16. Can Hydrogen Peroxide Sterilization Chemical Indicators be used to estimate the sterilant dose delivered to instrument sets? Preliminary Findings
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(2) Contents 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 2.
(3) The many available Sterilization processes for Medical Devices. Sterilization Processes used for Medical Devices Sterilization Processes. Mechanical Removal (Filtration). Physical Hot. Cold. Moist Heat (Steam). Dry Heat. In Hospitals Steam is the most prevalent >95% of processes but LTS is required. Chemical Oxidising Agents. Alkylating Agents. UV Light. H2O2 Vapour. Ethylene Oxide. Ionising radiation. H2O2 Vapour (with Plasma). LTS with Formaldehyde. Gamma. H2O2 Vapour (with Ozone). Glutaraldehyde. e- Beam. Chlorine Dioxide Per Acetic Acid Vap (with Plasma) Ozone Gas.
(4) 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).
(5) Vaporized Hydrogen Peroxide Sterilization Process Temp: 30-50oC Process Time: 30 to 100 min. An Example STERRAD® 100NX / NX Vent. Diffusion. Diffusion Vent. Pressure (torr). Process Limitations: Restricted Lumen Length No Paper Material Corrosion. All use a mixture of H2O and H2O2. Vacuum. Vacuum. VH2O2 Exposure. VH2O2 Exposure. AUC 1. AUC 2. “Gas” Plasma 1. Cycle Time. “Gas” Plasma 2.
(6) How does a vH2O2 process work - Surface Effects. Condensation. Vaporization. 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..
(7) What do we need to monitor to ensure efficacy & how? H2O2 vapour is produced from an aqueous solution so water is present during processing. The importance of its presence is debated.. VH2O2 Sterilization Process Variables Time. ⏲. vH2O2 [c] / Dose (AuC). Temperature. UV Source. Moisture. UV Detector. ?. 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.
(8) Time and Intensity vs “Dose” • Irradiation. • Moist Heat. • Absorbed Dose -> An integral of radiation intensity and time of exposure.. • Traditionally a series of time-temp combinations • 121/15mins (Fo = 15 min). • Measured in kGy representing • 134/ 3 mins (F = 60 mins) o energy absorbed per unit mass • 132 / 4 mins (Fo = 50 mins) • Traditionally 25kGy considered • In contained product sterilization a sterilizing dose. equivalent time at a reference • Delivered dose estimated by temperature can be calculated by dosimetry. integrating the area under the T-t curve. This is the dose of moist heat. • Fo = ∑10. (T-121/z).dt. An Example STERRAD® 100NX / NX. mins. Vent. Diffusion. Diffusion Vent. Pressure (torr). 60Co. VH2O2 Many sterilizers calculate the area beneath the exposure curve as mg.s/L annotated AuC or “Dose”. Vacuum. Vacuum. VH2O2 Exposure. VH2O2 Exposure. AUC 1. AUC 2. “Gas” Plasma 1. Cycle Time. “Gas” Plasma 2. 8.
(9) What do we need to monitor to ensure efficacy and how?. VH2O2 Sterilization Process Variables How to Monitor Physical Measurements UV Source. Biological Indicators UV Detector. Chemical Indicators. Physical Measurements • time, • Temperature • VH2O2 [c] Biological Indicators: • React to all process variables Chemical Indicators • React to a specified range of process variables. The manufacturer states the Stated Values (SV) for these.
(10) Chemical Indicators – Types - EN ISO 11140-1 • 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. Majority of VH2O2 CIs are either type 1 or 4.
(11) 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).. • 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 •. • With thank to Harwell Dosimeters. (Bunn and Sykes, J Appl Bact 1981,51,143-147). Can VH2O2 CIs also be used as dosimeters ? 11.
(12) 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.
(13) 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.
(14) Products Tested G C. D. A. B. H. F E.
(15) Method – exposure apparatus Placed in the centre of the chamber 100mm above the vaporizer inlet port. Mounted on a pre cut acetate sample holder using vH2O2 indicator tape.
(16) Measurement of Exposure to VH2O2 Measurement of concentration and dose (area under the curve mg.s/L) Target Peak Concentration vH2O2 mg/L chamber space Average Concentration vH2O2 mg/L chamber space Dose vH2O2 mg.s/L chamber space (AuC) vH2O2 Injection Short dotted line – temp oC Long dotted line – pressure mB Solid line = vH2O2 concentration mg/L.
(17) 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.
