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Introduction

This paper sets out the critical process parameters for steam sterilisers and bedpan washer-disinfectors, and quantifies the loss of microbial lethality caused by deviations in temperature, pressure, time, air removal and cleaning. It identifies the common causes of deviations and defines the detection, release and recall controls required by AS 5369:2023.

Process Requirements

Regulatory Basis: AS 5369:2023 superseded AS/NZS 4187:2014 and AS/NZS 4815:2006. Hospitals and day procedure services are assessed against Action 3.17 of the National Safety and Quality Health Service (NSQHS) Standards. Australian Commission on Safety and Quality in Health Care Advisory AS24/01 requires a gap analysis against AS 5369:2023 and a compliance plan. Steam sterilisation processes are validated to ISO 17665 and washer-disinfectors to the applicable part of ISO 15883. Terminally sterilised devices require a sterility assurance level (SAL) of 1 in 1,000,000.

Steam Sterilisers: AS 5369:2023 lists common holding times of 121 deg C [250 deg F] for 15 min, 126 deg C [259 deg F] for 10 min, 132 deg C [270 deg F] for 4 min and 134 deg C [273 deg F] for 3 min. Add the equilibration time measured at performance qualification (PQ) to the holding time. Throughout the holding time, the measured chamber temperature and the saturation temperature calculated from chamber pressure must both be within the sterilisation temperature band. Saturated steam at 134 deg C [273 deg F] is at 304 kPa absolute, or 203 kPa gauge [29.4 psig]. At 121 deg C [250 deg F] it is at 205 kPa absolute, or 104 kPa gauge [15.0 psig].

Washer-Disinfectors: A0 is the equivalent time in seconds at 80 deg C [176 deg F] with a z value of 10 deg C [18 deg F]. Bedpan washer-disinfectors to ISO 15883-3 must deliver an A0 value of at least 60, equal to 80 deg C [176 deg F] for 1 min. AS 5369:2023 lists A0 600 holding times of 90 deg C [194 deg F] for 1 min and 80 deg C [176 deg F] for 10 min. ISO 15883-1 guidance gives A0 3000, equal to 90 deg C [194 deg F] for 5 min, for items that could be contaminated with heat-resistant viruses such as hepatitis B. Thermal disinfection at these values is not sporicidal. Bacterial spores, including Clostridioides difficile, are controlled by removal during cleaning.

Failed Cycles: A cycle that does not meet its specification is a failed cycle. Check the process record before release, and quarantine any load from a failed cycle. Do not release a load on calculated lethality when any parameter is outside its specified limit.

Steam Steriliser Parameters

Bedpan Washer-Disinfector Parameters

Causes of Parameter Deviations

• Operator Error: Incorrect cycle selection, overloading, incorrect packaging, interrupted cycles and ignored alarms. Assign cycles by load type, post loading diagrams at each machine, and assess operator competency at defined intervals.

• Inadequate Cleaning: AS 5369:2023 states that a device must be clean for disinfection and sterilisation to be effective. Residual blood, tissue and faecal soil shield microorganisms from steam and hot water. Causes include delayed processing, blocked spray nozzles, low spray pressure and dosing faults.

• Equipment Faults and Calibration Drift: Heater or steam supply faults, valve leakage, door seal leakage and sensor drift. A drifted sensor can report a compliant cycle that was not delivered. Carry out planned preventive maintenance, recalibrate at intervals not exceeding 12 months, and run the daily steriliser tests before first use.

• Load Configuration: Excess mass, dense packs and lumened devices extend equilibration time and impede air removal. Do not exceed the load mass and configuration validated at PQ, and requalify before introducing new devices or configurations.

• Delayed Processing: Soil that dries on bedpans and instruments resists removal in a standard cycle. Process bedpans immediately after use. Do not pre-rinse with hand-held spray hoses, which generate splash and aerosol.

• Chemical Supply: Empty or incorrect detergent removes the chemical contribution to soil removal. Check levels daily, act on low-level alarms and verify dose volumes quarterly.

• Utilities: Poor steam quality, low water pressure, hard water and power interruptions cause temperature, pressure and cleaning deviations. Include utilities in the risk assessment and in fault investigation.

Effect of Deviations on Lethality

Kinetics: Thermal inactivation is logarithmic. The D value is the time to reduce a population tenfold at a stated temperature. The z value is the temperature change that changes the D value tenfold. F0 is the lethality of a steam process expressed as equivalent minutes at 121.1 deg C [250 deg F] with z equal to 10 deg C [18 deg F]. With this z value, each 3 deg C [5.4 deg F] shortfall halves lethality and each 10 deg C [18 deg F] shortfall reduces it tenfold. Lethality is proportional to time, so halving the holding time halves it.

