CMDRT - Certified Medical Device Reprocessing Technician Steam Sterilization Principles Questions and Answers 2 — Questions and Answers
Question 1: What are the three critical parameters that must be achieved for effective steam sterilization?
- Pressure, colour, and smell
- Time, temperature, and steam quality (saturated steam with direct contact) (Correct answer)
- Weight, volume, and density
- Speed, pressure, and dryness
Correct answer: Time, temperature, and steam quality (saturated steam with direct contact)
Steam sterilization requires saturated steam at the correct temperature (121°C or 132°C) maintained for the required exposure time with direct steam contact on all surfaces. All three parameters must be met simultaneously.
The three critical parameters of steam sterilization, as defined by CSA Z314.3, are interdependent: (1) Temperature — saturated steam must reach and maintain the required temperature throughout the chamber and within all packages. Standard parameters are 121°C (gravity displacement cycles) or 132-134°C (dynamic air removal/prevacuum cycles). (2) Time — the exposure time begins only after the chamber reaches the target temperature and must be maintained for the specified duration (e.g., 30 minutes at 121°C for gravity, or 4 minutes at 132°C for prevacuum). (3) Steam quality — the steam must be saturated (containing maximum moisture at its temperature/pressure) and must make direct contact with all surfaces of all items. Superheated steam (too dry) is less effective because it behaves like hot air, lacking the latent heat energy release that occurs when saturated steam condenses on cooler surfaces. The relationship between temperature and pressure is fixed by the physics of steam — pressure is not an independent variable but rather a consequence of achieving the target temperature.
Question 2: What is the difference between a gravity displacement sterilizer and a prevacuum sterilizer?
- They are identical machines with different names
- A gravity displacement sterilizer relies on steam displacing air downward by gravity, while a prevacuum sterilizer uses a vacuum pump to actively remove air before steam admission (Correct answer)
- Gravity sterilizers are faster than prevacuum sterilizers
- Prevacuum sterilizers do not use steam
Correct answer: A gravity displacement sterilizer relies on steam displacing air downward by gravity, while a prevacuum sterilizer uses a vacuum pump to actively remove air before steam admission
In gravity displacement, steam enters the top of the chamber and pushes air out through a drain at the bottom. Prevacuum sterilizers actively pull air out using a vacuum pump before introducing steam, resulting in faster and more complete steam penetration.
The two main types of steam sterilizers differ fundamentally in their air removal method, which significantly impacts performance. Gravity displacement sterilizers rely on the physical principle that steam (being lighter than air) enters the top of the chamber and pushes cooler, heavier air downward and out through a drain/vent at the bottom. This is a slower, passive process, and air pockets can remain trapped in complex loads, porous materials, and within lumened devices. Typical gravity cycles require longer exposure times (e.g., 30 minutes at 121°C or 10 minutes at 132°C). Prevacuum (dynamic air removal) sterilizers use a vacuum pump to actively extract air from the chamber through a series of vacuum and steam pulses (conditioning phase) before the exposure phase begins. This active air removal is faster and more thorough, enabling shorter cycle times (e.g., 4 minutes at 132°C) and better penetration into porous materials and complex loads. CSA Z314.3 requires daily Bowie-Dick testing of prevacuum sterilizers to verify adequate air removal.
Question 3: What is the Bowie-Dick test and why is it performed daily?
- A test of the sterilizer's door seal
- A specific test for prevacuum sterilizers that verifies adequate air removal from the chamber, performed daily before the first patient load (Correct answer)
- A biological indicator test
- A test performed only during annual maintenance
Correct answer: A specific test for prevacuum sterilizers that verifies adequate air removal from the chamber, performed daily before the first patient load
The Bowie-Dick test uses a standardized test pack to detect air leaks and inadequate air removal in prevacuum sterilizers. Trapped air prevents steam contact with instrument surfaces and can result in sterilization failure.
The Bowie-Dick test (also called the air removal test or Type 2 chemical indicator test) is a critical daily quality assurance test for prevacuum steam sterilizers. The test uses a standardized test pack (commercially available or facility-prepared) containing a Type 2 chemical indicator sheet placed in the centre. The test pack is run in an otherwise empty chamber using a standard prevacuum cycle. If the vacuum system is functioning correctly and removing air adequately, the chemical indicator will show a uniform colour change across the entire sheet. If air removal is inadequate (due to a vacuum pump malfunction, air leak, or insufficient conditioning pulses), residual air will prevent steam from penetrating to the centre of the test pack, resulting in a lighter or incomplete colour change. CSA Z314.3 requires the Bowie-Dick test to be run daily as the first cycle before any patient loads are processed. A failed Bowie-Dick test means the sterilizer must be taken out of service until the problem is identified and corrected.
