Standing Height

Standing Height

description / procedure: measurement the maximum distance from the floor to the highest point on the head, when the subject is facing directly ahead. Shoes should be off, feet together, and arms by the sides. Heels, buttocks and upper back should also be in contact with the wall.

equipment required: stadiometer or steel ruler placed against a wall

reliability: Height measurement can vary throughout the day, being higher in the morning, so it should be measured at the same time of day each time.

advantages: low costs, quick test

other comments: height or lack of height is an important attribute for many sports.

Related Pages

see similar test: sitting height

other Anthropometric Tests

about body size testing Body Mass / Weight

purpose: measuring body mass can be valuable for monitoring body fat or muscle mass changes, or for monitoring hydration level.

equipment required: Scales, which should be calibrated for accuracy using weights authenticated by a government department of weights and measures.

description / procedure: the person stands with minimal movement with hands by their side. Shoes and excess clothing should be removed.

reliability: To improve reliability, weigh routinely in the morning (12 hours since eating). Body weight can be affected by fluid in the bladder (weigh after voiding the bladder). Other factors to consider are the amount of food recently eaten, hydration level, the amount of waste recently expelled from the body, recent exercise and clothing. If you are monitoring changes in body mass, try and weigh at the same time of day, under the same conditions, and preferably with no clothes on. Always compare using the same set of scales.

advantages: quick and easy measurement when testing large groups, with minimal costs.

other comments: measuring weight can be used as a measure of changes in body fat, but as it does not take into account changes in lean body mass it is better to use other methods of body composition measurement.

Related Pages

other Anthropometric Tests

about body size testing Wound Care Introduction

A wound is a break in the skin (the outer layer of skin is called the epidermis). Wounds are usually caused by cuts or scrapes. Different kinds of wounds may be treated differently from one another, depending upon how they happened and how serious they are.

Healing is a response to the injury that sets into motion a sequence of events. With the exception of bone, all tissues heal with some scarring. The object of proper care is to minimize the possibility of infection and scarring.

There are basically 4 phases to the healing process:

Inflammatory phase: The inflammatory phase begins with the injury itself. Here you have bleeding, immediate narrowing of the blood vessels, clot formation, and release of various chemical substances into the wound that will begin the healing process. Specialized cells clear the wound of debris over the course of several days.

Proliferative phase: Next is the proliferative phase in which a matrix or latticework of cells forms. On this matrix, new skin cells and blood vessels will form. It is the new small blood vessels (known as capillaries) that give a healing wound its pink or purple-red appearance. These new blood vessels will supply the rebuilding cells with oxygen and nutrients to sustain the growth of the new cells and support the production of proteins (primarily collagen). The collagen acts as the framework upon which the new tissues build. Collagen is the dominant substance in the final scar.

Remodeling phase: This begins after 2-3 weeks. The framework (collagen) becomes more organized making the tissue stronger. The blood vessel density becomes less, and the wound begins to lose its pinkish color. Over the course of 6 months, the area increases in strength, eventually reaching 70% of the strength of uninjured skin.

Epithelialization: This is the process of laying down new skin, or epithelial, cells. The skin forms a protective barrier between the outer environment and the body. Its primary purpose is to protect against excessive water loss and bacteria. Reconstruction of this layer begins within a few hours of the injury and is complete within 24-48 hours in a clean, sutured (stitched) wound. Open wounds may take 7-10 days because the inflammatory process is prolonged, which contributes to scarring. Scarring occurs when the injury extends beyond the deep layer of the skin (into the dermis).

Synthetic wound dressings

Synthetic wound dressings originally consisted of two types; gauze-based dressings and paste bandages such as zinc paste bandages. In the mid-1980s the first modern wound dressings were introduced which delivered important characteristics of an ideal wound dressing: moisture keeping and absorbing (e.g. polyurethane foams, hydrocolloids) and moisture keeping and antibacterial (e.g. iodine-containing gels).

