Lumen claims of the STERRAD 100NX
Sterilizer: Testing performance limits of
this technology
Magda Diab-Elschahawi, Alexander Blacky, Walter Koller
Clinical Institute of Hospital Hygiene
Medical University of Vienna
STERRAD100NX™ Sterilizer
STERRAD 100NX Full Cycles
• Standard Cycle – 47 minutes
Sterilization of most surgical instruments including Inox
lumened devices
AND
• Flex Cycle – 42 minutes
Sterilization of flexible endoscopes only
Study Background
• A main drawback in the past has been the reliable sterilization of devices featuring long narrow lumens.
• According to the manufacturers information the STERRAD100NX™ Sterilizer can adequately process 0.7mm X 500mm Inox lumened devices.
• We placed inoculated carriers at the midpoint position of lumens, which were then submitted to half-cyclesterilizing conditions in the STERRAD100NX™ Sterilizer.
• In order to simulate insufficient cleaning of instruments or crystalline residues we added organic and inorganic challenges respectively to our inoculated carriers.
Aim of the study
• The aim of this study was to qualify the performance of the STERRAD100NX™ Sterilizer under different experimental settings* representing worst case conditions.
• Protocol:
1. Stainless steel lumens of 0.7mm x 500mm
2. Wrapping (1 X)
3. Flex Scope conditions
4. Organic and inorganic burdens
* These conditions do not correspond to the manufacturer’s instructions for use
Test Conditions
Manufacturer’s IFU University Worst Case
Test Condition
Lumen Claim 0.7 mm X 500 mm Inox 0.7 mm X 500 mm Inox*
Instrument Condition Must be clean and dry Contaminated with
inorganic and organic
material
Load Arrangement Arranged pouches on
edge
Pouches stacked on top
of each other
Sterilization Cycle STANDARD FLEX
* 0.7 mm X 500 mm Inox are validated for sterilization only in the
STERRAD 100NX STANDARD cycle. Do not process these
devices in the FLEX cycle.
Rationale for Worst Case
Conditions
• Cleaning process not validated >> sub-standard washing or rinsing– Simulated by use of inorganic and organic soils
• Human Error >>Improper loading– Simulated by stacking pouched lumens on top of each
other
• Human Error >> selecting the wrong cycle for the devices to be processed– Simulated by use of FLEX cycle for sterilization of a
rigid lumen
Test load
Test load upper shelf Test load lower shelf
Manfacturer’s Recommendation
Place pouches on edge
Experimental setting
BI (condition) Mean spore count/ml SD Final titer (mean)
unchallenged 5,08E+00 ± 2,81 5,08E+05
300ppm 1,23E+01 ± 4,01 1,23E+06
600ppm 1,77E+01 ± 4,63 1,77E+06
1200ppm 1,37E+01 ± 2,77 1,37E+06
5%FBS 1,88E+01 ± 4,07 1,88E+06
Titer verification
condition position number 1 2 3 4 5 6 7 8 9 10
untreated cycle 2 nG G nG nG G G nG nG nG nG
cycle 3 nG G nG nG nG nG nG G nG nG
cycle 4 nG G nG nG nG nG nG nG nG nG
negative (%) 100% 0% 100% 100% 66% 66% 100% 66% 100% 100%
300ppm cycle 2 G G G G G G G G G G
cycle 3 G G G G G G G G G G
cycle 4 G G G G G G G G G G
negative (%) 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%
600ppm cycle 2 G nG nG G nG nG G G nG nG
cycle 3 G G G G G G G G G G
cycle 4 G G G G G G G G G G
negative (%) 0% 33% 33% 0% 33% 33% 0% 0% 33% 33%
1200ppm cycle 2 G G G G G G nG G G G
cycle 3 G G G G G G G G G G
cycle 4 G G G G G G G G G G
negative (%) 0% 0% 0% 0% 0% 0% 33% 0% 0% 0%
5% FBS cycle 2 G G G G G G G G G G
cycle 3 G G nG G nG G G G G G
cycle 4 nG G G nG G G G G G G
negative (%) 33% 0% 33% 33% 33% 0% 0% 0% 0% 0%
Qualitative Results
Quanitative results
wires
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
1 2 3 4 5 6 7 8 9 10
position numbers
log
redu
ctio
n/w
ire
untreated
300ppm
600ppm
1200ppm
5%FBS
Besides the protocol:
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
1 2 3 4 5 6 7 8 9 10
log
re
du
cti
on
/BI
position numbers
untreated
untreated HS
Untreated wires: Heatshock vs. non Heatshock
Discussion
• The titer determination of the inoculated wires in unchallenged condition provided by ASP showed a titer of only 5.08 x 105.
• As our quantitative results showed that CFU counts of unchallenged wires found after sterilization were below detection limit, the actual log reduction rate can only be stated as ≥ 5.71.
• Though one can assume, that a SAL of 10-6 could be achieved, a positive verification would have required a higher inoculation of the BI’s.
• We also cannot rule out that an effect known as
inoculum effect would not influence the test results had
we had a higher initial test inoculum.
• The inoculum effect refers to a decrease of the effect of
a microbicide associated with a higher inoculum as
described for antibiotics and certain disinfectants.
• The increase in bio-burden going along with an
increasing inoculum size would decrease the amount of
available sterilant per bacterial cell. Hence in our case
H2O2 might fail to kill all test-organisms, thus resulting in
inadequate sterilization especially in situations with
heavy contamination and insufficient previous cleaning.
Discussion
• Inoculum effects must be considered relevant in all
situations where biocides are not abundant in relation to
microbial inocula.
Discussion
Recommendations regarding the
STERRAD100NX™
• strictly adhere to the manufacturer’s
recommendations specified in their user guide
• correct cycle (Standard or Flex Scope) and
• permitted dimensions for the processing of
medical devices with lumens in the STERRAD
100NX Sterilizer.
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Thank you for your attention!