At the spring 2019 IAHCSMM Annual Conference & Expo in Anaheim, CA, Beyond Clean hosted a discussion of sterilization process monitoring with chemical indicators, biological indicators, and by parametric release. The first two items are quite familiar to U.S. SPD personnel, being part of everyday life and whose use is defined in AAMI ST79:2017. On the other hand, parametric release is not typically done in U.S. SPDs and, because it doesn’t use integrators or biological indicators, it may seem like an act of faith where no faith is warranted. But its principles can provide a better understanding of the function of your sterilizers (and washers) and help you set up programs to maintain their optimal function. This article is being provided to help you understand what parametric release is, what is needed to do it, and which of its principles can be applied to improve your daily processing.

[To view a roundtable discussion about parametric release, biological indicators, and chemical indicators, watch the Myth Busting 2019 Sterility Assurance Debate hosted by Beyond Clean at IAHCSMM 2019. Take the quiz for CE credit.—Ed.]


CE credit:

Parametric release: What is it?

By its name, parametric release implies that products are released to the healthcare institution for patient use based upon monitoring the parameters of the washing and sterilization processes. There are no indicators, except Type 1 on the labels, locks, or pouches. None. Period.

In reality, anything that is too good to be true is too good to be true. You have to close the process control loop and verify, or even validate, that the load will be sterile.

Parametric release, where it is done in healthcare facilities, typically is applied to steam sterilization more than any other process. This is because steam sterilization is the easiest process for performance verification based upon process parameters: temperature, pressure, and cycle running according to the programming of the unit. End of story, right? No.

Successful sterilization requires that the prescribed sterilization conditions be met throughout the load. This is why you scatter integrators like confetti (well, almost) throughout the interior of challenging trays to make sure that the integrators all show successful sterilization conditions were present throughout the tray. If you use integrators to do this normally, and you don’t use them in parametric release, then how do you do this with parametric release?

Let’s take a little stroll into the process of validating a sterilizer for parametric release. First, you have to go through a complete installation qualification (IQ) and operational qualification (OQ).[1] Installation qualification is the process of obtaining and documenting evidence that equipment has been provided and installed in accordance with its specification. In other words, the machine is what you ordered, the utilities are correct, you plugged it in, and it didn’t blow a fuse or leak compressed air (if any) or water.

Operational qualification is the process of obtaining and documenting evidence that installed equipment operates within predetermined limits when used in accordance with its operational procedures. In other words, it passed IQ, was calibrated (either during IQ or OQ), and runs the cycles you expect it to within specification.

Finally, you do a performance qualification (PQ), which is what enables parametric release. Performance qualification, defined in the cited ISO document as the process of obtaining and documenting evidence that the equipment, as installed and operated in accordance with operational procedures, consistently performs in accordance with predetermined criteria and thereby yields product meeting specifications. In the case of sterilizers, this means that sterilization conditions are established throughout the load. But which load? A load that you define either as a worst-case challenge for the process compared to all other loads, or as a master product for a product family. See AAMI ST79:2017, definition 2.66, section 13.9.1.

Almost no one in the U.S. healthcare world qualifies their processing equipment in a properly documented manner. You can’t do parametric release if you don’t do this, so what do you have to do? The following is based upon sterilization. Application of validation to washers, ultrasonics, and automated endoscope reprocessors (AERs) is similar, but requires specific aspects of those machine types to be tested.

