Sterilization Cycle Failure for Reusable Compounding Equipment
A hospital sterile compounding unit uses a gravity displacement steam autoclave to sterilize reusable stainless steel mixing spatulas and glass beakers. The autoclave log shows a cycle at 121°C for 15 minutes at 15 psi. The biological indicator (BI) from that cycle, a Geobacillus stearothermophilus spore strip, shows growth at 48 hours. The chemical indicator tape changed color, and the autoclave's pressure gauge read 15 psi throughout. The items were wrapped in double muslin and placed in a full load. The unit has a policy of releasing items only after a passing BI. A technician asks whether the items can be used because the chemical indicator passed.
1. Should the items be released for use? Explain the significance of the BI result versus the chemical indicator.
Read the worked answer
No - the items must not be released.
Reasoning:
- BI is the definitive test: A G. stearothermophilus BI is the most reliable indicator of sterilization efficacy. Growth at 48 hours means the cycle did not achieve sterilization, even though the chemical indicator and gauge looked acceptable.
- Chemical indicator limits: Chemical indicators respond to one or more cycle parameters (e.g., temperature or steam) but do not prove microbial kill. A color change only confirms the item was exposed to the process, not that sterilization occurred.
- Gauge limits: A pressure gauge reading does not confirm saturated steam penetration or temperature at the item level.
Correct action: Quarantine the entire load, reprocess the items after investigating the cause, and do not use any item from that cycle.
2. List probable causes of the BI failure and the corrective actions to take before the next cycle.
Read the worked answer
Probable causes:
- Air removal failure: Gravity displacement autoclaves depend on steam displacing air; a full load or improper packing can trap air.
- Overloading or poor packaging: Double muslin wraps that are too tight or a load that is too dense prevent steam penetration.
- Steam quality: Wet steam or superheated steam reduces lethality.
- Cycle parameters: 121°C for 15 minutes may be insufficient for the load size; verify the validated cycle for the load configuration.
- BI handling: Improper incubation temperature or a compromised BI lot.
Corrective actions:
- Quarantine and reprocess the load.
- Review load configuration and packaging; do not exceed validated load size.
- Verify steam quality and autoclave maintenance.
- Re-run a BI with a control and a process challenge device.
- Document the investigation and retraining.
Model answer: Investigate air removal, packaging, steam quality, and cycle validation; reprocess the load and confirm with a passing BI before release.