Annals of the MBC - vol 3 - n' 1 - March 1990
THE DIAGNOSIS AND TREATIVIENT'OF INFECTION IN THE BURN
PATIENT
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:
- Extent of burn > 30 per cent of body surface
- Depth of burn. full-thickness & partial thickness
- Age of patient
- Pre-existing disease
- Wound dryness
- Wound temperature
- Secondary impairment of blood flow
- Acidosis
Microbial Factors:
- Density >
- Motility
- Metabolic products
- Endotoxins
- Exotoxins
- Permeability factors
- Other factors
- 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
- Hyperthermia
- Tachycardia
- Hyperventilation
- Accentuated by:
- Inhalation injury
- Mafenide acetate topical therapy
- Excess dietary carbohydrate
- Attenuated by:
- Narcotics
- C.N.S. injury
II - Central nervous system dysfunction
- Cerebral oedema
- Narcotic effects
- Sensory deprivation
III - lmmunosuppression
- Post-injury neutrophil changes
- Hormonal response to injury
- 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.
BIBLIOGRAPHY
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1971.
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sulfadiazine silver. JAMA, 241: 1928, 1979.
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