(18) Calibration Curves – AuC (Dose) vs a*, b*or E y = -17.68ln(x) + 139.75 R² = 0.6183, N=3 y = -10.69ln(x) + 87.648 R² = 1, N=2 y = -7.637ln(x) + 75.587 R² = 0.9797, N=30. 50 45 40. y = -5.608ln(x) + 34.561 R² = 0.9262,N=5. 15. 45 C. a*. 55. a*. B. Type 1 CIs 20. A. 60. y = -3.768ln(x) + 25.7 R² = 0.9852, N=9 45 C. 10. 47 C. 47 C. 50 C. 35. 50 C 5. 30 25. 0. 20 0. 200. 400. 600. 800. AuC mg.s/L. 1000. 1200. 0. 1400. C. 30. 200. 300. 400. AuC (mg.s/L). D. 8. 25. 47 C. 10. y = 0.0342x - 11.508 R² = 0.7357,N=6 y = 0.0099x + 2.6386 R² = 0.8073, N=37. 5 0 0. 500. 1000. 1500. AuC (mg.s/L). 2000. 2500. 700. 800. 2. a*. 45 C. 600. y = -0.066ln(x) - 2.6031 R² = 0.0004, N=6. 4. 15. 500. y = -2.907ln(x) + 15.481 R² = 0.9692, N=27. 6. 20. b*. 100. 50 C. 0 0. 50 C. 200. 400. 600. 800. 1000. 1400 45 C. 1200. -2 -4 -6. 18 AuC (mg.s/L).
(19) Calibration Curves – AuC (Dose) vs E,a*or b* E. 120. Type 4 CIs 0. F. -5. 200. 400. 600. 800. 1000. 1200. 100 -10. 80. y = 35.496ln(x) - 144.69 R² = 0.9914,N=8 y = 27.551ln(x) - 100.32 R² = 0.9264,N=14. 40 20. 47 C. 0. 200. 400. -20. 600. 800. 1000. 1200. G. 100. -25. 70. AuC (mg.s/L). -6 -6,5. 0. 200. 400. 600. H. 800. 50 C 45 C. 50. 47 C. -8. 40. -8,5. y = 0.0017x - 8.6804 R² = 0.4235,N=21. -9,5. 30. -10. 20 400. 600. 800. AuC (mg.s/L. 1000. 1200. 1400. y = 0.0023x - 10.12 R² = 0.0169,N=6 y = 0.0022x - 9.4886 R² = 0.2066,N=10. -9. 200. 1200. -7,5. 60. 0. 1000. -7. b*. y = -27.41ln(x) + 242.78 R² = 0.8527,N=23. 80. 45 C. y = 0.0124x - 19.718 R² = 0.6627,N=21. y = -10.87ln(x) + 147.54 R² = 0.9696,N=11. 90. 47 C. y = 0.0156x - 21.773 R² = 0.962,N=11. 1400. y = -51.77ln(x) + 408.32 R² = 0.7509,N=6. 110. 50 C. y = 0.0169x - 22.933 R² = 0.9574,N=8. -20. AuC (mg.s/L). 120. -15. 50 C. y = 30.045ln(x) - 107.32 R² = 0.9889,N= 38. 0. E. 45C. b*. E. 60. 1400. AuC (mg.s/L). 19. 50 C 47 C 45 C.
(20) Stage 2 - Clinical Case Study The following results are presented from a paper published in Central Service Journal, Zentr Steril. 2020, 28(6),334-343.
(21) Method – model loads tested and placement of CIs. Xi. DV1. DV2. StE/StS.
(22) Method – sterilizer used including recommended loads • 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.
(23) Method – sterilization process employed An Example STERRAD® 100NX / NX Vent. Diffusion. Diffusion. Pressure (torr). Vent Vacuum. Vacuum. VH2O2 Exposure. VH2O2 Exposure. AUC 1. AUC 2. “Gas” Plasma 1. Cycle Time. Dose vH2O2 mg-s/L chamber space (AuC). “Gas” Plasma 2.
(24) Clinical Studies – Predicted vs Measured VH2O2 [c] Key to the colours: Blue = E Purple = F Light Blue = G. 1800. 1600. 1600. 1400. VH2O2 Dose mg.s/L predicted by CI. VH2O2 Dose mg.s/L predicted by CI. Orange = A Yellow = B Red = C Green = D. 1400 1200 1000 800 600. 1200. 1000. 800. 600. 400. 400. 200. 200 0 900. 1000. 1100. 1200. 1300. VH2O2 Dose (AuC) mg.s/L measured by sterilizer. 1400. 1500. 0 680. 730. 780. 830. 880. VH2O2 Dose (AuC) mg.s/L measured by sterilizer. 930. 24. 980.
(25) Conclusion 1: Calibrating CIs to Dose • 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.. 25.
(26) Conclusion 2: Use in a clinical setting • 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 26.
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