Biological indicator failure after a gasket replacement: releasing or withholding surgical sets
A 250-bed railway divisional hospital runs a central sterile supply department with two horizontal autoclaves: one for wrapped goods at 121 degrees C for 30 minutes, and a prevacuum unit at 134 degrees C for 4 minutes. On Monday the door gasket of the prevacuum unit was replaced by the engineering section and the unit was put back into service the same afternoon without any revalidation. The evening load contained 14 laparotomy packs, 6 minor procedure sets and 4 implant boxes of orthopaedic screws. Packs were wrapped in two layers of 100 per cent cotton, loaded three high with the chamber about 95 per cent full, and several packs touched the chamber wall. On Wednesday the weekly biological indicator (Geobacillus stearothermophilus spore strips incubated at 56 degrees C) from that load showed growth, and the unexposed control also showed growth. All chemical indicators in the load had changed colour. Two of the laparotomy packs were already used on Tuesday for an emergency caesarean section, and the orthopaedic implant boxes are booked for Thursday's elective list. The theatre superintendent asks whether the remaining sets may be used tomorrow.
1. What is your immediate decision about the remaining sets and the implants, and what actions follow from the two packs already used?
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Do not release any item from that load, including the implants, and do not use them for Thursday's list.
Immediate actions, in order:
- Quarantine all remaining items from the load - the 12 unused laparotomy packs, the 6 minor sets and all 4 implant boxes - physically segregated and labelled 'do not use, sterilisation failure'.
- Implants are held until a biological indicator is negative. There is no exception for implants; a flash cycle or a chemical-indicator-only release is not acceptable. Thursday's elective list must be postponed, re-supplied from a validated cycle, or re-sterilised and held again.
- The two packs already used cannot be recalled. Raise an incident report, inform the infection control committee and the operating surgeon, and place the caesarean patient under surgical site infection surveillance with a documented note in her file. She is not automatically started on antibiotics; she is watched.
- Inform the CSSD in-charge and the medical superintendent, and log the failure with the load number, autoclave ID and cycle parameters.
The key judgement: a positive biological indicator overrides every chemical indicator in the load. Chemical indicators show that the pack was exposed to steam - not that it was sterilised.
2. What are the likely causes of the failure, and how would you investigate them?
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Work from the most probable and most recent change outwards:
- The gasket replacement is the prime suspect. A prevacuum autoclave returned to service without revalidation can leak air into the chamber, so air removal is incomplete and steam cannot penetrate the packs. Check the gasket seating, door alignment and leak rate; run a Bowie-Dick test, which is the specific test for air removal and steam penetration in prevacuum cycles.
- Loading practice. A chamber 95 per cent full, packs stacked three high and touching the chamber wall impedes air removal and condensate drainage. Recommended loading is around 75 to 80 per cent, packs on edge, not touching walls, with space between them.
- Pack construction. Two layers of cotton is acceptable, but over-tight or oversized packs resist steam penetration; check pack size and weight against local policy.
- Steam and water quality, and the physical record of the cycle (temperature, pressure, time) - a cycle that met parameters but still failed the BI points to air removal rather than steam supply.
- Indicator handling. The control grew, so the incubator and strips behaved correctly and the failure is real, not a false positive.
Document each check and its result; the investigation report, not just the repair, is what prevents recurrence.
3. What criteria must be met before the prevacuum unit is returned to routine use?
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Return to service only on evidence, never on the basis that the gasket 'looks fine':
- Engineering verification of the repair, including a leak-rate test and door-seal check.
- A passing Bowie-Dick test on the first cycle of the day, every day, for prevacuum units.
- Three consecutive biological-indicator-negative cycles, each with its own unexposed control incubated alongside, plus physical parameter records within specification.
- Only then resume routine loads; implant loads continue to be held until the BI is read as negative, and flash cycles are never used for implants.
The pharmacist or microbiologist should also insist on two process changes: a written revalidation rule that any repair to the chamber, door, gasket or vacuum system removes the unit from service until it is revalidated, and retraining of loading staff with a posted loading diagram. Record the return-to-service date, the three BI results and the Bowie-Dick results in the autoclave log so that the next load can be traced to a validated machine.