Out-of-Tolerance Autoclave Probe After 23 Released Loads
An autoclave used to terminal-sterilize a liquid injectable is calibrated annually. At the 12-month calibration, the reference RTD in the chamber drain reads 0.8 °C lower than the standard at 121 °C. The acceptance tolerance is plus or minus 0.5 °C. The previous calibration was 11 months earlier and was in tolerance. During that interval, 23 loads were released, each with a biological indicator that was negative and each with a recorded F0 above the minimum. The validation package from three years ago identifies the drain probe as the control probe and shows the coldest location at the outer edge of the middle shelf. The site's procedure says any calibration failure triggers a deviation and impact assessment, but the production manager argues that the negative BIs prove sterility and no action is needed beyond recalibrating the probe. The autoclave is now out of service pending repair. No temperature mapping was performed after the last probe replacement six months ago.
1. Assess the impact of the out-of-tolerance calibration on the 23 released loads. What data would you require and what preliminary decision would you make?
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The direction of the error matters but cannot be assumed constant. If the probe reads 0.8 °C lower than the standard, the recorded temperature may understate actual temperature at that point, which would mean greater lethality, not less. However, a single-point calibration failure does not prove the error is linear or that other temperatures are safe. The probe may read high at other points, and the drain probe controls the cycle. The 23 loads therefore need a documented impact assessment rather than a blanket statement that negative BIs prove sterility.
I would require the calibration history and as-found data at multiple temperatures, probe replacement records, the three-year-old validation package, heat-penetration data for each load configuration, load records, F0 calculations, biological-indicator lot and incubation records, and the missing post-replacement temperature mapping. I would also review whether the control probe was the same probe used for release. Preliminary decision: hold further release, do not recall solely on this finding, and initiate a deviation. If the assessment shows the actual load was at least as lethal as validated and the coldest location was covered, release may stand with justification. If not, consider re-sterilization, rejection, or recall.
2. Evaluate the missing temperature mapping after probe replacement and the proposed corrective action of recalibration only.
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Replacing a control probe is a change that can affect the validated state. Temperature mapping after replacement is necessary to confirm the cold spot and the uniformity of the chamber, especially because the validation package is three years old and the probe is the control probe. Recalibration alone restores the instrument reading but does not demonstrate that the loaded chamber still meets the validated heat distribution and penetration requirements. The production manager's proposal is therefore incomplete.
The corrective action should include a deviation, root-cause investigation of why mapping was not performed, and a change-control record for the probe replacement. The site should perform temperature mapping at the qualified load configurations, followed by heat-penetration and biological-indicator challenges. If the mapping confirms the previous cold spot and uniformity, the validation state can be restored with justification. If not, revalidation is required. The CAPA should also update the calibration and maintenance procedure to require mapping after any probe replacement or major repair, with QA approval before release.
3. Define the change control and qualification steps to return the autoclave to service.
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Return to service should follow a defined sequence:
- Containment: keep the autoclave out of service and quarantine affected loads pending assessment.
- Investigation: complete the calibration failure deviation, including as-found data and probe history.
- Repair and calibration: replace or adjust the probe, calibrate against a traceable standard at multiple points, and document as-found and as-left results.
- Change control: approve the probe replacement and any procedure changes before execution.
- Qualification: perform empty-chamber temperature mapping, loaded mapping for worst-case configurations, heat-penetration studies, and biological-indicator challenges.
- Validation review: confirm that F0, uniformity, and cold-spot data meet acceptance criteria.
- Release: QA approves the qualification report and returns the autoclave to service.
- Training and PM: train operators on any revised procedure and update the preventive maintenance plan.
The 23 released loads should be assessed in parallel. The final decision should be documented with a risk rationale, and the CAPA should be verified for effectiveness through the next calibration and mapping cycle.