Sterilisation in Clinical Practice

Also written as Sterilization, Microbial sterilisation.

Sterilisation eliminates all viable microorganisms. Understanding methods, indications, and limitations is vital for infection control, especially where resources are limited.

Overview

Sterilisation is the complete destruction or removal of all forms of microbial life, including bacterial spores. It differs from disinfection, which may leave spores viable.

• Physical method availability (e.g., autoclave, dry heat): Can the facility achieve required temperature/time? – If not, consider chemical sterilisation or referral.

• Essential for surgical instruments, implants, and critical care equipment.
• In low‑resource settings, choice of method balances efficacy, cost, and availability.

Features of the process

Effective sterilisation must reach conditions that inactivate the most resistant organisms (e.g., bacterial spores, prions). Key parameters are temperature, pressure, time, and moisture.

• Biological indicator (spore test): Has sterilisation succeeded? – Growth indicates failure; no growth confirms efficacy.

• Moist heat (steam) at 121 °C for 15 min under 15 psi is standard.
• Dry heat requires 160 °C for 2 h.
• Chemical agents (e.g., glutaraldehyde) need ≥20 min immersion for high‑level disinfection; true sterilisation may need longer exposure.

Transmission and life cycle

Sterilisation interrupts the chain of infection by removing the source of pathogens from medical devices, preventing patient‑to‑patient spread.

• Critical items (surgical tools, endoscopes) must be sterilised before each use.
• Semi‑critical items (laryngoscope blades) may be high‑level disinfected if sterilisation not feasible.

Disease it prevents

Proper sterilisation prevents device‑associated infections such as surgical site infection (SSI), catheter‑related bloodstream infection, and prion disease transmission.

• SSIs increase morbidity, length of stay, and mortality, especially in trauma and obstetric surgery.
• In low‑resource hospitals, outbreaks often trace to inadequate instrument sterilisation.

Diagnosis

When infection occurs despite presumed sterile technique, assess sterilisation process and look for breaches.

• Environmental swab culture: Is there contamination of the sterilisation area? – Positive growth suggests process failure.

• Review sterilisation logs, indicator results, and equipment maintenance records.
• Consider environmental cultures if outbreak suspected.

Treatment and control

Management focuses on source control, appropriate antimicrobial therapy, and reinforcement of sterilisation protocols.

• Antibiotic susceptibility testing: Which pathogen is causing the infection? – Guides targeted therapy.

• Remove or re‑sterilise implicated devices.
• Empiric broad‑spectrum antibiotics pending cultures; de‑escalate based on sensitivities.
• Train staff on proper cleaning, packaging, and cycle monitoring.

Exam pearls

Key points examiners test: distinction between sterilisation and disinfection, appropriate method selection, interpretation of indicator results, and steps when sterilisation fails.

• Moist heat is preferred for heat‑stable instruments; chemical sterilants for heat‑sensitive equipment.
• A failed biological indicator mandates repeat cycle and investigation of cause.
• In resource‑limited settings, validate chemical sterilisation with exposure time and concentration checks.

Questions an examiner may ask

• What sterilisation method would you choose for a heat‑sensitive endoscope in a district hospital? — Explain why moist heat is unsuitable, discuss glutaraldehyde immersion with required exposure time, and note monitoring requirements.
• A patient develops a surgical site infection 3 days after an operation; the autoclave log shows a ‘pass’ but the biological indicator was not used. What should you do? — Highlight need for a repeat cycle, environmental cultures, and empirical antibiotics.
• How does sterilisation differ from high‑level disinfection, and why is this distinction clinically important? — Define each, note that spores survive high‑level disinfection, and relate to risk of SSI.
• In a low‑resource clinic without an autoclave, how can you ensure instrument sterility for minor procedures? — Discuss chemical sterilants, proper concentration, exposure time, and use of boiled water as adjunct.
• What are the consequences of using a sterilisation method that does not achieve the required temperature, and how would you detect this failure? — Explain residual viable spores, use of biological indicators, and visual cues of inadequate steam.
• During a sterilisation audit, you find that instrument packs are damp after the cycle. What does this indicate and how should you act? — Dampness suggests incomplete drying, risk of microbial survival; recommend re‑run cycle or improve drying phase.
• Why are prions resistant to standard sterilisation, and what additional steps are required for neurosurgical instruments? — Mention prion resistance to heat, need for extended autoclave cycles or sodium hydroxide treatment.
• A hospital experiences an outbreak of catheter‑related bloodstream infections. How would you investigate the role of sterilisation? — Review sterilisation logs, indicator results, culture catheter hubs, and assess reprocessing technique.

When to seek help

• Rapidly spreading surgical site infection with systemic signs (fever, hypotension) – urgent surgical review and infection control involvement.

Quick questions

Can alcohol wipes replace sterilisation for surgical instruments?

No; alcohol disinfects but does not kill spores, so it cannot guarantee sterility.

What is the minimum autoclave cycle for sterilising metal instruments?

121 °C for 15 min at 15 psi is the standard minimum.

If a biological indicator fails, what is the next step?

Repeat the sterilisation cycle, inspect the load for packaging defects, and review equipment function before reuse.