• What is surgical infection?
• Pathogenesis
• Spread of surgical infection
• Sepsis, Bacteraemia & Septicaemia
• Diagnosis
• Treatment

Nosocomial infection & infection control

• (Wound infection)
• Prophylactic antibiotics

Specific types of surgical infection

• Wound infection
• Furuncle & carbuncle
• Cellulitis
• Myositis (localised & spreading)
• Necrotising fasciitis

Principles of Antiobiotic Therapy

A surgical infection is an infection that

1. Unlikely to respond to non-surgical treatment (it usually must be excised or drained)
2. Occupies an unvascularised space in tissue (e.g. appendicitis, empyema, gas gangrene and abscesses)
3. Occurs in an previously operated/ trauma site

Three common elements

1. Infectious agent
2. Susceptible host
3. Closed unperfused space

Host's body defence mechanisms vs. bacteria in the environment (body surface, GIT)

Aerobic

• Gram positive: streptococci, staphylococcus aureus
• Gram negative: E. coli, klebsiella, pseudomonas

Anaerobic: bacteroides (low/ absent oxygen)

• Opportunistic: pseudomonas, fungi etc (infection cause by bacteria that is normal flora in healthy individual); esp. in nosocomial infection
• Community-acquired vs. hospital-acquired (nosocomial): more virulent/ resistant to Tx in nosocomial

Body defence mechanism

• Local defence mechanism: skin, mucous membrane, cilia, GIT (compromised in (1) Trauma (2) Viral infection - makes surface inflamed and more permeable)
• Specific immunity: cell mediated and hormonal mediated
• Non-specific immunity: white cells (phagocytes, macrophages)

Immunosuppressed host

• Immunodeficiency disorders: acquired, congenital
• Burn, trauma
• Chronic disease: DM, CRF, cirrhosis liver
• Malignancy
• Iatrogenic: steroid, cytotoxic agent (kill BM cells as well as ca cells)

• Poorly vascularised place in tissue (wound)
• Natural space

1. Entry of micro-organisms into the body
2. Apposition to the host cell
3. Overcoming local defences
4. Accumulation & spread
5. Outwitting the immune response;
6. Inducing cellular injury - the manifestation of disease: fever, leukocytosis, specific acute phase proteins;
7. Persistence

• Spread along anatomically defined paths
• Eg. Clostridial myonecrosis (through muscle plane), necrotising fasciitis (bacteria kills fascia and spreads along fascia, not limited to one plane), cellulitis (through subcutaneous plane)

• Accumulation of dead WBC causing pus - exerts pressure on surrounding body tissue
• Breaching of natural boundary -> fistulas or sinuses

• Phlegmon: diffuse inflammation of the soft or CT due to infection
• Oedema
• Superficial infection - eg. Cellulitis

• Lymphangitis: streptococcal

• IV drug abuse: empyema, endocarditis
• Brain abscess, liver abscess

• Bacteria in blood
• Transient bacteraemia: usually of no clinical significance except in patients with prosthesis or RHD (bacteria reside prosthesis/ damaged heart valves -> IE)

• A serious infection resulting from both bacteraemia and toxaemia (bacterial toxins in blood)
• Gram -ve: endotoxin (eg. E Coli) ® peripheral dilatation, increased cellular permeability
• Systemic inflammatory response syndrome (SIRS)

1. Pyrexia (> 38⁰C) or hypothermia (< 36⁰C)
2. Tachycardia (hypotension)
3. Tachypnoea
4. Leukocytosis: increase WBC (>12) or leucopenia (<4)

• Sepsis = SIRS + Documented source of infection
• Severe sepsis = Sepsis + Dysfunction of one or more organs (liver, kidney, intestine, lung, heart; multiple organ failure = high mortality; may remove infective source but Pt dies due to organ failure)

• Aim of investigation: ID source of sepsis

• Limited use: cannot tell source, can only tell if sepsis is present
• WBC
• Blood gas analysis: metabolic acidosis
• Coagulation profile: impairment of coagulation due to stimulation of body's coagulation system

• Blood culture : the best evidence of sepsis (aerobic & anaerobic cultures)