During the mid 1990s, synthetic wound dressings expanded into the following groups of products:

vapour-permeable adhesive films

hydrogels

hydrocolloids

alginates

synthetic foam dressings

silicone meshes

tissue adhesives

barrier films

silver- or collagen-containing dressings

Silver containing dressings

Ideal wound dressing

No single dressing is suitable for all types of wounds. Often a number of different types of dressings will be used during the healing process of a single wound. Dressings should perform one or more of the following functions:

Maintain a moist environment at the wound/dressing interface

Absorb excess exudate without leakage to the surface of the dressing

Provide thermal insulation and mechanical protection

Provide bacterial protection

Allow gaseous and fluid exchange

Absorb wound odour

Be non-adherent to the wound and easily removed without trauma

Provide some debridement action (remove dead tissue and/or foreign particles)

Be non-toxic, non-allergenic and non-sensitising (to both patient and medical staff)

Sterile

Classification of wound dressings

Synthetic wound dressings can be broadly categorized into the following types.

Type Properties

Passive products Traditional dressings that provide cover over the wound, e.g. gauze and tulle dressings

Interactive products Polymeric films and forms which are mostly transparent, permeable to water vapour and oxygen, non-permeable to bacteria, e.g. hyaluronic acid, hydrogels, foam dressings

Bioactive products Dressings which deliver substances active in wound healing, e.g. hydrocolloids, alginates, collagens, chitosan

Wound types and dressings

The following table describes some of the many different types of wound dressings and their main properties.

Dressing type Properties

Gauze Dressings can stick to the wound surface and disrupt the wound bed when removed

Only use on minor wounds or as secondary dressings

Tulle Dressing does not stick to wound surface

Suitable for flat, shallow wound

Useful in patient with sensitive skin

E.g. Jelonet, Paranet

Semipermeable film Sterile sheet of polyurethane coated with acrylic adhesive

Transparent allowing wound checks

Suitable for shallow wound with low exudate

E.g. OpSite, Tegaderm

Hydrocolloids Composed of carboxymethylcellulose, gelatin, pectin, elastomers and adhesives that turn into a gel when exudate is absorbed. This creates a warm, moist environment that promotes debridement and healing

Depending on the hydrocolloid dressing chosen can be used in wounds with light to heavy exudate, sloughing or granulating wounds

Available in many forms (adhesive or non-adhesive pad, paste, powder) but most commonly as self-adhesive pads

E.g. DuoDERM, Tegasorb

Hydrogels Composed mainly of water in a complex network or fibres that keep the polymer gel intact. Water is released to keep the wound moist

Used for necrotic or sloughy wound beds to rehydrate and remove dead tissue. Do not use for moderate to heavily exudating wounds

E.g. Tegagel, Intrasite

Alginates Composed of calcium alginate (a seaweed component). When in contact with wound, calcium in the dressing is exchanged with sodium from wound fluid and this turns dressing into a gel that maintains a moist wound environment

Good for exudating wounds and helps in debridement of sloughing wounds

Do not use on low exudating wounds as this will cause dryness and scabbing

Dressing should be changed daily

E.g. Kaltostat, Sorbsan

Polyurethane or silicone foams Designed to absorb large amounts of exudates

Maintain a moist wound environment but are not as useful as alginates or hydrocolloids for debridement

Do not use on low exudating wounds as this will cause dryness and scabbing

E.g. Allevyn, Lyofoam

Hydrofibre Soft non-woven pad or ribbon dressing made from sodium carboxymethylcellulose fibres

Interact with wound drainage to form a soft gel

Absorb exudate and provide a moist environment in a deep wound that needs packing

Collagens Dressings come in pads, gels or particles

Promote the deposit of newly formed collagen in the wound bed

Absorb exudate and provide a moist environment

Different types of wounds and the different stages of a healing wound require different dressings or combinations of dressings. The following table shows suitable dressings for particular wound types.

