Transcript Variation-in-Sterilization

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
Background: Biological Indicators,
Class 5 and Class 6 Indicators.
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 vs. Class 6 Indicators
Class 5 integrators are
intended to mirror the death
curve 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.
Background: Biological Indicators,
Class 5 and 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.
Background: Biological Indicators,
Class 5 and Class 6 Indicators.
A Class 6 indicator provides
a much more significant test to
sterilizer efficacy than a Class 5
INDICATOR
134°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
Typical sterilizer cycle vs. Indicator
validation conditions.
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
ANSI / AAMI / ISO 11140-4 B-1 CYCLE
ANSI / AAMI / ISO 11140-4 B-2 CYCLE
Typical sterilizer cycle vs. Indicator
validation conditions.
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.).
Real World Examples: Sterilizer Malfunction
Real World Examples: Sterilizer Malfunction
•10 inHg vacuum
(approx 300
millibars)
•Normal setting is 28
inHg (approx 7o
millibars)
Real World Examples: Sterilizer Settings
Real World Examples: Sterilizer Settings
Time
Temp in °C
Pressure in
millibars
08:36:08
76.0
1765
08:38:05
71.5
70
08:38:19
96.7
1200
08:39:14
71.3
70
08:39:33
106.0
1350
08:40:22
64.2
70
08:40:45
109.8
1500
Real World Examples: Sterilizer Settings
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
1765
08:38:05
71.5
70
08:38:19
96.7
1200
08:39:14
71.3
70
08:39:33
106.0
1350
08:40:22
64.2
70
08:40:45
109.8
1500
Real World Examples: Sterilizer Settings
Real World Examples: Sterilizer Settings
Pass result indicated
by machine, fail
result indicated by
indicator.
Real World Examples: Sterilizer Settings
Real World Examples: Sterilizer Settings
Machine
indicates
“Pass”
Vacuum level
of 60kpa
Real World Examples: Sterilizer Settings
•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.
Vacuum level
of 60kpa
Real World Examples: Sterilizer Idiosyncrasies
INCONSISTENT STERILIZER PERFORMANCE DUE TO FLUCTUATIONS IN IDLE TIME
•
•
•
•
Exposure Time
Idle Time
Temp in °C
BI Survival Rate
4 minutes
75 minutes
132
97%
4 minutes
15 minutes
132
50%
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.
Lessons
 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.