- Mar 30, 2007
Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.
Burn wound infections
[FONT="]Although burn wound surfaces are sterile immediately following thermal injury, these wounds eventually become colonized with microorganisms. The nature and extent of the thermal injury along with the types and amounts of microorganisms colonizing the burn wound appear to influence the future risk of an invasive wound infection. Gram-positive bacteria that survive the thermal insult, such as staphylococci located deep within sweat glands and hair follicles, heavily colonize the wound surface within the first 48 h unless topical antimicrobial agents are used. Eventually (after an average of 5 to 7 days), these wounds are subsequently colonized with other microbes, including gram-positive bacteria, gram-negative bacteria, and yeasts derived from the host's normal gastrointestinal and upper respiratory flora and/or from the hospital environment or that are transferred via a health care worker's hands. Over the last several decades, gram-negative organisms have emerged as the most common etiologic agents of invasive infection by virtue of their large repertoire of virulence factors and antimicrobial resistance traits. If the patient's host defenses and therapeutic measures (including excision of necrotic tissue and wound closure) are inadequate or delayed, microbial invasion of viable tissue occurs, which is the hallmark of an invasive burn wound infection. [/FONT]
Topical Antimicrobial Therapy
Widespread application of an effective topical antimicrobial agent substantially reduces the microbial load on the open burn wound surface and reduces the risk of infection. By controlling infection, effective topical antimicrobial therapy decreases the conversion of partial-thickness to full-thickness wounds, but its use is adjunctive to early excision therapy. Selection of topical antimicrobial therapy should be based on the agent's ability to inhibit the microorganisms recovered from burn wound surveillance cultures and monitoring of the nosocomial infections acquired in the burn unit. Prescription is also based on the individual preparation of the topical agent (e.g., ointment or cream versus solution or dressing) and its pharmacokinetic properties. Burn units may rotate the use of various topical antimicrobial preparations on a regular basis to decrease the potential for development of antibiotic resistance. Topical antibiotic agents should first be applied directly to the patient's dressings before application to the burn wound to prevent contamination of the agent's container by burn wound flora.
The most widely used topical antimicrobial agents and new silver nanocrystalline dressings that are based on the bactericidal properties of the silver ion. The inhibitory action of silver is due to its strong interaction with thiol groups present in the respiratory enzymes in the bacterial cell. Silver has also been shown to interact with structural proteins and preferentially bind with DNA nucleic acid bases to inhibit replication . For this reason, silver has recently been shown to be highly toxic to keratinocytes and fibroblasts and may delay burn wound healing if applied indiscriminately to debrided healing tissue areas . Moist exposure therapy using a moisture-retentive ointment (MEBO-Julphar; Gulf Pharmaceutical Industries, United Arab Emirates) has recently been shown to act as an effective antibacterial agent while promoting rapid autolysis debridement and optimal moist wound healing in partial-thickness injury . Moisture-retentive ointment also resulted in earlier recovery of keratinocytes with improved wound healing and decreased scar formation . The topical antimicrobial agents reviewed are primarily used in burn center patients with full-thickness or deep partial-thickness burn wounds.
Silver nitrate. Silver nitrate is rarely used nowadays in modern burn units because the deposition of silver discolors the wound bed and other topical agents are available that are easier to use and have less potential toxicity. Silver nitrate is most effective before the burn wound becomes colonized. The burn wound needs to be cleansed of emollients and other debris before a multilayered dressing is applied to the burn wound and subsequently saturated with silver nitrate solution. Effective use of this preparation therefore requires continuous application with secondary occlusive dressings, making examination of the wound difficult. The silver ion in AgNO3 also quickly binds to elemental chlorine ions, so that repeated or large-surface application of this solution may lead to electrolyte imbalance. Silver nitrate antibacterial activity is limited to the burn wound surface. This agent demonstrates bacteriostatic activity against gram-negative aerobic bacteria such as Pseudomonas aeruginosa and Escherichia coli, but it is not active against other genera, including Klebsiella, Providencia, and Enterobacter. Silver nitrate also has limited antifungal activity, so that nystatin should be used concomitantly. Silver sulfadiazine. Silver sulfadiazine is the most commonly used topical antibiotic agent for both ambulatory and hospitalized burn patients. This agent is a combination of sodium sulfadiazine and silver nitrate. The silver ion binds to the microorganism's nucleic acid, releasing the sulfadiazine, which then interferes with the metabolism of the microbe. Although silver sulfadiazine dissociates more slowly than silver nitrate, there is still poor penetration into the wound. Silver sulfadiazine is only absorbed within the surface epidermal layer, which limits its effectiveness in some patients with severe injuries.
Mafenide acetate. Topical mafenide acetate cream allows open burn wound therapy and regular examination of the burn wound surface because it is used without dressings. The burn wound surface is cleansed of debris prior to application of the cream, and the treated burn wound surface is left exposed after the cream is applied for maximal antimicrobial effect. Mafenide acetate is applied a minimum of twice daily and has been shown to penetrate the burn eschar.
Mafenide acetate (Sulfamylon) cream has a broad spectrum of activity against gram-negative bacteria, particularly Pseudomonas aeruginosa, but has little activity against gram-positive aerobic bacteria such as Staphylococcus aureus. This agent also inhibits anaerobes such as Clostridium spp. Because protracted use of mafenide acetate favors the overgrowth of Candida albicans and other fungi, this agent should be used in combination with nystatin to prevent this complication due to its limited antifungal activity.
Despite its antibacterial potency, mafenide acetate is not as widely used as other agents because of its toxicity profile. This compound is converted to p-sulfamylvanzoic acid by monoamide oxidase, a carbonic anhydrase inhibitor, causing metabolic acidosis in the burn patient
Acticoat A.B. dressing/Silverlon. This product is a specialized dressing that consists of two sheets of high-density polyethylene mesh coated with nanocrystalline silver (e.g., ionic silver with a rayon-polyester core). The more controlled and prolonged release of nanocrystalline silver to the burn wound area allows less-frequent dressing changes, reducing the risk of tissue damage, nosocomial infection, patient discomfort, and the overall cost of topical therapy (
Mupirocin (Bactroban). Mupirocin (pseudomonic acid A) is a fermentation product of Pseudomonas fluorescens. This antibiotic has potent inhibitory activity against gram-positive skin flora such as coagulase-negative staphylococci and Staphylococcus aureus, including
Nystatin. Nystatin (Mycostatin or Nilstat) is produced by Streptomyces noursei and has potent antifungal effect by binding to the sterols in the fungal cell membrane. However, since nystatin has no activity against bacteria, it should be used in combination with a topical agent that has activity against the broad spectrum of pathogenic bacteria that cause burn wound colonization and infection.
Other topical antimicrobials. Several other topical antimicrobials have also been used for topical burn therapy, including gentamicin sulfate (0.1% water-soluble cream), betadine (10% povidone-iodine ointment), bacitracin-polymyxin ointment, and nitrofurantoin.
Prophylactic Systemic Antibiotics: Administration of systemic antibiotic therapy may also cause antibiotic-associated diarrhea due to the overgrowth of toxigenic strains of Clostridium difficile.
Exposure to prophylactic antibiotic therapy may also increase the resistance of endogenous and pathogenic bacteria to a wide variety of antibiotics, making the subsequent treatment of clinically overt infections in the burn patient more