A veterinary autoclave that is not monitored is a sterility assumption, not a sterility guarantee. The 2018 AAHA Infection Control, Prevention, and Biosecurity Guidelines are explicit: "Biological indicators [should be] periodically used to ensure adequate sterilization, and results recorded in a log" and "quality control sterility indicators [should be] included in each autoclaved pack." Without a written maintenance log and a biological-indicator testing program, a practice has no defensible evidence that any surgical instrument was sterile — and no way to trace a surgical-site infection back to a failed cycle.

This article provides a complete autoclave maintenance and monitoring workflow for a general veterinary practice. It covers the three tiers of sterilization monitoring (mechanical, chemical, biological), the log structure that survives an AAHA evaluation or a state board inspection, the failed-cycle response protocol adapted from CDC guidance, and the staff-ownership model that keeps the system running.

The three monitoring tiers

Every sterilization authority — CDC, AAMI, AAHA — recognizes three tiers of monitoring. All three must be documented.

Chemical indicators tell you the pack was exposed to heat. Mechanical indicators tell you the machine said it reached temperature and pressure. Only biological indicators (BI), also called spore tests, confirm that the conditions were sufficient to kill the most resistant organisms. CDC's Guidelines for Disinfection and Sterilization in Healthcare Facilities state: "Because the spores used in biologic indicators are more resistant than the common microbial contaminants found on patient-care equipment, a negative spore test indicates that other potential microorganisms in the load have been killed."

Biological indicator testing: what to use and how often

Spore selection

For steam sterilization (the method used in virtually all small-animal veterinary clinics), the test organism is Geobacillus stearothermophilus. This spore is used to monitor steam, hydrogen peroxide gas plasma, and liquid peracetic acid sterilizers, per CDC.

Two formats dominate veterinary practice:

• Self-contained vials (e.g., 3M Attest, Tuttnauer Biological Indicators). The spore strip and growth medium are sealed in a single plastic vial. After the cycle, you crush the inner ampule to release the growth medium, then incubate. No mail-in step. Results in 24–48 hours depending on the system. This is the faster, more practical option for most clinics.
• Mail-in spore strips. Paper strips inoculated with spores are run through the cycle and mailed to a third-party lab for incubation and reporting. This is slower — results may take a week — and the strip can be lost or damaged in transit. Woodhouse Laboratories' SporeAlert and similar services provide pre-paid mailers and compliance documentation.

Testing frequency

CDC notes there is no separate recommendation for sterilizers used part-time: "CDC recommends that dental health care personnel monitor sterilizers at least weekly." The same principle applies to veterinary practices with lower surgical volume.

Placement

Place the biological indicator in the most challenging location in the chamber — typically the bottom rack near the drain, in the center of a load. Follow the BI manufacturer's instructions for placement. If the clinic runs multiple autoclaves, test each unit separately and label each BI with the date and autoclave identifier.

The autoclave log: what to record for every load

Per-load record

Every sterilization cycle should generate a row in the autoclave log. The CDC's sterilization monitoring guidance and the AAHA ICPB Guidelines both require that records be maintained for accountability and to enable tracking and reprocessing of affected loads in the event of a failure.

Retention

The FAU Comparative Medicine SOP for biological indicator processing recommends retaining autoclave log sheets for at least one full year, with older logs archived. Some state veterinary boards and accreditation bodies require longer retention — check your jurisdiction. Records must be available for inspection by accreditation agencies (AAHA, state veterinary board) and, where applicable, IACUC or institutional biosafety committees.

Chemical indicators: inside and outside every pack

CDC guidance distinguishes two roles for chemical indicators:

• External indicators (Class 1): Applied to the outside of every pack. They confirm the pack was exposed to the sterilization process — a quick visual check that the pack went through the cycle. If the external indicator has not changed color, the pack has not been processed.
• Internal indicators (Class 5 integrating indicators): Placed inside the pack, typically in the center of the instrument tray or the most difficult-to-sterilize location. They confirm that the sterilizing agent penetrated the packaging and reached the instruments inside. Inspect the internal indicator immediately when opening the pack; if the correct color change did not occur, do not use the instruments.