Wound type Dressing type

Clean, medium-to-high exudate (epithelialising) Paraffin gauze

Knitted viscose primary dressing

Clean, dry, low exudate (epithelialising) Absorbent perforated plastic film-faced dressing

Vapour-permeable adhesive film dressing

Clean, exudating (granulating) Hydrocolloids

Foams

Alginates

Slough-covered Hydrocolloids

Hydrogels

Dry, necrotic Hydrocolloids

Hydrogels

The dressings may require secondary dressings such as absorbent pad and bandages.

Adverse effects of dressings

Wound dressings can cause problems, including:

Maceration (sogginess) of surrounding skin (change dressing frequently and use a more absorbent dressing)

Irritant contact dermatitis (protect skin with emollient or barrier film)

Allergic contact dermatitis (uncommon: change dressing type, apply topical steroids)

Wound repairWound repair involves the timed and balanced activity of inflammatory, vascular, connective tissue, and epithelial cells. All of these components need an extracellular matrix to balance the healing process. Skin wounds heal by the formation of epithelialized scars of different contraction ability rather than by the regeneration of a true full-thickness tissue. To minimize scar formation and to accelerate healing time, different wound dressings and different techniques of skin substitution have been introduced in the last decades.

Autologous skin grafting in the form of split- or full-thickness skin is still a criterion standard. However, in many patients, this technique may not be practicable for a variety of reasons, and the wound must be allowed to heal by second intention. Moreover, in cases in which skin grafts are used, a new wound is created on the donor side. Thus, eliminating a new wound to close the old one and to close as many tissue defects as possible without the risk of large area infection, necrosis, tissue hypertrophy, and contraction, as well as deformation of wound borders, is a necessity. The next important problem is to reduce or eliminate scar formation, particularly in the field of large-surface wounds.

Traditional management of large-surface or deep wounds involves open and closed methods. In the open method, the wounds are left in a warm, dry environment to crust over, whereas, in the closed method, wounds are covered with different kinds of temporary dressings and topical treatment, including antibiotics, until healing by secondary intention. The early removal of the dead tissue (eg, in burns) reduced pain, the number of surgical procedures, and the length of the hospital stay.

The surgical intervention (ie, tangential excision of partial- or full-thickness wound) followed by wound closure with autografts or temporary dressings is one of the currently used methods. In large-surface, full-thickness wounds, the wound can be excised down to the fat or the fascia, particularly if infection is present. Excision to the fat induces the removal of the subdermal plexus of blood vessels and decreases the take of autografts because this tissue is less vascularized. Excision down to the fascia induces better take of the autografts but has aesthetic disadvantages.

Wound debridement can also be achieved by enzyme digestion of the dead tissues. Proteolytic enzymes (eg, collagenases used topically) allow a more specific destruction of necrotic tissues, while preserving viable dermis and avoiding blood loss, but the treatment can be painful and can increase the risk of local infection. In addition, it takes a long time to achieve a clean wound bed.

Wound coveringsCurrently available wound coverings can be divided into 2 categories: (1) permanent coverings, such as autografts, and (2) temporary coverings, such as allografts (including de-epidermized cadaver skin and in vitro reconstructed epidermal sheets), xenografts (ie, conserved pig skin), and synthetic dressings.

Conventional autograft (epidermis and a significant amount of dermis) obtained from healthy skin areas is considered the optimum wound cover in that its viability yields immediate take (incorporation into the wound bed) and resistance to wound infection. However, harvesting of autograft creates a second wound in the healthy tissue, a donor wound. This open wound increases the risk of infection and fluid/electrolyte imbalance. Repeated conventional harvests of autograft from a donor wound site can result in contour defects or scarring. Optimizing the healing of both main wounds and donor wounds becomes a later goal of patient management and the development of different surgical dressings, which can be used based on the principle of phase-adapted wound healing.

Most recently, developed wound dressings are in use only as temporary dressings because of their synthetic or chemical components, limited persistence on the wound surface, and foreign body character.

Primary closure versus second-intention treatment of skin punch biopsy sites was evaluated in a randomized trial.1 Punch biopsy sites healed by second intention appear at least as good as biopsy sites closed primarily with sutures. Volunteers preferred suturing for 8-mm biopsy sites and had no preference for 4-mm sites. Elimination of suturing of punch biopsy wounds results in personnel efficiency and economic savings for both patients and medical institutions.

