Sterilization

Information about Sterilization

Published on July 2, 2009

Author: muralicv

Source: authorstream.com

Content

Sterilization : Sterilization Muraleedharan CV Division of Artificial Organs Biomedical Technology Wing SCTIMST, Trivandrum, INDIA Agenda : Agenda Basics Sterility assurance Techniques Validation Disinfection or Sterilisation ? : Disinfection or Sterilisation ? What is the temperature needed to inactivate bacteria ? It depend on the bacteria because some are highly resistant to heat. (Ex.: Geothermal bacteria like hot spring bugs withstand 250 oC ) Most human pathogens were thought to be killed by temperature lower than 150 oC. Disinfection may be defined as: Cleaning an article of some or all of the pathogenic organisms which may cause infection STERILISATION is a process by which living organisms are killed or removed to the extend that they are no longer detected by standard culture media which have previously been found to proliferate Nature of the problem : Nature of the problem Medical devices and appliances that contact blood or other internal tissues are expected to be sterile. Many medical practitioners advocate an absolute concept for sterility to mean the lack of any viable microorganisms on or within the device and the interior of the packaging Most technologists operate from the stand point that sterility of medical product is a probabilistic function. Definitions : Definitions STERILISATION is a process by which living organisms are killed or removed to the extend that they are no longer detected by standard culture media which have previously been found to proliferate. STERILISATION is a process by which anticipated levels of microbial contaminants (bioburden) in a load of items are exposed to that lethality of sterilising condition, so that the probability of survivor per item (PSI) is less than a specified value. Effectiveness of sterilization : Effectiveness of sterilization ? Initial bioburden in the load ? Lethality of the sterilising condition Duration of process LETHALITY : Steam - Temperature / pressure ETO - ETO Concentration, Temp, %RH Radiation - Dosage rate Chemical - Concentration, Temperature Sterility Assurance Level (SAL) : Sterility Assurance Level (SAL) Expressed either as Probability of Survivor per Item (PSI) or as Microbial Survivor Index (MSI) PROBABILITY OF SURVIVOR PER ITEM (PSI) : PSI of 10-6 indicates that One in a million packages can contain one viable microorganism after sterilisation MICROBIAL SURVIVOR INDEX (MSI) : MSI is derived by taking the reciprocal of the logarithm of PSI Different devices may require different levels of Sterility Assurance Levels Process Design : Process Design Max. Bioburden in the load = 106 CFU per pack SAL required (PSI) = 10-6 Load pre-warming period = 30 minutes Post flushing period = 90 minutes D-Value = 2.5 minutes Total exposure duration required = 12 x D minutes = 30 minutes(6D for reducing the bioburden to unity and 6D for attaining PSI of 10-6) Total process duration = 30 min + 30 min + 90 min = 150 minutes Sterilization Techniques : Sterilization Techniques Steam Ethylene Oxide Dry heat Radiation Chemical Filtration Plasma Pulsed light .. Steam : Steam Most reliable and practical Rapid acting sterilant Factors influencing the process(Temperature, time , penetration) Standard cycles 121°C / 15 psig; 20-30 minutes132 °C / 28 psig; 5-10 minutes Shortcomings : High temperature (polymers) large thermal cycling (polymers) Drying / Handling Dry heat : Dry heat Suitable for metallic / ceramic devices High temperature process Factors influencing the process(Temperature, time) Standard cycles 160°C ; 1 - 2 hours180°C ; 30 - 45 minutes Shortcomings : High temperature Slow ETO : ETO Economical and popular Low temperature process Factors influencing the process(ETO Conc., temp., %RH, time) Standard cycles 600 mg/L ETO, 60% RH, 55°C, 2 Hours(100 % ETO / ETO-Freon / ET-CO2 mixtures) Shortcomings : Residual ETO Formation of EG / ECH Long aeration cycles Radiation : Radiation Most reliable and effective Excellent penetrating power Factors influencing the process(Energy level, time) Radiation sources Gamma (Co-60, Ce-137), Beta (Electron accelerateors) Dosage Levels1 Mrad for MSI = 3, 1.6 - 2 Mrad for MSI = 6Normally used max dosage = 2.5 Mrad ShortcomingsLarge initial investment, Not suitable for many polymers Chemicals : Chemicals Formaldehyde solution / vapour Peracetic acid Ethylene oxide solution Beta-propiolactane Gluteraldehyde solution Ozone . . Plasma : Plasma Glow discharge plasma (low temp.) Hydrogen peroxide precursor Free radicals and ions interact withliving organisms and destroys them Ideal for industrial applications Penetration of precursor is critical Minimal residuals as very low concentration are used Cleanliness of the device / package is critical Pulsed Light : Pulsed Light Wide spectrum pulsed light Ultraviolet to infrared 20,000 times brighter than sunlight 0.1 to 2 J/cm2 energy levels per flash 1 to 12 J/cm2 energy dosage levels Very fast and economical No residuals Ideal for transparent packaging Not fully evaluated for material damage STERILISATION VALIDATION : STERILISATION VALIDATION Installation qualification Process validation Process monitoring Indicators are used for process validation as well as process monitoring Chemical Indicators (CIs) : Chemical Indicators (CIs) Except for wax, most CIs are based on a pH change resulting from organic acid evaporation by heat and revealed by a colorimetric indicator The oldest CI Pb + S + H PbS The reaction do not occur without heat Indicators : ISO Class 11140-1 : Indicators : ISO Class 11140-1 Class 1 : External indicator charged to signal if the pack has been exposed or not. Example : autoclave tape. Class 2 : Indicator for a specific parameter - Qualitative Example : Bowie Dick (vaccum à 121 oC) Before Use Incorrect Change Correct Change Indicators : ISO Class 11140-1 : Indicators : ISO Class 11140-1 Class 3 : Indicator for a unique parameter - Quantitative Example (s) : Melting wax pellet at 121 oC Colour change crayons Mostly used for validating temperature distribution in steam sterilisation chambers. Indicators : ISO Class 11140-1 : Class 4 : Indicator sensitive to 2 parameters (ex.: time and temperature) within 25 % of expected targets. For class 4 and higher, indicators must change abruptly The change of color must happen within 25 % of the expected time and within 2 oC Example : An indicator that accept (OK or Pass) at 132oC pour 4 min. MUST reject (Fail) a 130oC for 3 minutes. Indicators : ISO Class 11140-1 Indicators : ISO Class 11140-1 : Class 5 : An indicator / integrator sensitive to 2 or more parameters, and reacting within 15 % of expected targets. In this category, the change of color must be abrupt, happens within 15 % of expected targets and MUST NOT happen if the targeted temperature is not achieved within 1oC. Example : An indicator that accept (OK or Pass) at 132oC for 4 min MUST reject  (Fail) a 131oC for 3 minutes and 22 seconds. Indicators : ISO Class 11140-1 Indicators : ISO Class 11140-1 : Classe 6 : An indicator / integrator sensitive to 2 or more parameters, and reacting within 6 % of expected targets. In this category, the change of color must be abrupt, happens within 6% of expected targets and MUST NOT happen if the targeted temperature is not achieved within 1oC. Example : An indicator that accept (OK or Pass) at 132oC for 4 min MUST reject  (Fail) a 131oC for 3 minutes and 45 seconds. Indicators : ISO Class 11140-1 Biological Indicators : Contains specific bacterial spores with known concentration, with or without culture media Steam Bac. Stearothermophilus ETO Bac. Subtilis var. niger Radiation Bac. pumilus Biological Indicators Slide 25:  Thank You

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