Sterility & Theatre Protocols

Surgical site infection (SSI) is one of the most common and costly healthcare-associated infections, occurring in approximately 2–5% of surgical procedures and up to 10–15% of orthopaedic implant surgery. The financial, functional, and mortality burden of SSI — particularly prosthetic joint infection (PJI) — is enormous. The theatre environment, sterility protocols, and aseptic technique are the principal weapons against surgical contamination. Every member of the surgical team has individual and collective responsibility for maintaining the sterile field. Understanding the scientific basis, hierarchy, and practical application of sterility measures is fundamental to surgical practice.

• Definitions: (1) Sterilisation — the complete elimination or destruction of ALL forms of microbial life, including bacterial spores; the most stringent level; (2) Disinfection — the elimination of most pathogenic microorganisms (but NOT spores) from inanimate surfaces; high-level disinfection kills all organisms except resistant spores; (3) Antisepsis — the destruction or inhibition of microorganisms on living tissue (skin, mucous membranes); (4) Asepsis — the absence of microorganisms in a defined area; the technique of preventing contamination of the sterile field; surgical asepsis is maintained by a combination of sterilised instruments, sterile gloves/gowns, sterile drapes, and correct team behaviour
• Sources of contamination: the surgical team (hands, shed skin scales — the single most important source of microorganisms in the theatre); the patient`s own skin flora (particularly Staphylococcus aureus, coagulase-negative staphylococci, Propionibacterium acnes for shoulder surgery); the environment (air — viable particles in positive-pressure laminar flow theatres; surfaces; equipment); instruments (poor sterilisation); irrigation and implant-handling

• Chlorhexidine-alcohol vs povidone-iodine (betadine): two RCTs (Darouiche et al. NEJM 2010, and PREPARE trial 2016) established that chlorhexidine-alcohol skin preparation significantly reduces SSI rates compared to povidone-iodine aqueous for most surgical sites; chlorhexidine (2% chlorhexidine gluconate + 70% isopropyl alcohol) is the current recommended skin preparation agent for most orthopaedic procedures; it has a longer residual effect, broader spectrum, and is not inactivated by blood/organic matter as readily as povidone-iodine; povidone-iodine remains preferred for mucous membranes (mouth, vagina, bladder), open wounds, and where chlorhexidine is contraindicated (around the eye)
• Pre-operative skin decolonisation: nasal and skin decolonisation of Staphylococcus aureus carriers reduces SSI; MRSA screening for all elective arthroplasty patients is standard in UK practice; MSSA carriers — nasal mupirocin ointment (5 days pre-operatively) + chlorhexidine body wash (5 days); MRSA carriers — decolonisation + specialist infection control input; nasal carriage of S. aureus is the primary risk factor for staphylococcal SSI in orthopaedics
• Surgical scrub vs alcohol rub: traditional surgical hand scrub (chlorhexidine or povidone-iodine scrub solutions, 3–5 minutes) OR alcohol-based hand rub (ABHR — 1.5 minutes); evidence shows ABHR is as effective as traditional scrub for surgical hand antisepsis; ABHR preferred as it is faster, less drying to skin, and has a longer residual effect; nail pick before first case of the day removes subungual debris; no nail varnish or jewellery

• Conventional plenum ventilation: positive pressure in the theatre relative to the corridor (prevents contaminated air entering); 20+ air changes per hour; fresh filtered air delivered from ceiling vents; particle counts in a conventional theatre: approximately 500–1000 colony-forming units (CFU)/m³; adequate for most general and non-implant orthopaedic surgery
• Ultraclean laminar flow (ULF) ventilation: delivers a unidirectional flow of ultra-filtered air (HEPA — high-efficiency particulate air filter; removes particles >0.3 µm including most bacteria) in a vertical or horizontal laminar sheet over the operating table; particle counts <10 CFU/m³ in the surgical zone; the Charnley-Howorth `greenhouse` (body exhaust suit + laminar flow + antibiotic prophylaxis) is the classical combination for total joint arthroplasty; multiple large series (MRC Hip Arthroplasty Trial, Charnley`s series) demonstrate dramatically lower deep infection rates with ULF + prophylaxis vs conventional theatre; however, the benefit of ULF alone (without exhaust suits) is debated in some modern RCTs
• Body exhaust suits (space suits): full enclosed suit with exhaust ventilation system; the surgeon`s shed skin scales, exhaled breath, and nasal/oropharyngeal flora are captured and extracted within the suit rather than dispersed into the theatre air; further reduces the CFU count in the surgical zone; standard in dedicated arthroplasty theatres at most UK centres; worn with laminar flow for THA and TKA
• Theatre discipline: the single most modifiable source of contamination is human behaviour; minimise theatre traffic (each opening of the door disrupts the positive pressure and introduces contaminated corridor air); keep doors closed during surgery; minimise the number of personnel in the theatre; no talking over the open wound; surgical field should not be reached over (cross-contamination); the scrub nurse should face the sterile field at all times

