Practical design session 02: Fistula project

Once a diagnosis of wound infection has been confirmed and antibiotic sensitivities identified, appropriate management regimens should be considered, with a high priority given to reducing the risk of cross infection. It is important to treat the patient as a whole and not the infection alone, so management strategies must be based on data derived from an holistic assessment of the needs of the individual.⁷⁴ The main treatment objective will be to reduce rather than eradicate the bacterial burden within the wound margins. In addition to antibiotic therapy, there are two main generic groups of wound management products that have the potential to reduce the bacterial burden in the wound. These are compounds containing silver or iodine.⁷⁵

6.1 Antibiotic therapy

Antibiotics are chemical substances produced by a micro-organism that have the capacity, in dilute solutions, to selectively inhibit the growth of or to kill other micro-organisms.⁶² Whereas it is now generally accepted that systemic antibiotics are essential for the management of clinically infected wounds, the choice of

antibiotic to be used is not always apparent. Only after a comprehensive assessment process including consideration of patient characteristics, the results of microbiological investigations and the identification of both the nature and location of the wound, can the most appropriate antibiotic be identified.

Some patients benefit from antibiotic prophylaxis whereas others may not. An increased risk of SSI occurs with an increasing degree of wound contamination regardless of other risk factors⁵⁷ and as the number of risk factors increases for a given type of operation. The best time for antibiotic prophylaxis is within one hour before the time of incision.⁷⁶ Antibiotic prophylaxis is indicated clearly for most clean-contaminated and contaminated operations. Parenteral antibiotic is commonly used but oral antibiotics can be administered for prophylaxis provided the agent is chosen carefully based on spectrum, bioavailability and the potential need for the patient to take nothing orally for several hours before general anaesthesia. Topical 2% muciprocin ointment applied to the nares of patients who are chronic carries of Staphylococcus aureus reduces the incidence of wound infection.⁷⁷ Antibiotics for dirty operations represent treatment for an infection, not prophylaxis.

Antimicrobial therapy can be administered intravenously or orally depending on the clinical severity of infection. Although eventually tailored to the specific organisms found on culture studies, empiric therapy can be initiated by considering the most likely organisms to be encountered based on the class of operation performed and

the likelihood of resistant organisms. Broad coverage is encouraged initially, and regimens typically include second generation Cephalosporins plus Metronidazole. B-lactamase inhibitor combinations, and Carbapenems. Vancomycin should be used in the face of suspected or known resistant organisms particularly with the rise of epidemic strains of Methicillin-Resistant Staphylococcus Aureus (MRSA). The overuse of broad-spectrum antibiotics will only serve to exacerbate the situation.

It could therefore be argued that all antibiotic use should be based on known sensitivities.

6.2 Iodine

Iodine is an element that has antiseptic properties. It is active against a number of pathogens. In the past its use has been limited by the fact that elemental iodine can be absorbed systemically, is almost insoluble and can be an irritant to the skin.

In wound management iodine is used in two forms: (a) Cadexomer iodine - a polysaccharide starch lattice containing 0.9% elemental iodine that is released on exposure to wound exudate. (b) PVP-1 (Povidone iodine) - an iodophor composed of elemental iodine and a synthetic polymer. Both have different physical characteristics that relate to the component parts and the iodine concentration of available iodine that is released when in use. Clinically iodine is indicated for wound cleansing, wound bed preparation (the stimulation and influence of specific cells

involved with the immune system) and the prevention and management of wound infection⁷⁸.

6.3 Silver

Recently a number of dressings containing silver have become available, although silver and silver compounds have been routinely used in clinical practice as bactericidals for over a century. Silver interferes with the bacterial electron transport system and inhibits the multiplication of the bacteria. However, to achieve this, silver ions have to be able to enter a cell. The chemical bonding of silver with a sulphonamide antimicrobial - sulphadiazine - has resulted in the development of a safe broad-spectrum agent for topical use (e.g. Flamazine). In this formulation silver is released slowly from the transport medium in concentrations that are selectively toxic to microorganisms such as bacteria and fungi. This type of silver product has been used successfully in the management of acute and chronic wounds⁶². Products that can sustain the interaction of silver with micro-organisms in the exuding wound are likely to be more effective in preventing/controlling local infection as potentially more silver ions will be available to enter bacterial cells. This assumes that the concentration of silver in the solution is both correct and maintained.

6.4 Incision and drainage

Incision and drainage is commonly used in the treatment of abscesses. The operative site is incised sharply and the underlying purulent fluid is removed. All inflamed tissue loculations encountered are broken, either bluntly or sharply under local anaesthesia and intravenous (IV) sedation or general anaesthesia (depending on the clinical severity of infection). Any obvious nonviable tissue is debrided to healthy-appearing or bleeding tissue. The wound created is thoroughly irrigated with saline and packed.

6.5. Wet to dry dressings

After open drainage of an incisional SSI, attention is focused on healing of the subcutaneous and cutaneous elements of the wound thus created. Immediate wound closure is not an option because of the high risk of infection recurrence. The objective of wet to dry dressing is to allow the wound to close over a period of time from its base to the surface. This can be effectively achieved by packing the wound with wet dressings and removing these dressings after they have been allowed to air-dry. The dressing changes should occur at least three times daily depending on the growth activity of the wound and the degree of wound exudate formation and bacterial colonization. Dressing the wound instead of leaving it open allows for more rapid wound healing,^80-82 and removal of the dressing debrides necrotic tissue and wound fibrinous exudate. The wound dressing also provides a moist environment for

granulation tissue in-growth and may act as a protective barrier against the environment.

6.6 Delayed primary closure

With appropriate prophylactic antibiotic use, certain clean-contaminated (severe acute cholecystitis) or contaminated (localized, perforated appendicitis) operations may have their wounds initially left open with treatment for the first 5 days consisting of wet to dry dressing changes. In the absence of active skin or soft tissue infection signs, consideration may be given to delayed primary closure.

Wound edge approximation may help to expedite closure of the wound. The objective, however, is still to allow healing from the base and to avoid a deep fluid collection and subsequent abscess formation.

6.7 Growth factors

Agents such as epidermal and fibroblast growth factors coordinate the various processes of wound healing by regulating cell proliferation, migration, and secretion.

Preliminary clinical work seems to indicate that the eventual use of topical growth factors will be in the treatment of chronic ulcers, which are very difficult and expensive to treat. The higher cost would likely not allow their use in routine acute and infected wounds, which usually heal well anyway. However, there may be a role

for their use in the prevention of excessive fibroplasia and scarring that may accompany certain acute wounds.

6.8 Liposomal antibiotic

Several antibiotics are being prepared in a liposomal formulation, which allows an effective concentration of selected drugs to remain at active levels for longer periods of time. The drug in its primary form is prepared in a liposomal vesicular matrix. This preparation increases the duration of bioactivity.