• CXR: chest infection (also bone + jt swelling = jt infection)
• CT (Dx, anat location) + US (liver, children/ thin adult for appendicitis)
• Radionucleide scan: eg. WBC scan, attach isotope to WBC (injection), scan few hours later, shows WBC going to area of infection

• Principle of Tx: any septic focus amenable to surgical therapy should be excised or drained

• Superficial abscess: surgical drainage (MUST drain abscess - oedema, tender, erythema, fluctuation); if no surrounding cellulitis, do not need ABX
• Deep abscesses: CT or ultrasound guided percutaneous catheter drainage; surgical drainage (then Tx with ABX, can change abscess from emergency to elective need for operation)
• If very obese, in bowel, use CT (difficult to localise with US)
• Eg. Cholecystitis (remove gallbladder); Appendicitis (remove appendix); Colonic diverticulitis (remove that part of the colon)

• Eg. Appendectomy, cholecystectomy etc
• Elective excision: prevent recurrence (eg. Cholecystitis with gallstones, if no cholecystectomy, then Pt will present later with another attack)
• Appendicitis: cannot treat with ABX, need appendectomy
• Many times use both excision and ABX (eg. cholecystitis: usually only need cholecystectomy and no ABX, but if severe infection need to have cholecystectomy and ABX)

• Not necessary for simple surgical infections that respond to incision and drainage alone (eg. furuncles and uncomplicated wound infection)
• Infections likely to spread or persist require antibiotic therapy
• Empirical treatment à definitive treatment according to culture result

• Esp. if Pt already septic ® IV fluid, nutrition, circulatory support (inotropes) etc.

• Nosocomial infection = Hospital acquired infection: surgical team, operating room, bacteria harboured by patient before operation

• Operating room attire: caps, mask, gown & gloves
• Surgical behaviour (1) Aseptic operating technique (2) Cutaneous or respiratory infection (3) Hand scrubbing
• Hand washing: mandatory after all contact with infected patients

• Design of operating room: e.g. ventilation (+ve pressure in OT)
• Sterilisation of equipment and instrument

• Treat pre-existing infection before elective operation
• Skin commensals (1) Preoperative showers or baths (2) Body hair: prefer clipping because shaving causes microcuts; immediately before operation (3) Skin included in operating field: antiseptic cleansing
• Universal precautions: any procedure involving close contact with any patient or patient's body fluid (blood, urine, faeces or saliva) should be performed by personnel wearing gloves or other protective devices

• Aim: to reduce surgical wound infection

• Use "first-line" antibiotics to reduce emergence of resistance strain
• Consider cost-effectiveness, efficacy and safety
• Eg. (1) Urological operation: according to urine culture (2) Colorectal operation: gram negative aerobes and anaerobes (3) Prosthetic placement: staphylococcus aureus

• Not indicated for clean operation like hernia repair (except placement of prosthesis or patient with rheumatic heart disease or prosthetic heart valve)

• To achieve a therapeutic level in the blood and tissue before surgical incision
• Intravenous: amount varies with body type of Pt
• Less than 2 hours before operation: at induction of anaesthesia

• Stopped a few hours after operation
• Prevent resistant strains emerging

• Due to bacterial contamination during/ after a surgical procedure (usu. only subcut tiss)
• Risk µ wound class (usu. day 5-10 post-op)
• Clinical features: fever, wound pain, oedema, erythema, discharge

1. Clean (hernia repair, sebaceous cyst) 1.5
2. Clean contaminated (elective cholecystectomy, cholectomy with time for bowel preparation) 7.7
3. Contaminated (perforated appendix, bowel obstruction needing emergency cholectomy with now time for bowel preparation) 15.2
4. Dirty (LI bowel perforation - faeces inside peritoneal cavity) 40.0

• Abdominal operation
• Operation > 2 hours (­ difficulty, ­ planes opened, ­ bacterial exposure)
• Contaminated operation
• ³ 3 pre-existing medical conditions

• Careful operative technique
• Reduction of contamination: eg. Clean large bowel before operation
• Prophylactic antibiotics
• Contaminated wound: delayed primary closure or secondary closure (eg. Delayed primary: if leave open, clean for few days and then suture again; Delayed secondary: if leave open, clean, leave to heal without sutures)
• Treatment: open the wound for drainage; wound swab