Question 4: Why is the drying phase important in steam sterilization?
- Drying makes instruments shine
- Adequate drying prevents wet packs, which compromise the sterile barrier by allowing microbial migration through moisture on the packaging (Correct answer)
- Drying is optional and can be skipped to save time
- The drying phase sterilizes the outside of packages
Correct answer: Adequate drying prevents wet packs, which compromise the sterile barrier by allowing microbial migration through moisture on the packaging
Residual moisture on sterilized packages (wet packs) creates a pathway for microorganisms to wick through the packaging material, compromising sterility. The drying phase uses vacuum and heat to remove condensate.
The drying phase at the end of a steam sterilization cycle is critical for maintaining the sterile barrier of processed packages. During the exposure phase, steam condenses on cooler surfaces (instruments, packaging) to deliver its latent heat energy for microbial killing. This condensation must be removed before packages are considered sterilized and ready for storage. If packages remain wet (a condition known as 'wet packs'), the moisture creates a pathway for microorganisms to migrate through the packaging material via capillary action (wicking), compromising sterility. CSA Z314.3 states that any package that is wet or has visible moisture after the sterilization cycle must be considered non-sterile and must be reprocessed. The drying phase typically uses vacuum to lower the boiling point of residual water and continued chamber heat to evaporate moisture. Factors contributing to wet packs include overloading the sterilizer, inadequate drying time, improper loading (packages touching chamber walls), poor steam quality, and cold instruments.
Question 5: What is a biological indicator (BI) and how is it used in steam sterilization monitoring?
- A colour-changing tape on the outside of packages
- A preparation of highly resistant bacterial spores (Geobacillus stearothermophilus) used to directly challenge the sterilization process and confirm microbial kill (Correct answer)
- A pH test of the steam
- A temperature recording device
Correct answer: A preparation of highly resistant bacterial spores (Geobacillus stearothermophilus) used to directly challenge the sterilization process and confirm microbial kill
Biological indicators contain a known population of Geobacillus stearothermophilus spores, which are among the most resistant microorganisms to moist heat. A negative BI result (no growth after incubation) confirms the sterilization process was lethal.
Biological indicators (BIs) are the gold standard for monitoring steam sterilization effectiveness because they directly measure the process's ability to kill highly resistant microorganisms. For steam sterilization, BIs contain spores of Geobacillus stearothermophilus (ATCC 7953), selected because these spores are among the most resistant organisms to moist heat sterilization. A BI typically consists of a paper strip or self-contained vial inoculated with a defined population of spores (usually 10^5 to 10^6). The BI is placed in the most challenging location within the sterilization load (typically the centre of the densest package or the geometric centre of the load), processed through a normal cycle, and then incubated at 55-60°C for the manufacturer's recommended time (24-48 hours for conventional BIs, or as little as 1-3 hours for rapid-readout BIs). No growth (negative result) indicates the sterilization process was effective. A positive result (growth detected) indicates a sterilization failure. CSA Z314.3 requires BIs at minimum daily, with every implant load, and after sterilizer installation, repair, or relocation.
Question 6: What is the concept of sterility assurance level (SAL) and what SAL is required for medical devices?
- SAL measures the weight of a sterile package
- SAL of 10^-6 is required, meaning the probability of a viable microorganism surviving the sterilization process is no more than one in one million (Correct answer)
- Any SAL above 50% is acceptable
- SAL is only relevant for pharmaceutical products
Correct answer: SAL of 10^-6 is required, meaning the probability of a viable microorganism surviving the sterilization process is no more than one in one million
A SAL of 10^-6 is the internationally accepted standard for medical device sterilization, meaning that after a properly validated sterilization cycle, the probability of any given device being non-sterile is less than one in a million.
The Sterility Assurance Level (SAL) is a statistical concept that defines the probability of a viable microorganism being present on a device after sterilization. For medical devices, the internationally accepted SAL is 10^-6 (one in one million), as specified by CSA Z314.3, ISO 17665 (steam sterilization), and other sterilization standards. This means that for every one million devices sterilized, the probability of one device being non-sterile should be no greater than one. Achieving this SAL depends on several factors: (1) Bioburden — the number and type of microorganisms on the device before sterilization (which is why thorough cleaning is essential). (2) Sterilization cycle parameters — validated time, temperature, and steam quality that provide a significant overkill margin. (3) D-value — the time required at a given temperature to reduce the microbial population by 90% (one log). Standard steam sterilization cycles are designed with a substantial overkill margin, providing exposure far beyond what is needed to achieve a 10^-6 SAL from normal bioburden levels.
CMDRT - Certified Medical Device Reprocessing Technician Steam Sterilization Principles Questions and Answers 2
What are the three critical parameters that must be achieved for effective steam sterilization?