9.1.1 Goals of wound dressing

The skin serves as a barrier (mechanical, chemical, and thermal) that is vital to preventing infection and to maintaining homeostasis (chapter 2.1 to 2.3). Whenever the skin is violated, whether by trauma or by surgery, the protective function, which skin provides, is compromised. Dressings are used to cover wounds until the skin is functionally restored. In many cases, dressings are also used to condition the wound, ie, to prepare it for a definitive procedure designed to restore the integrity of the integument.

Dressings are used for various purposes, depending on the wound environment:

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  moisten or dry a wound

  
  
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  prevent further contamination of a wound

  
  
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  deliver antibiotics to a wound

  
  
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  avoid further trauma to a wound

  
  
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  debride and condition a wound

  
  
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  promote healing.

Most recent literature affirms that for traumatic wounds, a moist wound environment that removes heavy exudates is optimal for wound healing, especially, if migration of fibroblasts to and ingrowth of vessels into the wound is enabled (chapter 4.1). While the formation of an eschar may prevent infection, it will undoubtedly impede reepithelialization. Dressings should ideally limit the moist environment to the wound, and keep the adjacent skin rather dry in order to avoid maceration.

The application of dressings is often relegated to the less experienced members of the treatment team or to outside personnel (with a high turn-over rate) that prevents a regular and good follow-up. Especially complicated or chronic wounds may benefit from specialized personnel known as wound specialists. Otherwise, this may easily result in wounds, which are not adequately monitored. Yet, it is the continuous assessment of wound healing, which is critical to successful outcomes.

There are many types of dressings from the simple to the exotic ( Table 9.1-1 ). The range of dressing materials is everexpanding. While there are many different opinions on which dressings are most appropriate for which wounds, neither in literature nor in practice is there consensus or evidence as to the ideal dressing for a given wound environment. The choice of dressing depends on the surgeon′s assessment of the wound environment and preferences. The following discussion represents what the authors feel is the preponderance of evidence in literature and common practice. Principles will be discussed, rather than attempting to discuss every type of dressing.

9.1.2 Traditional dressings

Traditional dressings include various types of gauze dressings, wet or dry nonadherent dressings, and bulky dressings. They are considered to be low-tech, but they are not necessarily less expensive over the course of treatment than more modern, higher-tech solutions. Such dressings often require more experience than is commonly assumed if they are to be applied correctly. However, they are more generally available than advanced dressings. Gauze dressings come in a variety of sizes and patterns. They are usually made of cotton and have a loose weave, whose size may vary. In the acute setting, gauze dressings are used to absorb drainage from surgical wounds. They are quite effective at wicking away moisture from surgical or traumatic wounds, keeping it away from intact skin. In the setting of an open wound with heavy exudate, gauze dressings are used as a wet-to-dry dressing. In recent years, these dressings have fallen out of favor because of significant pain accompanying the changing of dressing as well as the fact that they are indiscriminate in terms of what adheres to the gauze and is thus debrided. Both exudate and granulation tissue may be eliminated and debrided, respectively. Wet and dry, nonadherent dressings include dressings such as salinemoistened and/or petroleum-based gauzes as well as fenestrated plastic-covered gauze dressings. These may be used in wounds that are clean and have a good granulation bed, in wounds with slight drainage after surgery, or over skin grafts and split-thickness skin graft donor sites. They help lessen the pain of changing dressing, but do not completely prevent adherence of the dressing to dried exudate or blood. This dried material will generally fall off when this type of dressing is changed, resulting in debridement, sometimes causing bleeding and pain. Bulky dressings, often consisting of loose cotton fiber material, may be used to pad casts, to immobilize a joint, or to provide relief from pressure on flap pedicles, or pressure sores on extremities. They are often placed under a splint, which may also be used.

9.1.3 Modern dressings

Modern dressings include some form of hydrogel (jelly-like material with properties ranging from soft and weak to hard and tough), alginate (naturally occurring biopolymer derived from seaweed), or thin covers such as polymer or silicon dressings. They are mostly used for burn patients, chronic wounds such as diabetic ulcers, or the donor site of split-thickness grafts. There does not seem to be a large role for them in the acute trauma setting.

