surgical prophylaxis

Principles

Pathogenesis

· 1st step in infection is bacterial contamination

· if appropriate antimicrobial agent present in adequate concentrations, wound infection less likely

· allows

· prevention of bacterial invasion and proliferation

· protection until local defence mechanisms capable of eradicating bacteria

· antibiotic must be in tissues in early period to be effective

· administration of antibiotics after contamination does not reduce infection rates

· preoperative antibiotic administration provides adequate tissue antibiotic concentrations at the time of contamination

· additional intraoperative administration required for prolonged procedures

· postoperative administration justified to maintain tissue antibiotic levels

· likely that no more than one or two additional doses required

· disadvantages of prolonged administration

· antibiotic-related side-effects

· superinfections

· masking signs of unrelated infections

· development of resistant strains of pathogenic organisms

Infective agents

· varies widely among institutions

· most common G+ bacteria (50%)

· S. aureus

· S. epidermidis

· other G+ bacteria (25%)

· Strep viridans

· beta-haemolytic strep (Strep pyogenes)

· Enterococcus (Strep faecalis)

· G- bacteria (25%)

· E. coli

· Proteus

· Pseudomonas aeruginosa

· increasing incidence of methicillin-resistance

Source of contamination

Sources

From environment

· from operating theatre

· environment

· personnel

· may be

· direct contact

· air-borne

From patient

· from skin

· haematogenous

· respiratory tract

· urogenital tract

· latent source

· reactivation of old infection (eg. childhood osteomyelitis)

Exogenous

· almost exclusive source of bacteria in theatre are people

· vast majority transferred by air (touch much less important)

· concentration of bacteria proportional to activity and number of people

Skin

· wide individual variation in normal flora

· organisms usually in outer 0.3 mm of skin

· usually in sebaceous glands and hair follicles

· Staphylococcus aureus and epidermidis are most important resident skin microbes

· epithelial cells continually lost from skin

· primarily from friction between clothing and skin

· 500 000 shed during undressing

· 5-10% of epithelial cells carry viable bacteria

biomaterials

· biomaterials act as substrates that encourage bacterial adhesion and proliferation

· bacteria compete with host cells for ability to bind to surface

· if bacteria win, adhere to surface and form biofilm

· secrete glycocalyx that further protects bacteria from antibiotics

· causes resistant infection

· infection almost impossible to eradicate without removing prosthesis

Mechanism of adhesion

· attach via three interactions

1. physical forces

· van der Waals forces (physical forces involving particle charges)

· eg. initial attachment of organisms to biomaterial

2. chemical forces

· covalent polar or hydrogen-bonding interactions

· eg. binding of slime polysaccharide to sites on tissue or biomaterial

3. specific receptor binding

· between bacterial receptor surface molecules and protein ligand molecules

· eg. receptor binding of bacteria to fibrinogen already on surface

Prevention

Assessment

· search for potential sites of remote infection and treat if found

· skin (examine)

· respiratory infection (recurrent history, CXR)

· UTI (recurrent history, MSU)

· recognise high-risk patients

· patients with rheumatoid arthritis esp. if on steroids

· decreased immunocompetence

· poor tissues

· other causes of compromise

· diabetes

· alcoholism

· immune deficiency

· malignancy

· old age

Preparation

· preoperative showers

· 3 showers every 8 hrs

· shaving in theatre just prior to surgery

· folliculitis and dermatitis if night before

Surgical technique

· minimise operating time

· handle tissues carefully

· irrigate tissues to mechanically remove bacteria

· use closed suction drains in dead space

Operating environment

· laminar flow

· body exhaust suit

· double gloving

· reduction in theatre traffic

Prophylactic antibiotics

· as discussed below

Results

Charnley

· initial infection rate 9% in 1st 190 hips

· changes to air cleanliness

· laminar flow and body exhaust

· rate reduced to 1.3%

MRC trial

· large multicentre trial in Great Britain

· 1974-1979

· 8000 patients

· environment

· clean air vs ultraclean air vs ultraclean air + body exhaust suits

· antibiotics

· no antibioitics vs prophylactic antibiotics

· results

· control infection rate 3.4%

· decreased to 0.85% with antibiotics and 1.7% with ultraclean air

· additive effect with reduction to 0.4% with both

· reduction to 0.2% with addition of body exhaust suits

· study criticised because of a number of flaws