• Principles of surgical antibiotic prophylaxis: (1) administer within 60 minutes before skin incision (30 minutes for vancomycin and fluoroquinolones — longer infusion time); (2) the antibiotic must cover the most common causative organisms (skin flora — S. aureus, coagulase-negative staphylococci); (3) choose the narrowest-spectrum effective agent to preserve gut flora and prevent C. difficile; (4) repeat the dose if the operation lasts >2 × the antibiotic`s half-life or if blood loss >1500 mL; (5) discontinue within 24 hours of surgery — no benefit beyond 24 hours; (6) the antibiotic must be in the tissue at the time of incision — this is the critical timing requirement
• Standard agents (UK practice): co-amoxiclav (Augmentin) 1.2g IV — broad spectrum, covers Staph/Strep and some Gram-negative organisms; or cefuroxime 1.5g IV for penicillin-non-allergic patients; for MRSA carriers or penicillin allergy — teicoplanin 400mg IV or vancomycin 15mg/kg IV (must start 30–60 minutes before incision); for total joint arthroplasty — co-amoxiclav or cefuroxime remains standard; some centres add gentamicin for high-risk patients (diabetics, revision arthroplasty)
• Antibiotic-loaded cement: in cemented arthroplasty, antibiotic is incorporated into the bone cement (most commonly gentamicin or tobramycin, or combination gentamicin + vancomycin for high-risk cases); the antibiotic elutes from the cement into the surrounding tissue, providing local prophylaxis at concentrations far higher than systemic dosing; commercially available antibiotic-impregnated cements (Palacos R+G, Simplex with tobramycin); routine use in cemented THA and TKA in most UK centres

• Sterilisation hierarchy: sterilisation (kills ALL including spores) > high-level disinfection (kills all except resistant spores) > low-level disinfection (kills vegetative bacteria, fungi, enveloped viruses); autoclaving = gold standard sterilisation for heat-stable instruments
• Autoclave: 134°C × 3 min (porous load) or 121°C × 15 min; kills ALL including spores; biological indicator = Bacillus stearothermophilus; Bowie-Dick test = steam penetration check; cannot use for heat-sensitive items
• EO gas: low-temperature sterilisation; heat-sensitive items; toxic/carcinogenic — long aeration required; used for factory sterilisation of implants; being replaced by hydrogen peroxide plasma (Sterrad) in hospitals
• Gamma irradiation: factory sterilisation of single-use items; damages polyethylene (oxidative degradation) — hence cross-linked polyethylene uses different methods; allograft bone sterilisation
• Chlorhexidine-alcohol vs betadine: chlorhexidine-alcohol significantly reduces SSI (Darouiche NEJM 2010, PREPARE 2016); longer residual effect; not inactivated by blood; preferred for most orthopaedic surgery; betadine preferred for mucous membranes and eyes
• Laminar flow: ultraclean laminar flow (ULF) + body exhaust suits + prophylaxis = Charnley triad for arthroplasty; reduces deep infection from ~3.5% (conventional) to <0.5% in Charnley`s series; HEPA-filtered unidirectional air; <10 CFU/m³ in surgical zone
• Antibiotic prophylaxis: within 60 min of incision; antibiotic must be in tissue AT the time of incision; repeat if operation >2× half-life or blood loss >1500 mL; stop within 24 hours (no benefit beyond 24 hours); co-amoxiclav or cefuroxime; vancomycin/teicoplanin for MRSA carriers or penicillin allergy
• Theatre discipline: most modifiable contamination source = human behaviour; minimise door openings (each opening disrupts positive pressure); no talking over open wound; minimise theatre traffic; scrub nurse faces sterile field; body exhaust suits capture shed skin scales and exhaled flora
• MRSA decolonisation: nasal mupirocin (5 days) + chlorhexidine body wash (5 days) for MSSA/MRSA carriers before elective arthroplasty; screen ALL elective arthroplasty patients pre-operatively; decolonisation reduces staphylococcal SSI rates significantly