• Furuncle: infected hair follicles
• Carbuncles: starts @ furuncles, spread through dermis/ subcut tissue in a myriad of connecting tunnels; freq. back of neck (strong aponeurosis, if open there are pockets of pus, therefore cannot do incision and drainage, therefore need excision); poorly-controlled DM (need control to prevent recurrence)
• Organisms: staphylococci & anaerobic diphtheroids
• Treatment (1) Furuncle: incision & drainage (do not need ABX) (2) Carbuncles: excision & antibiotics

• Common invasive non-suppurative infection of connective tissue (no fluctuation)
• Usually caused by streptococci
• Clinical finding (1) Erythematous, oedematous skin (2) May cause lymphangitis
• Treatment (1) Rest, elevation, packs (2) ABX

• Types (1) Localised (2) Diffuse
• Organisms (1) Staphylococcus aureus (2) Clostridium (gas gangrene)
• Gas Gangrene: (1) < 3 d after inj (2) Rapidly increasing wound pain (3) Oedema (4) Purulent exudate (5) Crepitus: gas inside tissue (6) Profound toxaemia (7) Extensive underlying muscle necrosis: compartment syndrome
• Treatment (1) Extensive surgical debridement: cut muscle away, amputation (2) Hyperbaric oxygen: organisms relatively anaerobic (3) ABX: usu. Tx combination
• MUST have debridement with ABX (hyperbaric oxygen if facilities allow)

• An invasive infection of fascia
• Usually caused by multiple pathogens (1) Microaerophilic streptococci (2) Staphylococci (30 Gram-negative bacteria: klebsiella, pseudomonas (4) Anaerobes: bacteroides (5) Clostridium
• Pathogenesis: infectious thrombosis of vessels passing between skin and deep circulation -> skin necrosis as well as necrosis of underlying fascia and subcutaneous tissue
• Clinical features (1) Skin: haemorrhagic bullae (2) Fascial necrosis: usually wider than the skin appearance indicates (3) Crepitus (4) Toxic patient
• Treatment (1) Surgical debridement: remove all avascular skin and fascia; may require repeated debridement (2) ABX: broad-spectrum (3) Circulatory support: blood or plasma transfusion

• Surgeon decides ® clinical impression, that a microbial infection probably exists

• A guess as to which microorganisms are most likely to cause the suspected infection
• Based on clinical grounds: the suspected type of infection; known types of organisms involved and local pattern

• Relevant culture should be taken (blood, sputum, urine etc) before start of treatment to provide a microbiological diagnosis
• Culture not helpful after start of empirical ABX
• May have atypical organisms involved

• Selects the drug that is most likely to be effective against the suspected organisms ("empirical" therapy)
• Because culture result will require a number of days to be available and treatment cannot be delayed till availability of result
• Choice: depends on local antibiotics sensitivity pattern
• Can be single agent (against one organism or broad-spectrum antibiotics against a wide spectrum of organisms) or combined agents (against both aerobic and anaerobic organisms)
• In principle: should be specific; avoid overuse of broad-spectrum antibiotics except in life-threatening situation (to reduce emergence of resistant strains)

• Make sure that the drug can reach the site of active infection in adequate concentration
• Types of drug used (different route of administration): depends on pharmacological properties
• Whether patient can eat (if so, use oral preparation)
• Life threatening infection: require intravenous route to ensure very high blood level of antibiotics

• Usually calculated according to body weight
• Some drugs, e.g. aminoglycoside, serum drug level can be checked
• Adjusted (1) Children (2) Liver impairment (3) Renal impairment - drugs excreted through kidneys: may need adjustment of dosage in patients with renal impairment or failure

• Determined in part by clinical response and past experience and in part by laboratory indications of suppression or elimination of infection
• Example: subsidence of fever; negative culture
• A course of antibiotics: five to seven days (longer with fungal infection)

• Required when:

1. Clinical response: no clinical response to initial empirical therapy; may no longer need ABX if no need for; inotropes for circulatory support, etc. (most commonly used indication)
2. Culture results indicate resistance of microorganisms to antibiotics used and evidence of persistence of infection (no need to change antibiotics if good clinical response) (good in complicated situations: > 1 organism)