Sterilisation and Operating Theatre Discipline
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Direct answer
Steam at 121 degrees Celsius under 15 pounds per square inch for 15 minutes kills every form of microbial life including spores — that single autoclave setting sterilises the wrapped instruments of every operating theatre and dental clinic, with a high-vacuum alternative of 134 degrees for 3 minutes for heat-stable loads. Sterilisation (destruction of all microorganisms including spores) is distinguished from disinfection (elimination of most pathogenic organisms, spores spared) and antisepsis (the same on living tissue), and the level required follows the instrument's intended contact — critical instruments entering tissue must be sterile, semi-critical need high-level disinfection, non-critical contact intact skin. What separates a safe theatre from a dangerous one is not the machine but the monitoring: chemical indicators on every pack, the Bowie-Dick test for vacuum autoclaves daily, and spore strips of Geobacillus stearothermophilus weekly, with a central sterile supply department moving instruments in one direction only, from dirty to clean to sterile to store.
What you must remember
- Definitions in hierarchy: cleaning removes soil (always first), disinfection kills vegetative organisms but not all spores, sterilisation kills all including spores — an unwashed instrument cannot be sterilised, because organic matter shields microbes.
- Moist heat benchmarks: autoclave at 121 °C, 15 psi, 15 minutes (holding time) for wrapped loads; 134 °C, 30 psi, 3 minutes in high-vacuum (class B) autoclaves — the parameters dental surgery instruments and theatre linen rely on; steam under pressure beats dry heat because protein denaturation is faster in moisture.
- Dry heat and its niche: 160 °C for one hour (holding) for oils, powders, glass and sharp instruments that steam dulls — slower because air conducts poorly.
- Chemical methods: 2 per cent glutaraldehyde solution gives high-level disinfection in about 20-45 minutes and sterilisation after roughly 10 hours of immersion for heat-sensitive endoscopes; ethylene oxide gas sterilises heat- and moisture-sensitive plastics at low temperature; hydrogen peroxide plasma is the modern low-temperature alternative.
- Filtration and radiation: membrane filters sterilise heat-labile fluids; gamma irradiation sterilises single-use disposables at the factory.
- Monitoring trinity: chemical indicators or autoclave tape on each pack (parameters met), Bowie-Dick test daily for pre-vacuum autoclaves (air removal adequate), and biological indicators — Geobacillus stearothermophilus spores — weekly and after repairs (spores actually killed); never accept an unlabelled, undated pack.
- CSSD and theatre discipline: unidirectional flow from receiving and washing through packing, sterilising, sterile store to issue; theatre etiquette of masks, scrubs, traffic control and door discipline; event-related sterility means a pack is sterile until its barrier is breached, with shelf-life dating now quality-linked rather than purely calendar-linked.
From dirty tray to sterile tray: the journey of a forceps
Follow an extraction forceps through a day. It returns to central sterile supply soiled with blood and saliva — first, immediate rinsing and ultrasonic or manual cleaning with an enzymatic agent, because residual organic load is the commonest cause of sterilisation failure. It is inspected (hinges, alignment, rust), then packed in a porous-wrap or pouch with a chemical indicator inside and out, dated and initialled. The pack rides the autoclave cycle chosen for the load; the indicator transforms colour, and the cycle printout is checked before the pack goes to the sterile store. On the morning of surgery it is opened only after the outer wrap is verified dry, intact and in-date — a wet pack is a contaminated pack, because moisture wicks organisms through the wrap. Handpieces and other lumened dental instruments need a class B vacuum autoclave precisely because trapped air in narrow lumens defeats a simple gravity cycle. If a spore test fails that week, the machine is pulled from service, loads since the last negative test are recalled where possible, and the failure is investigated before release. Every step exists because one skipped step is invisible at the time and unmistakable in the wound after.
How the exam frames it
BDS papers ask for the classification of sterilisation methods (physical versus chemical, with examples of each), the autoclave parameters by number — 121 °C, 15 psi, 15 minutes is probably the single most repeated figure in Indian surgical viva history — and the differences between disinfection and sterilisation with clinical examples. Objective questions test the indicators: which organism is used in biological monitoring, what the Bowie-Dick test detects, why glutaraldehyde and not autoclave for a flexible endoscope. The clinical viva scenario — a heat-sensitive instrument, an implant, a soiled instrument — expects you to choose a method with a reason, not recite the whole list.
Frequently asked questions
What are the standard autoclave parameters for wrapped instruments?
Holding at 121 °C at 15 psi for 15 minutes, or 134 °C at 30 psi for 3 minutes in a high-vacuum cycle — the numbers examiners expect verbatim.
How does disinfection differ from sterilisation?
Disinfection eliminates most pathogenic microorganisms but not necessarily spores, whereas sterilisation destroys all forms of microbial life including spores, yielding an absolute state.
Which spore-forming organism is used in biological indicators?
Geobacillus stearothermophilus spores, among the most heat-resistant, are incubated after the cycle; growth means sterilisation failure.
Why must instruments be cleaned before sterilisation?
Organic soil shields microorganisms from steam and chemical contact, inactivates disinfectants and fixes onto surfaces when heated — cleaning is the rate-limiting step of the whole chain.
How are heat- and moisture-sensitive instruments sterilised?
By low-temperature methods — ethylene oxide gas or hydrogen peroxide plasma — or prolonged immersion in 2 per cent glutaraldehyde for high-level disinfection of endoscopes.