Chemical indicators do not replace biological indicators. A chemical indicator confirms exposure; a biological indicator confirms kill. Both are needed.

Failed-cycle response protocol

The CDC's Table 12 — "Suggested protocol for management of positive biological indicator in a steam sterilizer" — provides the authoritative step-by-step. Here is the protocol adapted for veterinary practice:

Step 1: Confirm the result

Do not assume the autoclave is broken. A single positive (failed) spore test may be a random event or operator error. Check the mechanical indicators (time, temperature, pressure) for the cycle in question. Check the chemical indicators for that load. If mechanical and chemical indicators suggest proper function, the positive BI may not indicate sterilizer malfunction.

Step 2: Repeat the BI test immediately

Run another biological indicator through a normal cycle. Use a BI and a control from the same lot number. Incubate both.

Step 3: If the repeat is negative

Resume normal operations. Document the single positive, the repeat test, and the conclusion in the autoclave log. No recall of processed items is necessary if mechanical and chemical indicators were normal.

Step 4: If the repeat is positive

1. Remove the autoclave from service immediately.
2. Quarantine all instruments processed since the last negative BI. This is why the log must contain the date and load number of the last confirmed negative — it defines the recall window.
3. Recall and reprocess affected packs. If packs have already been opened and used, the infection control practitioner should assess patient risk.
4. Troubleshoot: Check for common causes — improper loading (overloading, non-sterilizable packaging), insufficient cycle time or temperature, worn door gasket, clogged chamber drain, air trapped in the chamber (failed prevacuum), or expired biological indicator. Tuttnauer's spore testing guide identifies operator error (overloading, wrong cycle, expired BI) and equipment malfunction (leaking door seal, faulty heating element) as the two main categories.
5. Retest with three consecutive fully loaded chamber cycles, all producing negative BI results, before returning the autoclave to clinical use. This requirement comes directly from CDC Table 12.
6. Document everything: dates, BI lot numbers, corrective actions, and the three negative results that cleared the unit for return to service.

Who owns the response?

Assign the failed-cycle response to a named role — typically the inventory/sterilization lead technician or the infection control practitioner designated in the AAHA ICPB Guidelines. Every staff member who runs the autoclave should know to stop using the unit and notify the designated person if a chemical indicator fails or a BI result is positive. Post the protocol next to the autoclave.

Preventive maintenance schedule

Biological indicator testing confirms sterility; preventive maintenance prevents failures. The maintenance schedule should be written, posted near the autoclave, and tracked in the same log system.

Daily

• Wipe the chamber door gasket and check for cracks or debris.
• Confirm the chamber drain is clear (a clogged drain is a common cause of wet packs and failed cycles).
• Run a visual cycle — confirm the display shows correct temperature and pressure for the selected cycle type.

Weekly

• Clean the chamber interior with an autoclave-safe cleaner (follow manufacturer instructions — avoid abrasive or chlorine-based products on stainless steel chambers).
• Run the weekly biological indicator test.
• Review the week's load log for any patterns (e.g., specific cycle types that frequently show anomalies).

Monthly

• Inspect the door gasket for wear, hardening, or cracking. Replace per manufacturer schedule or at first sign of degradation.
• Check the water reservoir (for models with integrated reservoir) and refill with distilled or deionized water only — hard water causes mineral scale that damages heating elements and clogs valves.
• Verify the chamber's safety valve is not corroded or stuck.

Annually (or per manufacturer interval)

• Schedule preventive maintenance with the manufacturer's authorized service technician. This typically includes calibration of temperature and pressure sensors, inspection of heating elements, valve function testing, and electrical safety checks.
• Document the service visit and any parts replaced in the autoclave maintenance log.

As-needed

• Descale the chamber if mineral deposits are visible (follow manufacturer procedure).
• Replace the chamber drain screen if it shows buildup.
• Replace the door gasket at the interval specified by the manufacturer or at any sign of leakage.

