nonadherent to the wound
  • Safe in use - Nontoxic, nonsensitizing, and nonallergic (both to the patient and the medical personnel)
  • Well acceptable to the patient (eg, providing pain relief and not influencing movement)
  • Highly absorbable (for exuding wounds)
  • Absorb wound odor
  • Sterile
  • Easy to use (can be applied by medical personnel or the patient)
  • Require infrequent changing (if necessary)
  • Available in a suitable range of forms and sizes

Classic dressings (not all categories are discussed in this article) include dry dressings and moisture-keeping dressings. Dry dressings include gauze and bandages, nonadhesive meshes, membranes and foils, foams, and tissue adhesives.

Moisture-keeping dressings include pastes, creams and ointments, nonpermeable or semipermeable membranes or foils, hydrocolloids, hydrogels, and combination products.

Bioactive dressings include antimicrobial dressings, interactive dressings, single-component biologic dressings, and combination products.

Skin substitutes include epidermal substitutes (autologous or allogenic), acellular skin (dermis) substitutes (allogenic or xenogenic), autologous and allogenic skin, and skin substitutes containing living cells.

Different types of wounds require different dressings or combinations of dressings.

Synthetic or semisynthetic dressings

Silicones

Silicone dressings consist of chemically and biologically inert, usually transparent, silicon sheets or gels. Some of the silicone membranes are porous to allow gas and moisture exchange between the wound surface and the environment. Other silicone membranes are nonpermeable to ensure a fully occlusive wound environment.

Barrier films

Barrier films are protective polymers dissolved in a fast-drying carrier solvent, which, ideally, should be noncytotoxic, be pain reducing on application to broken skin, protect skin from loosing moisture or from exogenic fluids, protect from skin stripping, and be compatible with clothing. Such dressings may be applied as fluids, which quickly polymerize on the wound surface or as industrially prepared membranes made mostly from polyurethane or polylactate.

Foams

Foams mostly consist of polyurethane porous sponges or polyurethane foam films with or without adhesive borders. Most of them are suitable for use on light-to-medium exuding wounds. Many types of foams may be left on the wound surface for up to 7 days, depending on exudate volume. Foams are not recommended for any kind of dry wounds. Besides the usual range of sizes, anatomically shaped dressings are available for specific wound locations (eg, sacral region, heel).

Tissue adhesives

Tissue adhesives have been developed to exchange suturing in some, mostly small and not-too-deep wounds that can heal by primary intention. Moreover, such products may be used in the form of surface covering liquid bandages.

Currently used tissue adhesives contain cyanoacrylate components, including bucrylate, enbucrilate, and mecrylate, which polymerize in an exothermic reaction on contact with either a fluid or a basic substance. Such a process leads to the forming of a strong, flexible, waterproof band.

Tissue adhesives are used for simple lacerations, which otherwise might require the use of fine sutures, staples, or skin strips, producing cosmetic results similar or better than traditional suturing. This is a needless and mostly painless method of wound repair that does not require follow-up visits for suture removal.

Tissue adhesives provide the strength of healed tissue seen at 7 days. Special attention is necessary to ensure that wound edges are appropriately adapted and that no adhesive passes between wound borders.

Hydrogels

Hydrogel dressings contain a large portion of water, often more than 70-90%. They have some important characteristics of an ideal dressing. Hydrogels can cool the surface of the wound, resulting in marked pain reduction.

Moreover, hydrogels maintain the moist wound environment and are mostly suitable for use on dry or necrotic wounds or on lightly exuding wounds. They are suitable for use at all stages of wound healing except for infected or heavily exuding wounds. Hydrogels are a good alternative for classic wet dressings.

In some cases, however, hydrogels may macerate the healthy skin (mostly wound border areas), decreasing the keratinocyte reepithelialization ratio or leading to overwetting of split-skin donor sites. Hydrogels are available as sheet dressings or gels.

Hydrocolloids

Hydrocolloid dressings are much more complicated than hydrogels because they contain a variety of constituents, such as methylcellulose, pectin, gelatin, and polyisobutylene. Some of them also contain alginate. After contact with the wound surface, hydrocolloids slowly absorb fluids, leading to a change in the physical state of the dressing and to the formation of gel covering the wound. Thus, they are called interactive dressings.

Hydrocolloids ensure the moist wound environment, promote the formation of granulation tissue, and provide pain relief by covering nerve endings with both gel and exudate. These dressings are marketed with or without adhesive borders. Depending on the choice of product, hydrocolloids are suitable for the dressing of both acute wounds and chronic wounds, for desloughing, and for different stages of light-to-heavily exuding wounds.

Initially, hydrocolloid wound dressings need to be changed daily (depending of the exudate level), but, once the exudate has diminished, dressings may be left on the wound surface for up to 7 days. With a few exceptions, hydrocolloids require a secondary dressing to be fixed in place. Hydrocolloids should not be used on infected wounds.

Calcium alginates

Alginates are highly absorbable biodegradable dressings derived from seaweed (eg, Kaltostat, Tegagen, SorbSan, SeaSorb, Algisite M, Algosteril). They contain the building blocks of mannuronic acid (M) and glucuronic acid (G). The high M alginates are soft and gel-like, whereas the high G alginates are more stable and ribbon- or rope-like.

Large quantities of alginates are used each year to treat exudating wounds, such as leg ulcers, pressure sores, and infected surgical wounds. In addition to controlling exudate by ion exchange, alginates are believed to exert a bioactive effect by activating macrophages within the chronic wound bed to generate proinflammatory signals (eg, tumor necrosis factor-alpha [TNF-alpha], interleukin 1, interleukin 6 [IL-6], interleukin 12).

This may then initiate a resolving inflammatory response characteristic of healing wounds. Chronic wounds are now well known to be characterized by macrophage-rich inflammation, and any putative macrophage defects probably relate to the functional status of the macrophages present at the wound site.

In vitro studies have demonstrated that some dressings containing alginates can activate macrophages, as evidenced by their increased production of TNF-alpha. Research is currently underway to modulate alginate dressings to enhance these effects and to incorporate antimicrobial silver into alginate preparations (eg, Acticoat Absorbent). In addition, new preparations (eg, AGA-100) that have a reduced cytotoxicity to cells, such as fibroblasts, compared with both Kaltostat and Sorbsan, are being developed.

Alginates are not the dressing of choice for infected wounds and should not be applied to dry or drying wounds. Most alginates require a secondary dressing.

Dressings containing an antimicrobial agent

An important consideration in the design of new dressings is their ability to combat microbial infection. Many dressings now exploit bioactive properties to promote healing and to control infection.

These dressings include the now well-known sustained-release iodine and silver dressings (eg, Iodosorb, Actisorb Silver 220). Silver metal and its salts have been used for several generations under many different formulations (eg, ointments, pulvers, foams, films). Possible reasons for the antimicrobial effect of silver include

  • interference with bacterial electron and ion transport
  • binding to bacterial DNA, which may impair cell replication
  • interaction with cell membrane, which may damage its structural and receptor function; and
  • formation of insoluble and metabolically ineffective compounds.

The ideal silver dressing will contain a concentration of silver to exert an effective antibacterial effect without or with only limited systemic absorption. However, locally applied silver compounds may react with wound fluid and form black silver sulphide, giving the skin a gray discoloration. The use of silver nitrate solution is more likely to cause this phenomenon than modern silver dressings.

Conclusion

Many different materials are available to dress both acute wounds and chronic wounds. Given the importance of proper wound care, communication with your health care professional is critically important.




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