Variation in Sterilization Cycles : The continued need for load monitoring devices

Variation in Sterilization Cycles: The continued need for load monitoring devices.

OVERVIEW• BACKGROUND: BIOLOGICAL INDICATORS, CLASS

5 INDICATORS AND CLASS 6 INDICATORS DEFINED• A TYPICAL STERILIZER CYCLE AND HOW THIS

DIFFERS FROM INDICATOR VALIDATION CONDITIONS

• REAL WORLD EXAMPLES AND THE NEED FOR LOAD MONITORING: (1) STERILIZER MALFUNCTION, (2) STERILIZER SETTINGS AND (3) STERILIZER IDIOSYNCRACIES

The question we’re hearing more and more frequently:

If my indicator passed a minute or two into the exposure phase ----

THEN WHAT GOOD IS IT?

Background: Biological Indicators, Class 5 and Class 6 Indicators.

Class 5 integrators are intended to mirror the deathcurve of the Geobaccilus Stearothermophilus bacteria with a margin of safety.

Note that this statement is only true with respect to naked BI strips. There is no correlation between a Class 5 and a self contained biological indicator.

Class 5 vs. Class 6 Indicators


Class 6 emulators vs. Class 5 integrators. At a given cycle point, a Class 6 emulator provides significantly more resistance to the sterilization process than a Class 5 integrator and thus is a more effective load monitoring device.

ISO 11140-1 standard for Class 6 is that the indicator must pass at the stated value and must fail at -1°C and -6% time.

ISO 11140-1 standard for Class 5 is that the indicator must pass at the stated value and must fail at stated value temperature and 63.6% of stated value time.

Typically the stated value for a Class 5 at 134°C is approx. 2 minutes. The stated value for a Class 6 at 134°C is 3.5, 4 minutes or longer depending on the cycle in question.

At 134°C, a Class 6 has at least twice the stated value and has a 2.5 times tighter tolerance.

vs.


A Class 6 indicator provides a much more significant test to sterilizer efficacy than a Class 5

INDICATOR134°C

4 MINUTES

133°C 3.76

MINUTES

134°C 3.5

MINUTES

133°C 3.29

MINUTES

CLASS 6 PASS FAIL PASS FAIL

CLASS 5 PASS PASS PASS PASS


PER ISO 11140-1 (STANDARD GOVERNING INDICATOR PERFORMANCE) CHEMICAL INDICATORS ARE VALIDATED IN BIER (BIOLOGICAL INDICATOR EVALUATION RESISTOMER) VESSELS. EXPOSURE CONDITIONS IN BIER VESSEL DIFFER GREATLY FROM THOSE IN STERILIZER: One pre-vacuum pulse is pulled. Phase cannot exceed 2

minutes. Exposure temp is achieved in less than 10 seconds One exhaust vacuum is pulled. Phase cannot exceed 1

minute. Temperature tolerance of +/- 0.5°C

Typical sterilizer cycle vs. Indicator validation conditions.

ANSI / AAMI / ISO 11140-4 B-1 CYCLE

ANSI / AAMI / ISO 11140-4 B-2 CYCLE

MOST STERILIZER CYCLES ARE A HYBRID OF THE B-1 AND B-2 CYCLES, WHERE A DEEP VACUUM (E.G. 70 MILLIBARS) IS PULLED BUT THERE ARE ALSO SIGNIFICANT POSITIVE PRESSURE PULSES (E.G. 1500-2000 MILLIBARS) ALTERNATING WITH EACH VACUUM PULSE. Multiple vacuum pulses. Total duration of 15-20 minutes, with temps

oscillating between 100°C-130°C (compared to one short pre-vac pulse). Exposure temp is achieved in as much as 5-7 minutes after last vacuum

pulse (compared to less than 10 seconds). One exhaust vacuum is pulled, with dry phase lasting 20-30 minutes

(compared to 1 minute or less). Exposure temp often exceeds setting by 1.5°C + (compared to

temperature tolerance of +/- 0.5 C). While the pre-vac phase might do a lot of the heavy lifting towards

changing an indicator, a passed indicator means that adequate conditions were achieved wherever the indicator was placed (in a pouch, tray, pack, PCD etc.).

