Annals of the MBC - vol 3 - n' 1 - March 1990


El Morsi H.A.R.

Plastic & Reconstructive Surgery Department, Maadi Armed Forces Hospital, Al-Khobar, Saudi Arabia

SUMMARY. The various risk factors involved in burn wound infection are reviewed, with reference to the patient's condition and to particular microbes. A number of factors, both systemic and local, can confound the diagnosis of infection and these are listed. A description is given of methods for assessing the microbial status of burn wounds. Fungal infection and immunological incompetence are also considered.

Risk factors in burn wound infection

Patient Factors:

  1. Extent of burn > 30 per cent of body surface
  2. Depth of burn. full-thickness & partial thickness
  3. Age of patient
  4. Pre-existing disease
  5. Wound dryness
  6. Wound temperature
  7. Secondary impairment of blood flow
  8. Acidosis

Microbial Factors:

  1. Density >
  2. Motility
  3. Metabolic products
  4. Endotoxins
  5. Exotoxins
  6. Permeability factors
  7. Other factors
  8. Antimicrobial resistance 105 organisms ner cram of tissue

Burn wound infections are least common in young adults and occur with greater frequency in the paediatric age group. Infection in general occurs more frequently in the elderly burn patients, that is those above 60 years, than in young adults. Pre-existing immunological deficiencies and metabolic abnormalities, the most common ones being obesity and malnutrition, are predisposing factor5.
The importance of the local blood supply is indicated by the relative resistance to infection of a partial-thickness burn compared to a full-thickness burn.
A hyperdynamic general circulation appears to be essential to provide the increased wound blood flow which delivers the nutrients and substrates necessary for uncomplicated wound healing.
Subsequent clinical application of such wound care established the effectiveness of topical chemotherapy in reducing the incidence of burn wound sepsis and its associated mortality.
The exposure technique advocated by A.B. Wallace should be supplemented by topical chemotherapy. The use of mafenide acetate burn cream, applied twice a day with the sterilely gloved hand, limits bacterial proliferation in the burn wound and has significantly reduced the occurrence of invasive burn wound infection.
Mafenide acetate cream, silver sulphadiazine cream, and 0.5% silver nitrate soaks have been used in a sufficiently controlled manner.
Frequent examination of the burn wound is therefore essential as also monitoring of the function of other organ systems in order to diagnose infection at a time when the course of a septic complication can be favourably altered.
Hypotension and respiratory distress often accompany severe sepsis but may also be due to blood loss and aspiration respectively.

Factors confounding the diagnosis of infection in burn patients

Systemic factors:

1 - Hypermetabolism

  1. Hyperthermia
  2. Tachycardia
  3. Hyperventilation
  1. Accentuated by:
  1. Inhalation injury
  2. Mafenide acetate topical therapy
  3. Excess dietary carbohydrate
  1. Attenuated by:
  1. Narcotics
  2. C.N.S. injury

II - Central nervous system dysfunction

  1. Cerebral oedema
  2. Narcotic effects
  3. Sensory deprivation

III - lmmunosuppression

  1. Post-injury neutrophil changes
  2. Hormonal response to injury
  3. Secondary effects of therapy e.g. silver sulphadiazine wound infection, but occurs later in the course of the disease.

Local factors: Advantages

I - Altered tissue consistency
A. Eschar formation
B. Fat liquefaction

organisms Identifies bacteria, yeasts,

fungi and viruses

II - Colour changes in eschar
A. Maturation of wounds sections
B. Haemorrhage due to minor trauma Limitations

III - Peripheral nerve injury falsely positive
A. Burn injury

1. Heat
2. High voltage electricity

B. Pressure injury

1. Position
2. Splints

Does not sample Does not sample Errors in histological eschar space subeschar space interpretation

IV - Oedema

A. Wound
B. Pulmonary

1. Fluid overload
2. Myocardial insufficiency

Leakopenia, a frequent accompaniment of severe gram-negative sepsis, may be a complication of therapy, as has been reported for silver sulphadiazine.
The difficulty,In evaluating the systemic signs of infection in the burn patient necessitates frequent careful evaluation of the burn wound per se and any other organ or tissue suspected of harbouring infection.
The occurrence of local, multifocal or generalized dark brown, black or violaceous discoloration of the burn wound is one of the earliest and most frequently observed signs of bum wound infection.
Conversion of a partial-thickness injury to full-thickness necrosis is a more reliable sign of bum The most useful surface culture technique has in our experience been the contact plate which provides quantitative information and, when selective media are used, can provide specific qualitative information as well.
Wound biopsy is a much more accurate and reliable means of assessing the microbial status of the burn. The biopsy is performed as a ward procedure and the sample is obtained from that area of the wound considered, on the basis of clinical signs, to be a site of infection.
Gram's stain or haematoxylin and eosin stain are most useful for the identification of bacteria in tissue while periodic acid-Schiff stain or silver methenamme stain are best for fungal identification.
Other histological signs characteristic of bum wound infection include: dense microbial growth at the non-viable/viable tissue interface, haemorrhage present in unburned subcutaneous tissue, and exaggeration of the normally mild inflammatory response present in viable tissue immediately adjacent to the burn.
A diagnosis of invasive wound infection demands not only a change in wound care, but also the institution of other therapeutic measures.
In the immediate post-burn period, group a haemolytic streptococcal cellulitis occurs infrequently and characteristically responds promptly to the administration of penicillin.
General measures to support organ function, i.e. fluid, red cell and pharmacological agent administration, ventilatory support, and administration of nutrients, should be employed as necessary.
The survival of patients who develop extensive burn wound infection is relatively uncommon.

Fungal infection

The recovery of non-bacterial organisms from the burn wound has increased with the use of topical antibacterial agents. Candida species are the most frequent non-bacterial organisms present in the burn wound.
Biopsy is required for confirmation of fungal infections that occur in severely injured or critically ill patients, especially those with impaired host defence who have received antibiotics. Diagnosis of invasive infection due to the Phycomyeetes necessitates therapeutic measures as indicated by both local changes and the patient's systemic response to infection. All infected and necrotic tissue should be removed surgically, rapid extension along fascial planes is characteristic, and the extent of excision required is large. Progressive extension of a phycomycotic infection or evidence of systemic spread are indications for institution of systemic antiftingal therapy.
Aspergillus and Fusarium, the true fungi most often recovered from burn wounds, are also typically localized, seldom spread across fascial planes, and in most cases can be adequately dealt with by local excision.
The treatment of fungal burn wound infection is guided by the location and depth of infection. Infections limited to the subcutaneous tissue are treated by wide local excision with the wound packed open to permit subsequent daily examination.
Evidence of systemic fungal infection or progressive local extension of such infections warrant systemic antiftingal treatment using both amphotericin B and 5-fluorocytosine.

Immunological incompetence

The persistence of infection as the most common cause of morbidity and mortality in burn patients reflects the far-ranging immunocompetence in such patients.
Early treatment of wound and other infections and the use of immunological enhancing agents, as they are developed, will further improve the survival of extensively burned patients.

RËSUMÉ. L'Auteur passe en revue les divers facteurs de risque dans les infections à la suite des brûlures, par rapport aux conditions du patient et aux microbes particuliers. Beaucoup de facteurs, soit systémiques soit locaux, peuvent rendre difficile le diagnostic et ces facteurs sont indiqués. On décrit des méthodes pour évaluer l'état microbien des plaies, Enfin on considère l'infection fongique et l'insuffisance immunologique.


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