Building the log template

A functional autoclave log has two components:

1. Per-load log (the table described above). This can be a paper logbook kept next to the autoclave, a spreadsheet, or a digital form in the practice's quality management system. Paper is simple and inspection-friendly; digital is searchable and harder to lose.
2. BI test log (a separate section or tab). Each row records: date, autoclave ID, BI lot number, BI placement location, cycle type, incubation start time, incubation end time, result (positive/negative), control result, operator, and corrective action if applicable.

The AAHA ICPB Guidelines include a Practice Biosecurity Tracker that lists "biological indicators periodically used to ensure adequate sterilization, and results are recorded in a log" as an auditable checkbox. Design the log so that an AAHA evaluator or state inspector can locate any BI result from the past year within minutes.

Staff training and ownership

The AAHA ICPB Guidelines recommend that "all new staff [be] trained and provided with a copy of the infection control protocols" and that "periodic assessment of all staff's knowledge of related SOPs" be conducted. For the autoclave specifically:

• Onboarding. Every new technician and assistant should receive hands-on autoclave training within the first week. Cover loading technique (do not overload; place packs on their edge if possible to allow steam penetration; leave space between packs), cycle selection, chemical indicator placement, biological indicator procedure, and the failed-cycle protocol.
• Competency sign-off. After training, the new staff member runs at least three supervised cycles (including one BI test) and the trainer signs off. File the sign-off in the employee training record.
• Annual review. Review the autoclave SOP with all staff at least annually. Include a review of any failed BI events from the prior year and the corrective actions taken.

Common gaps AAHA evaluators find

The AAHA ICPB Guidelines' Practice Biosecurity Tracker lists specific autoclave-related items that evaluators check:

• Quality control sterility indicators included in each autoclaved pack
• Biological indicators periodically used to ensure adequate sterilization, and results recorded in a log
• A designated infection control practitioner overseeing the program
• Periodic assessment of staff's knowledge of and compliance with SOPs

The most common deficiencies in veterinary practice are: biological indicator testing not performed at all, testing performed but results not recorded, internal chemical indicators not used (only external strips), and no written failed-cycle protocol. All four are fixable with the log and protocol described in this article.

Sources

• AAHA Infection Control, Prevention, and Biosecurity Guidelines (2018). American Animal Hospital Association. https://www.aaha.org/wp-content/uploads/globalassets/02-guidelines/infection-control/icpb_guidelines.pdf
• CDC Guidelines for Disinfection and Sterilization in Healthcare Facilities — Table 12: Suggested protocol for management of positive biological indicator in a steam sterilizer. Centers for Disease Control and Prevention. https://www.cdc.gov/infection-control/hcp/disinfection-and-sterilization/management-positive-indicator.html
• CDC Best Practices for Sterilization Monitoring — Biological monitoring. Centers for Disease Control and Prevention. https://www.cdc.gov/dental-infection-control/hcp/dental-ipc-faqs/sterilization-monitoring.html
• CDC Guidelines for Disinfection and Sterilization — Sterilizing Practices. Centers for Disease Control and Prevention. https://www.cdc.gov/infection-control/hcp/disinfection-and-sterilization/sterilizing-practices.html
• Tuttnauer. Spore Testing for Your Autoclave: Why, How and When. https://tuttnauer.com/blog/spore-testing-your-autoclave-why-how-and-when
• Woodhouse Laboratories. Chemical vs Biological Indicators — Why Do I Need Both. https://www.woodhouselabs.com/chemical-vs-biological-indicators-why-do-i-need-both
• FAU Comparative Medicine SOP #111.4: Processing Biological Indicators. Florida Atlantic University. https://www.fau.edu/research-admin/comparative-medicine/documents/cm-sop-111.4-processing-of-biological-indicators-ada.pdf
• Consolidated Sterilizer Systems. Autoclave Log Sheet Template and Tracking Guide. https://consteril.com/autoclave-log-sheet-template
• AAHA Practice Biosecurity Tracker (accompanying the 2018 ICPB Guidelines). https://www.aaha.org/resources/2018-aaha-infection-control-prevention-and-biosecurity-guidelines/practice-biosecurity-tracker