  1. Carry out an IQ:
    • Make sure it’s the machine you ordered, and that all utilities meet the requirements stated by the manufacturer.
  2. Its documentation must represent the as-built state of the machine, so you have to check everything.
    • Calibrate the temperature and pressure transducers and timers to a standard traceable to an American national primary standard.
    • Carry out steam quality measurements to demonstrate compliance with the manufacturer’s requirements, or those of AAMI ST79:2017, section
    • Verify that all utilities are within the manufacturer’s prescribed limits. This means electricity, fusing and circuit breakers, water quality, water pressure, and steam pressure.
  3. Carry out an OQ:
    • Make sure it runs the cycles per specification.
    • Test all error responses.
    • Make sure it passes a vacuum leak test.
    • Make sure it passes three consecutive Bowie-Dick tests.
    • Map the temperature of the empty chamber in a cycle in at least five places, preferably 10, with one being the drain.
  4. Carry out a PQ:
    • Use the master product as your test load. You should respect the requirements of AAMI ST79, section 13.8.
    • Map temperatures within the master product. They all must reach the sterilization conditions (temperature between setpoint –0 and +6°F) for the stated duration of the exposure phase, typically 4:00 minutes.
    • Place biological indicators with at least a 105 population of stearothermophilus spores (the same indicators you use now) adjacent to the temperature sensors in the load. All biological indicators (BIs) must be inactivated by the cycle.
    • Do this for a small load (one master product) and a full load (fill the chamber with master products), three cycles each for each load configuration. This is similar to container evaluation testing in AAMI ST79:2017, section
    • If possible, this should be done in half the exposure time, since your cycle is supposed to provide overkill such that there is a one-in-a-million chance of an unsterile item. Doubling the exposure time that kills all BIs provides this safety margin, also known as sterility assurance level (SAL).
    • If all the BIs are killed, you have successfully done a performance qualification.

The full load test sets out your worst-case load and sets the performance bar for releasing loads that are as challenging or less challenging than the master product loads. Easy peasy. Not really.

You have to do a full requalification following the same procedure every year, or after a major repair. No more three test packs or three Bowie-Dicks. This is serious business, as are your patients’ lives.

How does this break down for the SPD?

  1. You don’t own temperature profiling equipment.
  2. You don’t normally calibrate pressure and temperature sensors.
  3. You don’t get into the electrical and plumbing systems of the sterilizer to test wiring and plumbing and compliance of drawings to prove that the sterilizer is built per plan.
  4. Parametric release usually involves double-door, pass-through sterilizers so that items that are not sterile do not ever get to the clean side.
  5. You don’t do this for a living. You are there to make the instruments come out clean and sterile, so this is unknown territory and not for the untutored.

What can you learn from this and how can you use these tools to make your SPD run better? Here are a few things you can do to ensure product and process excellence.

From IQ:

  • Have the utilities monitored or checked periodically (quarterly, twice a year, annually at worst).
  • Do steam quality testing to make sure that your steam meets the requirements of AAMI ST79:2017, section If these requirements are met, wet packs can become never events, and you can decrease your dry time to what the device manufacturers recommend (maybe—it depends a lot on the drying phase).
  • Calibrate the transducers instead of relying on BIs and chemical indicators (CIs) to tell you if things have gone horribly wrong in your process control. The sterilizer will always tell you that it is in control of the process until it is unable to run the cycle. The sterilizer doesn’t know if the calibration has drifted.

From OQ:

  • Do vacuum leak tests periodically. Watch for trends toward worse results.
  • Do periodic qualification with Bowie-Dick tests.

From PQ:

  • Do master product testing with worst-case loads. Use Type 6 chemical indicators instead of BIs and temperature datalogging to show that the sterilization conditions were met at the locations tested. Type 6 indicators are recommended because they are supposed to last longer in the cycle than BIs or Type 5 CIs, providing a worst-case challenge. Biological indicators and Type 5 indicators can also be used for traceability to traditional measures.

What do you gain by this?

  • Assurance that your sterility assurance is real and not a matter of prayer. More efficient processing.
  • Insight into the equipment to know that it is behaving, or that it is heading toward a problem.
  • A measure of your margin of safety that the process actually provides, not what it is supposed to be.

The investment is not huge in time and money. Productivity increases and decreased failure rates can pay for that investment in very little time.


  1. ISO TS 11139:2018, “Sterilization of health care products – Vocabulary of terms used in sterilization and related equipment and process standards,” International Organization for Standardization, Geneva, 2018.