The wounds had been dressed with petroleum jelly under an occlusive dressing that consisted of gauze covered by a transparent dressing (Tegaderm; 3M, St Paul, Minn) and were left in place for 3 days. After that time, the gel foam was removed from the second-intention site and both biopsy sites were cleansed with water to remove any exudate. Then, an occlusive transparent dressing was reapplied to both sites. After this initial dressing change, dressings were changed weekly or more often at the volunteers' discretion until the biopsy sites were completely healed or reepithelialized. Efficient wound dressings can be important for both small and large wounds.

Some of the currently available surgical dressings used in dermatologic and dermatosurgical practice are discussed.

CLASSIFICATION OF WOUNDS

Section 3 of 10

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Authors and Editors

Introduction

Classification of Wounds

Wound Bed Preparation

Autologous and Allogenic Skin Replacement

Types of Dressings

Acellular Dressings and Skin Substitutes

Engineered Skin Dressings and Substitutes

Perspectives

References

Wounds encountered in surgical and dermatosurgical practice can be classified according to their thickness, the involvement of skin or other structures, the time elapsing from the trauma (breaking of skin continuity), and their morphology. Additional classifications include factors that determine how to close the wound, classification of how the wound heals, and classification of the wound by bacterial contamination.

Thickness of the wound Superficial wounds, involving only the epidermis and the dermis up to the dermal papillae

Partial-thickness wounds, involving skin loss up to the lower dermis (Part of the skin remains, and shafts of hair follicles and sweat glands are leftover.)

Full-thickness wounds, involving the skin and the subcutaneous tissue (Tissue loss occurs, and the skin edges are spaced out.)

Deep wounds, including complicated wounds (eg, with laceration of blood vessels and nerves), wounds penetrating into natural cavities, and wounds penetrating into an organ or tissue

Involvement of other structures Simple wounds, comprising only 1 organ or tissue

Combined wounds (eg, in mixed tissue trauma)

Time elapsing from the trauma Fresh wounds, up to 8 hours from the trauma

Old wounds, after 8 hours from trauma or skin discontinuity

Morphology Excoriation or scarification, the most superficial type

Incised wound, mainly as a result of surgical intervention

Crush wound, made with a heavy blow of a cutting tool (eg, hatchet, sword, sable)

Contused wound, the most common type of wound encountered in traffic accidents

Lacerated wound, when fragments of tissue are torn away with a sharp-edged object

Slicing wound (A classic example is detachment of epicranial epineurosis.)

Stab wound, made with a pointed tool or a weapon

Bullet wound

Bite wound

Poisoned wound

Factors that determine how to close the wound Type of wound

Size of wound

Location of wound (Poor vascular areas or areas under tension heal slower than areas that are highly vascular.)

Age of wound (fresh surgical wounds vs chronic wounds)

Presence of wound contamination or infection (Bacterial contamination slows down the healing process.)

Age of the patient (The older the patient, the slower the wound heals.)

General condition of the patient (Malnutrition slows down the healing process.)

Medication (Anti-inflammatory drugs may slow down the healing process if they are taken after the first several days of healing. After this period, anti-inflammatory drugs should not have an effect on the healing process.)

Classification of how the wound heals Healing by first (primary) intention (primary healing): The wound is surgically closed by reconstruction of the skin continuity by simple suturing, by movement (relocation) of skin fragments from the surrounding area (flaps), or by transplantation of free skin elements (grafts) of different thickness (eg, split- or full-thickness grafts). Primary healing is usually the case in all wounds in which the anatomical location and the size allow the skin continuity to be restored.

Healing by second intention (secondary wound healing): After wound debridement and preparation, the wound is left open to achieve sufficient granulation for spontaneous closure (reepithelialization from remaining dermal elements [eg, hair follicle] or from wound borders). Secondary healing is how abrasions or split-thickness graft donor sites heal.

