Treatment of Infected Burns

Amanda van den Broek

Infection is the most common and most serious complication of a major burn injury related to burn size. Sepsis accounts for 50-60% of deaths in burn patients today despite improvements in antimicrobial therapies. Infection is promoted by loss of the epithelial barrier, by malnutrition induced by the hypermetabolic response to burn injury, and by a generalized post-burn immunosuppressant due to release of immuno reactive agents from the burn wound. Burn injury leads to suppression of nearly all aspects of immune response. Post-burn serum levels of immuno globulins, fibronectin, and complement levels are reduced, as well as a diminished ability for opsonization. Chemotaxis, phagocytosis, and killing function of neutrophils, monocytes, and macrophages are impaired. If bacterial counts are 105, wound infection should be suspected and treated with antibiotics.

Therapeutic Antibiotics - Depending on the infection, therapy may continue for several days. Systemic antibiotic treatment for burn wound sepsis is continued for at least 72 hours after evidence of sepsis has resolved. If the wounds appear clean, other sources such as the lungs, the kidney, and peripheral veins should be suspected. In the absence of a confirmed organism or site, antibiotic selection should be based on routine surveillance cultures. Empiric antibiotic choice should also be based on sensitivities of the burn facility's endogenous organisms. Commonly Vancomycin, Imipenem, Timentin or Ceftazidime for coverage against the usual strains of Staph. aureus and Pseudomonas aeruginosa are used. Routine perioperative antibiotics should also take ward-endogenous organisms into account. Post-operative antibiotics are continued until quantitative excisional wound biopsies from surgery are identified.

Currently, a number of topical agents are available to assist in microbial control of the burn wound, including silver sulfadiazine, mefenide acetate, 0.5% silver nitrate, bacitracin/polymyxin B, mupirocin, and Mycostatin. No single agent is totally effective and each has advantages and disadvantages. Almost all agents will affect wound healing and increase metabolic rate.

• Silver sulfadiazine (e.g. Silvadene or SSD) is the most commonly used topical antimicrobial agent in burns. It has a broad spectrum of antimicrobial coverage including gram positive bacteria, most gram negative bacteria, and some yeast forms. Unlike mafenide or silver nitrate, silver sulfadiazine does not hinder epithelialization, although it does hamper contraction of fibroblasts. It is painless on application, has high patient acceptance, and is easy to use with or without dressing.
• Mafenide acetate is one of the oldest effective topical antimicrobial agents. Mafenide has a broad spectrum of antimicrobial activity, including silver sulfadiazine-resistant Pseudomonas and enterococci, but reduced antifungal properties. Mafenide cream is toxic to epithelial cells and fibroblasts. Unlike other topical agents, mafenide has good penetration through the eschar. For this reason mafenide is commonly used on dirty or infected burn wounds, or electrical burns, and on burned ears to prevent chondritis. Mafenide can cause an allergic skin rash. Through carbonic anhydrase inhibition, mafenide can also cause bicarbonate wasting in the kidneys, hyperchloremia, systemic metabolic acidosis and compensatory hyperventilation.
  
• Silver nitrate 0.5% solution is a broad spectrum, non-penetrating, painless antimicrobial agent. It requires multiple daily applications on burn dressings and is messy and staining. The solution is hypotonic; so electrolyte leeching, hyponatremia, and hypokalemia are common side-effects.
  
• Petroleum-based antimicrobial ointments such as bacitracin and/or polymyxin B are clear on application, painless, and allow for easy wound observation. These agents are commonly used for treatment of facial burns, graft sites, healing donor sites, and small partial-thickness burns.
  
• Mupirocin (e.g. Bactroban) has improved activity against gram positive bacteria, especially methillin resistant Staph. aureus (MRSA) and selected enteric bacteria.
  
• In severely burned patients (>40% BSA), the combination of Mycostatin ointment or powder with other topical agents reduces the incidence of fungal superinfection and improves antimicrobial action. Mycostatin should not be combined with mafenide, however, because both become inactivated. In addition, Mycostatin 5-15 ml given orally 3 times daily reduces alimentary fungal overgrowth. This regimen has markedly decreased the incidence of candida septicemia.

Source: http://www.totalburncare.com/orientation_postburn_infection.htm