Can Hydrogen Peroxide Sterilization Chemical Indicators be used to estimate the sterilant

dose delivered to instrument sets?

Preliminary Findings

Name:Dr Brian Kirk

Affiliation:Brian Kirk Sterilization Consultancy Group Ltd UK

17 / 20 NOVEMBER 2021CICG, GENEVA, SWITZERLAND

Contents

2

Basics of VH2O2 sterilization

What needs to be Monitored

How can we monitor

Conventional vs Dosimetry

What is Dosimetry

Dosimetry in Irradiation, Moist Heat, VH2O2 sterilization

Chemical Indicators as Dosimeters

Calibration of visual response vs exposure dose (mg.s/L) for 8 CIs

Estimation of dose using CIs

Model Loads

Response of the CIs.

Conclusions

Sterilization Processes used for Medical Devices Sterilization

Processes

Physical Chemical

Mechanical Removal(Filtration)

Hot Cold

Moist Heat(Steam)

Dry Heat

UV Light

Ionising radiation

Gamma

e- Beam

Oxidising Agents Alkylating Agents

H2O2Vapour

H2O2 Vapour(with Plasma)

H2O2 Vapour(with Ozone)

Chlorine Dioxide

Per Acetic Acid Vap (with Plasma)

Ethylene Oxide

LTS withFormaldehyde

Glutaraldehyde

Ozone Gas

In Hospitals Steam is the most prevalent>95% of processes but LTS is required

The many available Sterilization processes for Medical Devices

LTS Utilisation in Health Care

Ethylene Oxide –

• Utilisation in hospitals country specific – Southern Europe high use.

• Many hospitals use contractors such as Anderson Caledonian or Isotron/Synergy/Steris (User remains responsible).

LTSF

• Once virtually every department had an LTS/LTSF sterilizer now hardly any.

Hydrogen Peroxide (VHP)

• “The growing technology”

• Many hospitals now using VHP processes

• Growing application area – endoscopy

• “As the field of endoscopy develops there will be a greater need for sterile endoscopes”

• (paraphrased from Prof Tony Young’s talks at IDSc 2010 conference)

All use a mixture of H2O and H2O2

Vaporized Hydrogen Peroxide SterilizationProcess Temp:30-50oCProcess Time:30 to 100 min

Process Limitations:Restricted Lumen LengthNo PaperMaterial Corrosion

Pressu

re (tor

r)

Cycle Time

Vacuum

An Example STERRAD® 100NX / NX

Vent

Diffusion Diffusion

VH2O2Exposure

“Gas”Plasma 1

“Gas”Plasma 2

VH2O2Exposure

Vent

Vacuum

AUC 1 AUC 2

How does a vH2O2 process work - Surface Effects

Vaporization Condensation

Liquid solution of hydrogen peroxide in water (with stabilizers) Vapour Phase mixture

of hydrogen peroxide and water in the chamber

Vapour and liquid phase on surface of Med Dev. Temperature / Pressure dependent.

What do we need to monitor to ensure efficacy & how?

VH2O2 SterilizationProcess Variables

Time Temperature vH2O2 [c] / Dose (AuC) Moisture

⏲ ?

H2O2 vapour is produced from an aqueous solution so water is present during processing.The importance of its presence is debated.

In a recent publication data was presented to show the influence of the ratio of vH2O2 and vH2O on microbial kill rate (D value) suggesting a 1.4 order of reaction.

Zentrl Sterilization 2021:29(4):222-230

UV Source

UV Detector

Time and Intensity vs “Dose”• Moist Heat• Traditionally a series of

time-temp combinations • 121/15mins (Fo = 15 min)• 134/ 3 mins (Fo = 60 mins)• 132 / 4 mins (Fo = 50 mins)• In contained product sterilization

equivalent time at a reference temperature can be calculated by integrating the area under the T-t curve. This is the dose of moist heat.

• Fo = ∑10 (T-121/z).dt mins

• Irradiation• Absorbed Dose -> An integral

of radiation intensity and time of exposure.

• Measured in kGy representing energy absorbed per unit mass

• Traditionally 25kGy considered a sterilizing dose.

• Delivered dose estimated by dosimetry.

8

VH2O2Many sterilizers calculate the area beneath the exposure curve as mg.s/L annotated AuC or “Dose”

Pres

sure

(tor

r)

Cycle Time

Vacuum

An Example STERRAD® 100NX / NX

Vent

Diffusion Diffusion

VH2O2Exposure

“Gas”Plasma 1

“Gas”Plasma 2

VH2O2Exposure

Vent

Vacuum

AUC 1 AUC 2

60Co

What do we need to monitor to ensure efficacy and how?