Typical sterilizer cycle vs. Indicator validation conditions.

Real World Examples: Sterilizer Malfunction

•10 inHg vacuum (approx 300 millibars) •Normal setting is 28 inHg (approx 7o millibars)

Real World Examples: Sterilizer Malfunction

Real World Examples: Sterilizer Settings

Time Temp in °C Pressure in millibars

08:36:08 76.0 176508:38:05 71.5 7008:38:19 96.7 120008:39:14 71.3 7008:39:33 106.0 135008:40:22 64.2 7008:40:45 109.8 1500


What went wrong?• Come up time is way too fast.• ISO 11140-4 sets upper limit

for come up time at 250kpa/min or 42mbar/second.

• This sterilizer had a come up time of 67mbar/second or 60% over the upper limit established by the norm.

• Most sterilizer manufacturers set their come up time to around 10mbar/sec to ensure adequate air removal and lethality.

Time Temp in C

Pressure in millibars

08:36:08 76.0 176508:38:05 71.5 7008:38:19 96.7 120008:39:14 71.3 7008:39:33 106.0 135008:40:22 64.2 7008:40:45 109.8 1500



Pass result indicated by machine, fail result indicated by indicator.



Vacuum level of 60kpa

Machine indicates “Pass”


Vacuum level of 60kpa

•60 kpa (or approx 600 millibars)

• ISO 11140-4 calls for an initial pulse to 5kpa and then additional pulses with at least a 50kpa vacuum depth, depending on cycle (sub-atmospheric, trans-atmospheric or super-atmospheric).

•When we validated for the ISO 11140-4 norm, we set the fail cycle at 250 millibars deeper than the setting on this machine.

•Inadequate vacuum can result in residual air inside of pouches, packs and trays.


• We have seen about a 40% drop in efficiency in sterilizers that idle for more than 60 minutes.

• True across sterilizer brands. Our test was conducted on a major brand, a customer validated on another major brand.

• Harborview Med Ctr (Univ of Washington Medicine): “I … ran three tests side by side, one that had been idle for 30 min one that was idle for 60 min and one that wasn't idle at all and I found that all three tests with the 60 min idle had positive BIs. So it was logical to conclude that there was a drop off in efficiency that had to be corrected for prior to using the devices for loads.”

• These results make sense and don’t mean that the sterilizers are malfunctioning. On the first cycle after extended idle time, energy is expended heating sterilizer chamber walls, which has a deleterious effect on sterilizer efficiency.

Exposure Time

Idle Time Temp in °C BI Survival Rate

4 minutes 75 minutes 132 97%4 minutes 15 minutes 132 50%

Real World Examples: Sterilizer Idiosyncrasies

INCONSISTENT STERILIZER PERFORMANCE DUE TO FLUCTUATIONS IN IDLE TIME

Sterilizer exposure conditions differ greatly from validation conditions inside of a BIER vessel. While the pre-vac phase might do a lot of the heavy lifting towards changing an indicator, a passed indicator means that adequate conditions were achieved wherever the indicator was placed (in a pouch, tray, pack, PCD etc.).

At a given cycle point, a Class 6 indicator is significantly more resistant than a Class 5 indicator.

There is wide variation in sterilizer performance, due to a number of potential factors: (1) malfunction, (2) settings or (3) idiosyncrasies. Occurrences falling under categories (2) and (3) in some ways pose the greatest risks because, on the surface, everything seems to be working, and these cannot be detected by calibrations / preventive maintenance.

Load monitoring devices are validated to norms. A good load monitoring device should act as a constant amidst the many variables that are involved in sterilization by enabling the CSSD professional to compare sterilizer performance to the baseline performance established by the applicable norm.

Lessons

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Variation in Sterilization Cycles : The continued need for load monitoring devices