Thin-film, semipermeable dressings are made of polymers, which allow passage of water vapor from the wound and oxygen into the wound, but prevent liquids and bacteria from getting into the wound. These dressings may be used for small surgical wounds and at venous-catheter sites. They are also rather popular to cover donor sites of split-thickness skin grafts, sometimes in combination with alginates to reduce pain.

Silicon dressings have been used to help reduce scar and keloid formation. These dressings are not absorbent and should not be used on moderately or heavily exudating wounds. If used in an acute setting, these dressings are typically applied for surgical wounds with excellent hemostasis. Another major type of modern dressing is negativepressure wound therapy (NPWT). This system is thoroughly discussed in chapter 9.3.

9.1.4 Antimicrobial dressings

Antimicrobial agents may either act as a bactericide or bacteriostatic agent and can be incorporated directly into gauze or hydrogel dressing, or—as a cream—may be applied beneath another type of dressing. These agents are also used to treat open and septic wounds. However, one should take into consideration that these agents may be harmful to tissues and may reduce the activity of the body′s natural defenses. Silver has been used as a broad-spectrum topical agent with antimicrobial properties for decades. The elution properties of several preparations have been studied and proved to be effective for several days to weeks. Silver has good biologic activity against many common pathogens including Escherichia coli, Staphylococcus aureus, streptococci , Pseudomonas aeruginosa, Candida albicans and Enterococcus faecalis as well as antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus (VRE) [1]. Interestingly, Acinetobacter baumanii seems to be naturally resistant to topical silver dressings [2]. Susceptible bacteria do not seem to develop resistance to silver due to its activity at multiple bacterial target sites, making it suitable for long-term use [3]. However, it is less effective against bacteria in the biofilm state. There is evidence that the adjunctive use of silver with systemic antibiotics is additive and, in some cases, even synergistic. However, there is evidence that silver is toxic to fibroblasts and keratinocytes both in in vitro and in animal studies [4]. Furthermore, it could inhibit cellular proliferation and leukocyte activity. In mammalian cells, however, silver has only been associated with minimal toxicity at low concentrations [5]. There are few studies that examine the systemic absorption of silver from silver-impregnated dressings. Silver nanoparticles also affect the DNA of fibroblasts and stem cells in mouse cell lines [6].

There are many types of dressings and topical creams containing silver. The method of delivery and the quantity of free silver released into tissues is different in each. Silver sulfadiazine has been used extensively in burn patients, but does not offer sufficient activity against gram-negative organisms. Accordingly, cerium nitrate has been added to silver sulfadiazine to augment its effectiveness in burn patients. One drawback of prolonged local use of silver-containing agents may be the permanent deposition of silver molecules within the dermal layers of the skin, resulting in tattoo-like discoloration. More recently, silver has been applied in nanocrystalline form to an effective absorbent dressing, which can be used to treat wounds being prepared for staged coverage (eg, silver-containing alginate). These dressings must be removed before an MRI is performed and should not be used in combination with petroleum dressings. They may be left in place for 3–7 days, depending on the product ( Fig 9.1-1a–d ).

Povidone-iodine-impregnated dressings were commonly used in the past for military wounds and burns. The substance exhibits excellent activity against most bacterial, fungal, and viral pathogens. There are varying reports concerning the tissue toxicity and effect on wound healing of povidone-iodine preparations [7], although more recent methods of application may have ameliorated this concern. Povidone-iodine has been shown to be toxic to synovium and cartilage and should, therefore, be handled with care or even avoided in the setting of complex bone or articular injuries [8]. In the acute setting, most surgeons now consider it to be useful for cleansing a surgical site, but not for packing traumatic wounds, because of the presumed tissue toxicity and the availability of alternative, less-toxic solutions.