VH2O2 Sterilization Process Variables How to Monitor

Physical Measurements

Biological Indicators

Chemical Indicators

Physical Measurements• time,• Temperature • VH2O2 [c]

Biological Indicators:• React to all process

variablesChemical Indicators

• React to a specified range of process variables. The manufacturer states the Stated Values (SV) for these

UV Source

UV Detector

• Type 1 – Process / Exposure Indicators (eg IndicatingTapes, Labels)• Type 2 – Specific Test Indicators (e.g. BDT)• Type 3 – Single variable indicators

• Respond to a single variable in the process e.g. temperature

• Type 4 – Multivariable Indicators• Respond to two or more variables in the process

• Type 5 – Integrating Indicators• Respond in a way which mimics the response of a BI if used in the same process

• Type 6 – Emulating Indicators • Respond to all critical variables of the process at levels associated with acceptable

sterilizing conditions e.g. 134 for 3 minutes

Chemical Indicators – Types - EN ISO 11140-1

Majority of VH2O2 CIs are either type 1 or 4

Chemical Indicator Dosimeters• Irradiation• Polymethylmethacrylate (pmma)

tokens respond in a calibratable manner to allow dose at point of placement to be estimated (Harwell Amber Dosimeters).

• With thank to Harwell Dosimeters11

• Moist Heat• Type 5 moving front chemical

indicators respond in a calibratable manner to allow Fo to be estimated in contained product moist heat sterilization

• (Bunn and Sykes, J Appl Bact 1981,51,143-147)

Can VH2O2 CIs also be used as dosimeters ?

Research Question

• Can VH2O2 CIs perform as dosimeters?• Study Plan:•Using data from previously published data can;

1. the response of type 1 and 4 CIs be calibrated to give dose (mg.s/L) of VH2O2 to which exposed

2. the calibrated CI’s provide an estimate of the dose of VH2O2 delivered during a production sterilization cycle when placed within model medical device instrument sets.

12

Stage 1 – The evaluation of a number of type 1 and 4 vH2O2 CIs

The following results are presented from a paper published in Central Service Journal,Zentr Steril. 2020, 28(4),208-217

A

B

CD

EF

G

H

Products Tested

Mounted on a pre cut acetate sample holder using vH2O2

indicator tape

Placed in the centre of the chamber 100mm above the vaporizer

inlet port

Method – exposure apparatus

Target Peak Concentration vH2O2 mg/L chamber space

Average Concentration vH2O2 mg/L chamber space

Dose vH2O2 mg.s/L chamber space (AuC)

Short dotted line – temp oCLong dotted line – pressure mBSolid line = vH2O2 concentration mg/L

vH2O2Injection

Measurement of Exposure to VH2O2Measurement of concentration and dose (area under the curve mg.s/L)

Measurement of colour change

Colourimetry :Estimation of colour change by measuring L*,a*,b*From which E was calculated; E= L*+a*+b*

Visual Examination

Calibration Curves – AuC (Dose) vs a*, b*or E

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Type 1 CIs

y = -2.907ln(x) + 15.481R² = 0.9692, N=27

y = -0.066ln(x) - 2.6031R² = 0.0004, N=6

-6

-4

-2

0

2

4

6

8

0 200 400 600 800 1000 1200 1400

AuC (mg.s/L)

D

50 C

45 C

a*

y = -17.68ln(x) + 139.75R² = 0.6183, N=3

y = -10.69ln(x) + 87.648R² = 1, N=2

y = -7.637ln(x) + 75.587R² = 0.9797, N=30

20

25

30

35

40

45

50

55

60

0 200 400 600 800 1000 1200 1400

a*

AuC mg.s/L

A

45 C

47 C

50 C

y = 0.0342x - 11.508R² = 0.7357,N=6

y = 0.0099x + 2.6386R² = 0.8073, N=37

0

5

10

15

20

25

30

0 500 1000 1500 2000 2500

b*

AuC (mg.s/L)

C

45 C

47 C

50 C

y = -5.608ln(x) + 34.561R² = 0.9262,N=5

y = -3.768ln(x) + 25.7R² = 0.9852, N=9

0

5

10

15

20

0 100 200 300 400 500 600 700 800

a*

AuC (mg.s/L)