Healing by third intention (tertiary wound healing [delayed primary closure]): After wound debridement and preparation (ie, treatment of local infection), the wound is left open and then closed by primary intention or finally by surgical means of skin grafting. Tertiary healing is how primary contaminated wounds or mixed tissue trauma wounds (eg, after reconstruction of hard tissue) heal.

Classification of wound by bacterial contaminationThe 4 types of surgical wounds are as follows: clean, clean contaminated, contaminated, and dirty.

Clean wounds are usually wounds made by the doctor during an operation or under sterile conditions. Only normally present skin bacteria are detectable.

In clean-contaminated wounds, the contamination of clean wounds is endogenous and comes from the environment, the surgical team, or the patient's skin surrounding the wound.

In contaminated wounds, large contaminates infect the wound.

In dirty wounds, the contamination comes from the established infection.

In the daily praxis, the main objective for dermatologists, dermatosurgeons, and surgeons is to transfer the wound from a spontaneous stage to a surgical stage and to heal the wound by primary intention. However, this is not always possible or practicable. In such cases, wounds heal mostly by secondary intention, and the injured tissue becomes healthy again; appropriate wound dressings are necessary to give the wound an optimal environment to heal.

WOUND BED PREPARATION

Section 4 of 10

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HYPERLINK "http://www.emedicine.com/derm/fulltopic/topic826.htm" \l "section~AutologousandAllogenicSkinReplacement"

Authors and Editors

Introduction

Classification of Wounds

Wound Bed Preparation

Autologous and Allogenic Skin Replacement

Types of Dressings

Acellular Dressings and Skin Substitutes

Engineered Skin Dressings and Substitutes

Perspectives

References

Before any kind of wound dressing is applied, the wound should be appropriately prepared to enhance both the effectiveness of the dressing and the self-healing ability of the wound. To achieve optimal healing, wounds must not be infected, they should contain as much vascularized wound bed as possible, and they should be free of exudate.

Wound bed preparation in both acute wounds and chronic wounds is currently a part of the overall wound healing cascade, including (1) local blood coagulation, (2) vascular supply, (3) inflammation, (4) granulation tissue formation and revascularization, (5) epithelialization, (6) wound contraction, and (7) scar formation. However, the way of wound bed preparation in acute wounds differs from that of chronic wounds. For example, in acute wounds, debridement is an effective way to remove both damaged tissue and potential bacteria. Once performed, the acute wound should be clean and prepared to heal easily by primary intention. However, in the case of chronic wounds, debridement is usually an ongoing process.

Unlike acute wounds, chronic wounds have what is termed necrotic burden consisting of nonviable tissue and exudate. This is usually a result of many, mostly long-standing local or systemic abnormalities, such as diabetes, arterial or venous insufficiency, and local tissue compression, leading pathogenetically to chronic wounds.

Drs Falanga2, Sibbald, and Harding introduced the concept of wound bed preparation in the late 1990s. Wound bed preparation is defined as the global management of the wound to accelerate endogenous healing or to facilitate the effectiveness of other therapeutic measures, including wound debridement, bacterial balance, and moisture balance. This concept leads to more effective strategies to address the reasons why chronic wounds fail to heal. Wound bed preparation as a strategy allows physicians to break into individual components in various aspects of wound care, while maintaining a global view of what they wish to achieve.

Chronic wounds have always been overshadowed by acute wounds. Scientific breakthroughs and therapeutic measures would generally be developed or envisioned first for wounds caused by trauma, scalpel, or other types of acute injury. For instance, stimulation of reepithelialization by dressings providing moist conditions was first observed experimentally in acute wounds. The acceleration of healing by peptide growth factors was first formally demonstrated in experimental acute wounds in animals. These observations provided proof of principle for the effectiveness of topically applied growth factors, and they led to testing and commercialization of these agents in chronic wounds. Many other examples exist, but the point is that knowledge accumulated about acute injury has been the anchor on which one has relied for developing a therapeutic strategy for chronic wounds.