Dakin′s solution (sodium hypochlorite), a chlorine-releasing solution originally consisted of concentrations of 0.4–0.5% sodium hypochlorite and boric acid (4%). However, in recent years, it has been diluted to half-strength (0.25%), quarter-strength (0.125%), and down to 0.0125% solutions in order to reduce the tissue toxicity of the original solution. It exhibits relatively broad antibacterial activity, including MRSA, VRE, and Pseudomonas species. It has been shown in vitro that diluted solutions (0.0125%) continue to show antibiotic properties, without any detrimental effect on keratinocytes. Dakin′s solution is inherently unstable and so must be made up as needed.

Mafenide acetate and mafenide hydrochloride are antibacterial agents, though the hydrochloride solution is more potent. They both exhibit wide antimicrobial activity and are uniquely effective against Acinetobacter baumanii. Their usefulness in burn patients has been well established [9]. As mafenide acetate has been shown to inhibit DNA and protein synthesis in wounds and to delay reepithelialization, prolonged use in open wounds is not indicated. However, as an initial treatment of open wounds, it appears to be useful.

Finally, hydrogen peroxide has successfully been used as an antiseptic and antibacterial agent for a long time due to its oxidizing effect. While its use has decreased in recent years with the popularity of readily available over-the-counter products, it is still used by many hospitals and doctors.

9.1.5 Hemostatic dressings

The major cause of early mortality in trauma victims, military or civilian, is uncontrolled hemorrhage. Dressings have been developed, largely for military use, which can be applied directly to hemorrhagic wounds in order to immediately stop bleeding. These dressings are typically made of chitosan, zeolite or derivatives of marine algae.

A number of dressings are currently based on chitosan, a derivative of chitin. Chitin forms the exoskeleton of crustaceans. Chitosan is produced by the deacetylation of chitin. It is provided in granules or on a sponge. It acts by binding to receptors on red blood cells, forming a gel. It works regardless of hypothermia, the presence of anticoagulants, or depletion of coagulation factors. Unlike zeolite dressings, it does not produce an exothermic reaction. Zeolite is an aluminosilicate substance similar to that found in volcanoes. It acts by rapidly absorbing water from blood, thus concentrating coagulation factors and potentiating the coagulation cascade. It may be applied as a powder or on a sponge. It must be applied directly to the source of bleeding and, therefore, may be difficult to apply directly to deep arteries. The major drawback is that it creates an exothermic reaction, which can cause burns. It has recently been combined with silver to form an antimicrobial dressing and has been successfully applied for the treatment of combat wounds.

Poly-n-acetylglucosamine is derived from marine algae. It appears to work by sealing the wound and facilitating the coagulation cascade. The procoagulative effect abates within a few hours, but by then, the patient can hopefully receive definitive care. This dressing is currently in use by the US military. Dressings that are saturated with fibrin, thrombin, or calcium have also been used, but appear to be less effective, with considerably more bleeding seen in clinical practice than with those mentioned before.

9.1.6 Biological dressings

Biological dressings are being used more and more in acute trauma. While generally considered temporary dressings, they work in concert with the natural healing process until the wound is prepared to accept definitive coverage, such as a split-thickness skin graft. They may be composed of allograft skin, xenograft skin, or collagen matrices (chapter 10.2). The goal of these dressings is to conserve water, protein and electrolytes, and reduce infection. By providing a substrate that allows ingrowth of fibroblasts and promotes angiogenesis, these dressings prepare the wound to accept skin grafts.

For many years, xenografts, particularly porcine grafts, have been used for burn patients to temporarily cover wounds and allow time for skin to be reharvested or for the patient to stabilize before split-thickness skin grafting. To prevent rejection by the host, these grafts are processed to remove most antigens. Nevertheless, in time, they will be rejected, necessitating replacement by native skin. Similarly, allograft skin can be used.

Bilayer collagen matrix dressings ( Fig 9.1-2a–d ) are composed of bovine type I collagen, which has been processed to provide cross-linked collagen fibers. These degrade slowly and are replaced by neodermis [10]. This layer of collagen is covered by a thin silicone layer, which helps to prevent the colonization of the collagen matrix by bacteria and the loss of water. It is transparent, so the wound can still be visualized. These dressings may be combined with negative-pressure wound therapy to foster angiogenesis and decrease the period before split-thickness skin grafting from 2–3 weeks to 7–10 days. Once the collagen matrix is ready to accept a skin graft, it will change to a salmon color. Nowadays, single-layer matrices are available that allow a one-stage surgical procedure, ie, simultaneous application of both matrix and skin grafts. With each of these dressings, it is important that the wound bed be rendered as sterile as possible. Bacterial colonization will significantly decrease the survival rate of such grafts.