B

45 C

47 C

50 C

Calibration Curves – AuC (Dose) vs E,a*or b*

19

Type 4 CIs

y = 35.496ln(x) - 144.69R² = 0.9914,N=8

y = 27.551ln(x) - 100.32R² = 0.9264,N=14

y = 30.045ln(x) - 107.32R² = 0.9889,N= 38

-20

0

20

40

60

80

100

120

0 200 400 600 800 1000 1200 1400

E

AuC (mg.s/L)

E

45C

47 C

50 C

y = 0.0124x - 19.718R² = 0.6627,N=21

y = 0.0156x - 21.773R² = 0.962,N=11

y = 0.0169x - 22.933R² = 0.9574,N=8

-25

-20

-15

-10

-50 200 400 600 800 1000 1200

b*

AuC (mg.s/L)

F

50 C

47 C

45 C

y = -27.41ln(x) + 242.78R² = 0.8527,N=23

y = -51.77ln(x) + 408.32R² = 0.7509,N=6

y = -10.87ln(x) + 147.54R² = 0.9696,N=11

20

30

40

50

60

70

80

90

100

110

120

0 200 400 600 800 1000 1200 1400

E

AuC (mg.s/L

G

50 C

45 C

47 C

y = 0.0017x - 8.6804R² = 0.4235,N=21

y = 0.0022x - 9.4886R² = 0.2066,N=10

y = 0.0023x - 10.12R² = 0.0169,N=6

-10

-9,5

-9

-8,5

-8

-7,5

-7

-6,5

-60 200 400 600 800 1000 1200 1400

b*

AuC (mg.s/L)

H

50 C

47 C

45 C

The following results are presented from a paper published in Central Service Journal,Zentr Steril. 2020, 28(6),334-343

Stage 2 - Clinical Case Study

Method – model loads tested and placement of CIs

Xi

DV1

DV2

StE/StS

• Tests were carried out in ASP® STERRAD® NX100® VH2O2 sterilizers (https://www.asp.com/product/terminal-sterilization/STERRAD-100nx)

• EXPRESS cycle - maximum loading weight 4.85 kg /10.7lb or • STANDARD cycle – maximum loading weight 9.7kg/21.4lb • Two different sterilization processing departments in hospitals in the USA.• Ten replicate cycles for each load configuration / processing cycle was used

Method – sterilizer used including recommended loads

Method – sterilization process employed

Pressu

re (tor

r)

Cycle Time

Vacuum

An Example STERRAD® 100NX / NX

Vent

Diffusion Diffusion

VH2O2Exposure

“Gas”Plasma 1

“Gas”Plasma 2

VH2O2Exposure

Vent

Vacuum

AUC 1 AUC 2

Dose vH2O2 mg-s/L chamber space (AuC)

Clinical Studies – Predicted vs Measured VH2O2 [c]

24

0

200

400

600

800

1000

1200

1400

1600

1800

900 1000 1100 1200 1300 1400 1500

VH2O

2 Do

se m

g.s/

L pr

edic

ted

by C

I

VH2O2 Dose (AuC) mg.s/L measured by sterilizer

0

200

400

600

800

1000

1200

1400

1600

680 730 780 830 880 930 980

VH2O

2 Do

se m

g.s/

L pr

edic

ted

by C

IVH2O2 Dose (AuC) mg.s/L measured by sterilizer

Key to the colours:Orange = A Blue = E Yellow = B Purple = F Red = C Light Blue = GGreen = D

• Preliminary data suggests that the colour change of some chemical indicators is quantitatively related to the dose of hydrogen peroxide vapour to which they are exposed at a specified temperature.• Calibration curves of a colour change attribute (E, a* or b*) vs

exposure dose (AuC, mg.s/L) can be created with high correlations.• Further data is required across a wider range of exposure doses to

confirm these correlations.• ISO TC 198 wg6 could consider developing a type 5 integrating

indicator category based on dose (mg.s/L) response rather than simple colour change.

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Conclusion 1: Calibrating CIs to Dose

• Since some CIs were shown earlier to change colour in a predictable way towards changing VH2O2 dose;• The CI curves should overlay the black line• Even if offset the CI curves should run parallel to the black curve• The sterilizer measured VH2O2 dose shows great process variability• Some CIs predict higher values of VH2O2 dose and others lower• The predicted VH2O2 dose varies greatly with no overall predictable

trend.• Is this due to CI variability (no) or process variability (yes) due to

fluctuating conditions of VH2O2 [c] and Temp at point of placement?• More experimentation is needed

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Conclusion 2: Use in a clinical setting