Worked Example: Steam process biological indicators to ISO 11138-3 use Geobacillus stearothermophilus spores with a D value at 121 deg C [250 deg F] of not less than 1.5 min. At z equal to 10 deg C [18 deg F], the D value is about 4.5 s at 134 deg C [273 deg F] and about 18 s at 128 deg C [262 deg F]. A 3 min hold therefore delivers about 40 log reductions at 134 deg C [273 deg F] but about 10 at 128 deg C [262 deg F]. A 6 deg C [10.8 deg F] shortfall removes three quarters of the design lethality and the overkill margin on which the process validation depends.

Air and Steam Quality: Air and non-condensable gases insulate surfaces and prevent condensation. In packs and lumens, local temperature can remain below the band while the chamber sensor reads correctly. Superheated steam does not condense until it cools to saturation and transfers heat at a lower rate. These faults produce localised under-processing that the chamber record does not show, so the daily air removal test and the leak rate test are the primary controls.

Organism Resistance: Bacterial spores are the most resistant conventional organisms to moist heat, which is why steam processes are validated with spore indicators. Vegetative bacteria, including Staphylococcus aureus, enterococci and Gram-negative bacteria, together with fungi and most viruses, are inactivated at thermal disinfection A0 values. Heat-resistant viruses such as hepatitis B require higher A0 values. Thermal disinfection does not inactivate bacterial spores, so a cleaning failure in a bedpan washer-disinfector leaves Clostridioides difficile spores on the item. AS 5369:2023 excludes devices potentially contaminated with transmissible spongiform encephalopathies, e.g. Creutzfeldt-Jakob disease. Follow the national guidelines for these devices.

Recontamination: Wet packs, damaged sterile barriers and devices placed on wet or dirty surfaces after processing are nonconforming, regardless of the cycle record.

Detection, Release and Recall

Release: Check the process record against the specification before release from each process. For steam sterilisation with drying, the cycle record must confirm the parameters established at PQ, external chemical indicators must show the specified colour change, packs must be intact with no visible moisture, and any biological indicator, process challenge device or data logger results must be correct. For thermal disinfection, items must be visually clean and dry and the cycle record must conform to the specification.

Failed Cycle: Quarantine the load, reprocess it, and record the deviation and its root cause. Remove the machine from service where the fault could affect device quality. Repeat OQ after repair and requalify where the repair could affect the process.

Recall: Where evidence of process failure is found after release, recall the affected devices promptly. Traceability to the individual cycle and steriliser identifies every device in the affected load. The recall report must identify the circumstances, reconcile recalled quantities, identify affected patients and their follow-up, and record the root cause, corrective action and preventive recommendations.

Infection Surveillance: Notify the infection prevention team of every recall so that affected patients can be followed up. Where a cluster of infections with the same or an unusual organism occurs among patients treated in the same period, review the reprocessing records for the cycles concerned.

Electronic Records: Specify tracking systems that hold a load automatically when a recorded parameter is outside its limit, and that link each device set to its cycle record and release.

Key Actions

• Control Parameters: Run only validated cycles. Hold temperature within the band for the full holding time plus equilibration time, and deliver the specified A0 in washer-disinfectors.
• Release on Specification: Release only when every parameter is within its limit. Never release on calculated lethality outside the specification.
• Test and Calibrate: Run the daily air removal test and the specified leak rate tests. Recalibrate at intervals not exceeding 12 months and requalify at least annually.
• Clean First: Verify cleaning action, detergent dosing and loading, because thermal disinfection does not inactivate spores.
• Train and Assess: Train every operator and assess competency at defined intervals.
• Trace and Recall: Maintain traceability to the cycle and a documented recall procedure, and notify infection prevention of every recall.

References

1. Standards Australia. AS 5369:2023 Reprocessing of reusable medical devices and other devices in health and non-health related facilities.
2. Australian Commission on Safety and Quality in Health Care. Advisory AS24/01 Requirements for reprocessing of reusable medical devices in health service organisations.
3. ISO 17665:2024 Sterilization of health care products, Moist heat.
4. ISO 15883-1 Washer-disinfectors, Part 1: General requirements, terms and definitions and tests.
5. ISO 15883-3 Washer-disinfectors, Part 3: Requirements and tests for washer-disinfectors employing thermal disinfection for human waste containers.
6. ISO 11138-3 Sterilization of health care products, Biological indicators, Part 3: Biological indicators for moist heat sterilization processes.
7. EN 285 Sterilization, Steam sterilizers, Large sterilizers.