9.2.1 Nonresorbable antibiotic bead therapy

Local antibiotic therapy is frequently used to prepare contaminated dead space for eventual bone grafting or substitution with vascularized bone or muscle and coverage. Antibiotic beads are frequently made by mixing polymethyl methacrylate (PMMA) with an appropriate antibiotic. The beads are packed into the open or dead space and then the wound is either closed or covered with a semipermeable membrane, which is the so-called bead-pouch technique ( Fig 9.2-1a–d ). The majority of the drug is eluted over the first 24 hours. However, some studies suggest elution may occur in small doses for as long as 90 days [11, 12]. Antibiotic elution is related to the surface area of the antibiotic spacer used. Therefore, small beads arrayed in chains will elute more than larger beads, which will elute more than a block spacer. There are many considerations that may guide the choice of the shape and the size of the antibiotic beads, but if elution of antibiotics is the primary aim and all other factors are the same, the use of small beads is advised.

There are a number of ways in which local antibiotics can be used. Antibiotic-coated implants such as intramedullary nails are currently available in some locations in Europe, but are not available in the United States at this time. Antibiotic beads are often applied using the bead-pouch technique to provide large concentrations of antibiotic in an area of bone deficit that has been severely contaminated. Finally, some surgeons now prefer to use a block of cement covered with antibiotics in order to provide a high concentration of antibiotic and also to allow the formation of a biologically active membrane around the cement block. Furthermore, the block of cement acts as a spacer and eases subsequent reconstruction of the bone and/or soft tissues, eg, nonvascularized or vascularized bone and/or fasciocutaneous flap, muscle or musculocutaneous flap.

A wide variety of antibiotics have been used in beads, ranging from aminoglycosides to vancomycin to a third-generation fluoroquinolone[11–13]. The requirements of an antibiotic to be used in beads include:

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  water solubility

  
  
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  broad spectrum

  
  
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  good tolerance

  
  
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  heat stability

  
  
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  bactericidal in low concentrations

  
  
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  availability in powdered form [11].

The most commonly used antibiotics are tobramycin and vancomycin. We frequently combine 2.4 g of powdered tobramycin or 2.0 g of vancomycin with a 40 g pouch of Palacos^® Bone Cement (Biomet Orthopedics, Inc., Warsaw, IN, USA). It is important to select a type of cement that keeps a dough-like consistency for a number of minutes in order to allow the formation of the beads. If the wound contains multiple organisms or a broad spectrum of coverage is required, both 2.4 g of tobramycin and 1.0 g of vancomycin can be combined with a single packet of polymethyl methacrylate cement. Beads can be created either using commercially available molds or by hand rolling the beads. Regardless of which technique is used to create the beads, they should be strung on a strong nonresorbable suture. Commercial formulations of antibiotic beads are available outside the United States, but are not currently available within the United States. Precise mixing directions and uniformity of size cannot be achieved with hand rolled beads, leading to differences in drug elution from the varying surface areas of the beads [14]. It should be noted that rarely systemic levels of antibiotics have been detected in patients. Therefore, this technique should be used with caution in patients with antibiotic allergies or severe renal disease.

There is a large body of evidence from animal studies documenting successful use of antibiotic beads for both the treatment of contaminated wounds and chronic osteomyelitis [12, 14]. However, the clinical data is limited due to studies that are primarily retrospective and/or have a small sample size. There are no well-designed prospective randomized clinical trials to document the efficacy of polymethyl methacrylate beads. Despite this shortcoming, the combination of solid animal data and suggestive clinical data has led to the widespread use of antibiotic beads and the bead-pouch technique [11, 12, 14–16].