The common error is to view wound bed preparation as the same as wound debridement. In acute wounds, wound debridement is a good way to remove necrotic tissue and bacteria. This is not the case for chronic wounds, where much more than debridement needs to be addressed for optimal results. Chronic wounds can be intensely inflammatory (eg, venous ulcers) and, thus, produce substantial amounts of exudate that interfere with healing or with the effectiveness of therapeutic products, such as dressings, growth factors, and bioengineered skin substitutes. Therefore, in the context of wound bed preparation, the concerns are not only the removal of actual eschars and frankly nonviable tissue but also the removal of the exudative component.

Another important aspect of chronic wounds, which make them different from acute wounds in the context of wound bed preparation, is the possible need for a maintenance debridement phase. Debridement, whether it is performed by surgical, enzymatic, or autolytic means, is usually considered a procedure or a therapeutic step with defined time frames. This may be true of acute wounds that have become colonized and necrotic and, thus, need to be revitalized. However, with chronic wounds, debridement is generally unable to fully remove the underlying pathogenic abnormalities; necrotic material, nonviable tissue, and exudate (ie, necrotic burden) continue to accumulate.

Within the context of wound bed preparation, the notion of an initial debridement phase followed by a maintenance debridement phase may be adopted. For example, after the initial debridement of chronic wounds, a temporary positive outcome on wound closure may be observed. However, often, a healing arrest occurs, with a return to a poor wound bed. One explanation may be that, because of the underlying and uncorrected pathogenic abnormalities, necrotic tissue and exudate, which now cause the healing arrest, continue to accumulate. Rather than always starting from the beginning, with periodic debridement and exudate control, one might consider a steady state removal of the necrotic burden that should continue throughout the life of the wound.

In the concept of wound bed preparation, the biologic microenvironment of chronic wounds has to be clearly understood. For example, after an appropriate dressing is used, optimal compression therapy for edema control in venous ulcers decreases the amount of exudate and, thus, clears the macromolecules that may be trapping growth factors. Similarly, correction of the bacterial burden decreases the possibility of infection, but it also diminishes the ongoing inflammation that often characterizes many chronic wounds. Some chronic wounds may be "stuck" in one of the phases of the normal healing process, such as the inflammatory or proliferative phase. Eliminating the bacterial burden by the use of debridement, some antibacterial products, or adequate dressings can help this situation.

As another example, appropriate debridement removes tissue and, therefore, cells that have accumulated and are no longer responsive to signals required for optimal wound healing. In this respect, fibroblasts from chronic wounds, including venous and diabetic ulcers, have been shown to become senescent and are unresponsive to certain growth factors. The term cellular burden has been created to describe this phenomenon. When a wound is debrided, this cellular burden is removed and wound responsiveness is restored. In the future, some specially developed chemical or biologic agents will probably help for normalizing such cells rather than removing them.

In aiming at a well-vascularized wound bed, much can be achieved by removing necrotic or fibrinous tissue, by controlling edema, by decreasing bacterial burden, by performing compression therapy (especially for venous ulcers), and by off-loading (in the setting of pressure-induced ulcers). Further improvements in the vascularization of the wound bed can also be achieved by applying growth factors (eg, platelet-derived growth factor [PDGF]), by applying bioengineered skin, or even by using occlusive dressings. Indeed, one of the most important effects of occlusive dressings in chronic wounds, in addition to pain relief and absorption of exudate, may be stimulation of granulation tissue formation. Some growth factors, not yet available commercially, have the potential to greatly stimulate angiogenesis. These agents include fibroblast growth factors (FGFs) and vascular endothelial growth factor (VEGF).

Bioengineered skin and autologous or allogeneic skin can stimulate the formation of granulation tissue and, perhaps indirectly, the process of reepithelialization. Particularly noteworthy is the so-called edge effect (migration of the wound's edge toward the wound's center) after the application of bioengineered skin to previously unresponsive chronic wounds. These clinical effects have been observed with bioengineered skin and with simple keratinocyte sheets. It has been hypothesized that these stimulatory effects are due to the synthesis and the release of certain cytokines by the donor cells. However, the situation is probably highly complex, with cross-talk developing between the donor cells and the recipient resident wound cells. This cross-talk leads not only to the release of cytokines but also to the recruitment of other cell types from surrounding tissue and the circulation, to the formation of new blood vessels, and to the laying down of a more ideal extracellular matrix.

