Understanding Medical Device Reprocessing - Part 3, sterilizing

Sterilizing medical instruments is a critical step in preventing infections and ensuring patient safety. After instruments are inspected, lubricated, packaged, and processed, sterilization completes the cycle by eliminating all micro-organisms, including spores. This post explores the sterilization process, focusing on autoclave use and spore testing to verify effectiveness.

Preparing Instruments for Sterilization

Before sterilization, instruments must be carefully inspected and maintained. Inspection helps identify damage or wear that could compromise sterilization or patient safety. Instruments are examined under magnification to ensure no debris has been missed during the cleaning process, that all joints line up properly, and that instruments are in good working order. A medical lubricant that is compatible with the instruments and the autoclave is used for hinged instruments to prevent corrosion and ensure smooth operation.

Packaging protects instruments from contamination after sterilization and during storage. Instruments are packaged in paper/plastic pouches that allow steam to penetrate, but keep out pathogens after processing. These packages have Class 4 chemical indicators on them that change colour when the package has been subjected to 2 or more of the required parameters: time, temperature, and/or steam. So long as these packages remain dry and intact, the contents are considered sterile indefinitely.

Canadian standards for foot care instruments require a Class 5 chemical indicator to be added to the package. It has a "moving front" that travels from "reject" to "accept" as all three of the required parameters are met. If a package goes through the sterilization process but the indicator does not make it into the "accept" field, the instruments must be repackaged and put through the sterilizer again.

Proper preparation ensures sterilization is effective and instruments remain safe for use.

Using the Autoclave for Sterilization

The autoclave is the most widely used sterilizer in healthcare settings. It uses pressurized steam at high temperatures to kill all micro-organisms, including bacterial spores, which are among the most resistant forms of life.

The Vacuum Autoclave

Autoclaves operate by exposing instruments to steam at temperatures typically between 121°C (250°F) and 134°C (273°F) for a specific time, depending on the cycle. The combination of heat, moisture, and pressure destroys micro-organisms by denaturing proteins and disrupting cell membranes.

A vacuum autoclave (or prevacuum sterilizer) works by using a vacuum pump to mechanically remove all air from the chamber and load, replacing it with high-pressure, high-temperature steam (132-135°C). This process uses alternating vacuum and pressure pulses to ensure steam penetrates porous materials (fabrics) or hollow instruments. The Canadian Standards Association requires the use of a vacuum autoclave for the processing of foot care instruments. This is the same type of autoclave required in hospitals to sterilize surgical instruments.

Sole Focus has a small table-top model, from Enbio. It holds a smaller load than a traditional table-top autoclave, but it has a significantly shorter cycle time, and takes up much less space. It is also easier to maintain, as regular testing and maintenance is required to ensure an autoclave is working properly. A typical work week generates enough instruments for 3-5 loads.

Traditional table-top sterilizer

Enbio table-top sterilizer

Verifying Sterilization with Spore Tests

Sterilization must be verified regularly to confirm that the process effectively kills all micro-organisms. Spore tests provide the most reliable method for this verification.

Spore tests use highly resistant bacterial spores, such as Geobacillus stearothermophilus, placed inside test strips in vials containing a growth medium. These spores are not harmful to humans. They survive most cleaning processes but are killed by proper sterilization.

After running the autoclave cycle, the test strips are incubated at 60°C for 10-24 hours, depending on the test type. If spores grow, it indicates sterilization failure. Any loads processed since the last time a spore test passed must be pulled from use, repackaged, and resterilized.

No growth confirms the cycle was effective. Only after the spore test is complete are instruments released to be used. Spore tests are performed at a minimum with the first load of the week, and after any maintenance or repair. The results of the test load are recorded in a log book that can be requested at any time by the BC College of Nurses & Midwives, or an Environmental Health Officer.

After incubation, there should be no change in the colour of the contents. An unsterilized vial is incubated as a control.

After going through the autoclave, the chemical indicator on the spore vial should have changed colour.

Summary

Sterilizing medical instruments is a complex but essential process. Foot care professionals must follow protocols closely and perform regular testing to ensure instruments are safe for use. Following these steps supports infection control and improves outcomes in foot care.