Working of Steam sterilizer or autoclave

This presentation is about steam sterilizers or autoclaves used in hospital CSSD
#cssd #hospital #CDC

1. Autoclave / Steam sterilizer Dr. Abhijeet Mane Associate Professor (Microbiology) Co-Ordinator (Infection Control) 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 1

2. Flow of presentation Historical aspect Sterilization Types Factors critical to assure successful steam sterilization Sterilization control Common mistakes in steam sterilization 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 2

3. Sterilization A process by which an article, surface or medium is rendered free from all microorganisms including spore state Types Moist heat sterilization Temperature below 100 deg C Temperature at 100 deg C Temperature above 100 deg C – Autoclave / steam sterilizer Dry heat sterilization Chemical sterilants 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 3

4. Autoclave / Steam sterilizer Historical aspect French Physicist - Denis Papin Invented Steam Digester (1679) To extract fat from bones To make bone meal First actual autoclave - created by Charles Chamberland (1879) 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 4

5. Autoclave / Steam sterilizer Principle Moist heat destroys microorganisms by the irreversible coagulation, denaturation of enzymes and structural proteins Basically a chamber that can withstand pressures of greater than 2 atmospheres Steam under pressure (in-short) Converts water to steam and holds the steam just below boiling point (saturated) so that there is a maximum (latent) heat held in a semi-gaseous state Steam contacts the load in the chamber, releases heat, results in sterilization Steam sterilization as a rule, uses far less energy and time than dry-heat methods 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 5

6. Autoclaves / Steam sterilizers Pressure chamber A large cylinder (vertical or horizontal) made up of gun metal/steel A steam jacket – water compartment Lid A discharge tap for passage of steam and air A pressure gauge A safety valve Electrical heater Heats water to produce steam 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 6

7. Procedure Sterilization process can be divided in 3 phases Conditioning phase – air removal Exposure phase (sterilize) – holding period Exhaust phase (dry) – sterilizer allowed to cool 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 7

8. Autoclaves / Steam sterilizers Advantages Cheap, low cost than ETO and plasma sterilization Cycles fast compared to ETO Non toxic Disadvantages Unsuitable for anhydrous materials (e.g. oils, powders), wood, and for heat- and moisture-sensitive materials May leave instruments wet, causing them to rust Deleterious for heat-sensitive instruments Microsurgical instruments damaged by repeated exposure Potential for burns 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 8

9. Types of Autoclaves / Steam sterilizers Downward (gravity) displacement sterilizers Steam pulsing autoclaves High-vacuum autoclaves 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 9

10. Downward (gravity) displacement sterilizers Steam introduced from the top of the chamber Removes the cooler and denser air-steam mixture from the bottom of the chamber Drawbacks Complete air removal is not guaranteed Affects steam penetration of the load Designed for sterilizing bio-hazard waste, solutions and instruments. 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 10

11. Steam pulsing autoclaves Removes air rapidly by repeatedly alternating a steam flush and a pressure pulse above atmospheric pressure. Air is rapidly removed from the load as with the prevacuum sterilizer 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 11

12. High-vacuum autoclaves Fitted with a vacuum pump (or ejector) to ensure air removal from the sterilizing chamber and load before the steam is admitted. Advantage - nearly instantaneous steam penetration even into porous loads. 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 12

13. IMMEDIATE USE SYSTEM STERILIZATION (IUSS) / “FLASH” STERILIZATION Modification of conventional steam sterilization Fast sterilization – 134 deg C for 3-10 minutes Surgical instruments in unwrapped condition Not suitable for porous / cannulated instruments , implants Best avoided - as the material is sterilized without packaging and the cycle eliminates drying. As a result, the possibility of recontamination of the material increases 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 13

14. Sterilization control The performance of steam sterilisers can be accessed using various methods like – Physical indicators Digital displays, printouts Chemical Indicators External pack, Bowie Dick Biological indicators Spores of Geobacillus stearothermophilus 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 14

15. Factors critical to assure successful steam sterilization Time Temperature Direct steam contact Air removal Moisture Drying 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 15

16. Time Exposure (sterilization) time is important because all microorganisms do not die at same time Geobacillus stearothermophilus spores - extremely resistant D- value (decimal reduction time) – Time to reduce microbial population by 90% Sterility Assurance level (SAL) - the probability of a single viable microorganism occurring in or on a product after sterilization. The internationally accepted definition of sterility of medical devices allows for the maximum probability of finding one viable organism on a sterilized medical device to be 1/1,000,000, or a SAL of 1 × 10 -6 . Medical devices that will contact sterile tissues (e.g., implants, surgical drains, surgical instruments) are required to be sterilized to this level 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 16

17. Temperature Critical factor Increase temperature, reduces time to sterilization SAL 10 with starting population of 10 6 , D 121C value 2.0 minutes is 12 minutes 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 17

18. Direct steam contact Condensation has 3 effects Wets microorganisms and provides necessary conditions for killing Liberates latent heat Causes significant contraction of steam drawing more steam to site Hence, steam should be able to touch load directly Air removal Air is biggest deterrent to steam sterilization 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 18

19. Moisture Saturated, dry, pure steam Saturated – free molecular balance with water from which it is formed Dry – free from suspended droplets of condensed water Dry saturated steam recommended for steam sterilization (dryness fraction ≥97%) Pure – free from admixture with air or other non condensable gases Superheated steam – steam at temperature too high for its pressure, behaves as dry gas Fails to condense as it cools on load, moisturizing and latent heat effects are lost Sterilizer jacket temperature should be always set below chamber temperature to avoid superheated steam 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 19

20. Drying Wrapped items must be dry before removing from chamber Presence of condensation (wet packs or pouches) can cause re-contamination 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 20

21. Common mistakes in steam sterilization Pouched or heavily wrapped items are tightly packed in chamber Air maybe trapped in items Heavier items placed on top shelves Condensation natural result of steam contact Will fall from shelf to shelf Denser load will create more condensate Hence place heavier items on bottom shelf 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 21

22. 3. Load too dense or items positioned incorrectly Items should be positioned so that condensate is allowed to flow downward 4. Pouches are placed flat on sterilizer shelves or stacked on top of one above other Pouches to be placed vertical Pouches should not be overloaded 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 22

23. 6. Using hard water for steam sterilizer Calcium and magnesium ions present Reduces the heat conductivity It damages instruments Lime, rust, chlorine and salt can all be left as deposits on devices if demineralized water is not used. Lead to stress corrosion, pitting and discoloration of the device. Hence, organisms can readily accumulate and be protected from the killing effects of the steam process 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 23

24. References Decontamination and Reprocessing of Medical Devices for Health-care Facilities (2016) World Health Organization, Geneva Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008 (updated June 2024) https://www.cdc.gov/infection-control/hcp/disinfection-and-sterilization/index.html Marcel Dion Wayne L. Parker (2013) Steam Sterilization Principles & Co- mmon Mistakes Using Autoclaves. Pharmaceutical Engineering November/December 2013 https://ispe.org/ pharmaceutical-engineering/november-december-2013/steam-sterilization-principles Mackie and McCartney. Practical Medical Microbiology 14/e Apurba Sastry. Essentials of Medical Microbiology 3/e 22 November 2024 Autoclave / Steam sterilizer MICROCON 2024 24

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