The concept of wound bed preparation can help to recognize that chronic wounds have a complex life of their own and that they are not simply an aberration of the normal healing process. This concept allows examination of the different components that need to be addressed in chronic wounds and development of long-term strategies for the more complex issues that lead to failure to heal.

The authors recommend the daily use of the concept of wound bed preparation, which, together with an appropriately chosen wound dressing or tissue substitute, will lead to more effective treatment of acute and chronic difficult-to-treat wounds. Moreover, this area of wound care is also critical to the assessment and evaluation of any new advanced wound healing technologies.

AUTOLOGOUS AND ALLOGENIC SKIN REPLACEMENT

Section 5 of 10

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HYPERLINK "http://www.emedicine.com/derm/fulltopic/topic826.htm" \l "section~TypesofDressings"

Authors and Editors

Introduction

Classification of Wounds

Wound Bed Preparation

Autologous and Allogenic Skin Replacement

Types of Dressings

Acellular Dressings and Skin Substitutes

Engineered Skin Dressings and Substitutes

Perspectives

References

Skin replacement using autologous grafts

The best way to cover large surface wounds is the transplantation of the patient's own skin (ie, split-thickness skin grafts) from an adjacent undamaged area that matches closely in terms of texture, color, and thickness. This surgical procedure inflicts an injury on the donor site analogous to a superficial second-degree burn, allowing spontaneous healing in 2-3 weeks, usually without scarring.

Autograft is the method of choice to achieve definitive coverage of burned skin with good quality of healed skin. This technique has been improved by expanding the surface of the skin graft with a mesh apparatus, depending on the needs of the patient. Recently, as much as 25-30 times expansion has been described. However, excessive meshing usually results in healed skin that is more susceptible to infections and has a basketlike pattern, a major drawback for aesthetic appearance. An alternative is the Meek island graft or sandwich graft. This method allows easier handling of widely expanded autografts than meshed skin. In addition, because the autograft islands are not mutually connected, failure of a few of them does not affect the overall graft take. The Meek technique has been reported to be superior to the mesh procedure for expansion ratios of more than 1:6.

In large surface burns, early closure of burn wounds with autologous skin grafts is limited by the lack of adequate donor sites. A delay of 2-3 weeks is necessary to wait for healing of donor sites before harvesting them again. The split-skin graft from the initial donor site can usually be reharvested 2-3 times and healed autografted wounds. This coverage process is time consuming and, thus, induces high risks of morbidity and mortality, mainly due to bacterial invasion.

Cuono and coworkers3 proposed a 2-step procedure using composite autologous-allogenic skin replacement (de-epidermized skin allografts for dermis substitution and autologous, in vitroreconstructed epidermis for surface covering) in burns. Compton et al4, as well as Hefton and coworkers5, preferred the use of both autologous, in vitroreconstructed and allogenic, in vitroreconstructed epidermal grafts for large-surface wounds.

Although the use of epidermal autografts has markedly advanced the management of extensive burns and saved lives, this technique has major limitations, as follows: (1) at least 3 weeks is needed for growth of cultured epidermal sheets in the laboratory, thus delaying the coverage of wounds; (2) epidermal sheets need to be grafted on a clean wound bed because they are highly sensible to bacterial infection and toxicity of residual antiseptics; (3) the success of the treatment strongly depends on the dexterity of the laboratory and surgical teams, from the production of the sheets to their graft and care after grafting because this material is very fragile; (4) the regeneration of the dermal compartment underneath the epidermis is a lengthy process, and skin remains fragile for at least 3 years and usually blisters; and (5) the aesthetic aspect of the healed skin is less acceptable than the one obtained with a split-thickness graft.

It was recognized early that any successful artificial skin or skinlike material must replace all of the functions of skin and, therefore, consist of a dermal portion and an epidermal portion. It was clinically apparent that a deep burn or other deep and/or large-surface wounds could not be completely closed promptly after injury by using the patient's available autograft donor sites. Moreover, in certain clinical situations (eg, elderly and young individuals), the donor sites themselves (if taken at standard thickness) create new wounds that often take a long time to heal and create additional metabolic stress, infection risk, and scarring.

Wound coverage with allogenic skinOne of the main differences between the cultured epidermal sheet and a split-thickness autograft is the lack of the dermal structure from the cultured autograftable sheets. The absence of dermis is perceived as the major cause for a lower percentage of graft takes and higher fragility and blistering after epidermal sheet transplantation compared to split-thickness autograft. A dermal component protects the basal layer of the epidermis and has a significant impact on the postgrafting biologic responses of the epithelial cells to the differentiation and wound-healing processes.

After early debridement of deep and extensive burns, temporary closure of the wound is usually achieved with cadaver allograft before autografting with cultured epidermal sheets. Instead of completely removing cadaver skin before sheet transplantation, an excision of allogeneic epidermis can be performed with a dermatome to only maintain the allogeneic dermis on the wound. Because nonliving dermis alone may not be rejected, autologous cultured epidermal sheets can be grafted onto it, thus greatly enhancing healing. Indeed, cultured epidermal sheets grafted onto homograft dermis display early rete ridge development and anchoring fibril regeneration, in addition to a graft take of 95%.

Knowing that devitalization of allografts reduces their antigenicity, the use of allogeneic cadaver skin as a biologic dressing is now widely accepted and is usually preferred to synthetic dressings. The preservation of allografts can be performed by different techniques, such as freeze-drying, glutaraldehyde fixation, or glycerolization.

Cryopreservation of homografts with glycerol is the most popular method of cadaver skin processing because freeze-drying is too expensive and glutaraldehyde fixation has proven less efficient. Moreover, skin preservation can reduce the risk of virus transmission from skin grafting, providing time to rid the donor skin of pathogens. Indeed, incubation of cadaver skin for several hours at 37C in glycerol displays a significant virucidal and bactericidal effect. To provide sufficient cadaver skin instantly accessible for the patient with a burn, skin banks, such as the Euro Skin Bank in Beverwijk, The Netherlands, have been well developed through the years. However, allogenic skin banking has a significantly higher cost compared with xenogeneic skin banking and biologic dressings.

TYPES OF DRESSINGS

Section 6 of 10

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HYPERLINK "http://www.emedicine.com/derm/fulltopic/topic826.htm" \l "section~AcellularDressingsandSkinSubstitutes"

Authors and Editors

Introduction

Classification of Wounds

Wound Bed Preparation

Autologous and Allogenic Skin Replacement

Types of Dressings

Acellular Dressings and Skin Substitutes

Engineered Skin Dressings and Substitutes

Perspectives

References

Until the early 1980s, only a few wound care products were available apart from traditional dressings (eg, gauze-based products) and paste (eg, zinc paste) bandages.

The first modern wound dressings introduced during the mid 1980s usually combined 2 main characteristics: moisture keeping and absorbing (eg, polyurethane foams, hydrocolloids) or moisture keeping and antibacterial (eg, iod-containing gels).

During the mid 1990s, the group of surgical dressings expanded into the well-recognized groups of products, such as vapor-permeable adhesive films, hydrogels, hydrocolloids, alginates, and synthetic foam dressings. Additionally, new groups of products, such as antiadhesive, mostly silicone meshes; tissue adhesives; barrier films; and silver- or collagen-containing dressings, were introduced. Finally, in the second half of the 1990s, combination products and engineered skin substitutes were developed. Until the end of 2002, many different dressings had been marketed (see the Table below). Currently, the global tendency demonstrates decreasing numbers of product categories approved both in Europe and in the United States, making the wound dressing market more transparent.

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

Cost effective and covered by health insurance systems

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.