Page updated 9 October 2006
Operating a Steriliser and Instrument Sterilisation
- HTM 2010 provides comprehensive guidance on all aspects of sterilisation in the healthcare setting and HTM 2030 on the operative procedures, validation and maintenance of washer/disinfectors . Available at www.dh.gov.uk
- List of small benchtop decontamination equipment (sterilizers and thermal washer disinfectors) that comply with Model Engineering specifications C31 (washer disinfectors) and C15 (benchtop sterilizers) can be found on the NHS Purchasing and Supply Agency website.
Decontamination Stage 2: sterilisation
Sterilizers perform a crucial role in prevention of cross infection. Therefore the benchtop steam sterilizer must be suitable for the intended loads, and must be validated before use , maintained and operated properly to ensure that the load is sterilized on every occasion. Sterilizers are required to operate to HTM2010 specifications and Model Engineering Specification C15.
Periodic testing and Maintenance
You should ensure that all the relevant checks and tests are performed to provide assurance that the sterilizer is safe to use, that it is functioning correctly and that it will sterilize loads consistently. sterilisation is a process whose effectiveness cannot be guaranteed by inspection (autoclave tape) or testing of the product (spore tests). Nor can the effectiveness of the sterilisation process be verified retrospectively by a maintenance engineer's report. For this reason successful sterilisation depends on consistent reproducibility of the sterilizing conditions during every cycle. Process monitoring of individual sterilisation cycles is the approved method for guaranteeing that instruments and equipment are sterile. Microbiological testing of steam sterilizers is not currently recommended for routine use.
Details on how to conduct periodic testing (daily, weekly, quarterly and annual) for non-vacuum and vacuum autoclaves are issued by the MHRA and can be found in MDA DB 2000 (05) and DB 2002 (06).
Suitability of sterilizer for different loads
There are two main types of benchtop sterilizers available for use in the dental surgery, namely the traditional non-vacuum (downward displacement /gravity displacement) sterilizers and the newer vacuum benchtop sterilizers.
Types of Sterilsers
Cycle type |
Air removal |
Load type |
| N |
Passive (gravity displacement) | Solid, non-wrapped |
| B |
Forced air removal Active (vacuum) | All ( drying cycle) |
| S |
Active (vacuum, super-atmospheric pulsing, steam injection through lumen | Only suitable for loads specified by manufacturer |
- Non-vacuum (downward /gravity displacement benchtop steam sterilizers) function by displacing air passively from both the chamber and load with steam generated within the sterilizer chamber or in a separate boiler within the sterilizer's casing. Benchtop steam sterilizers are intended for the processing of equipment for immediate use. Loads packaged after sterilisation for later use are not sterile. This type of sterilizer has certain limitations, see table below .Vacuum benchtop sterilizers (benchtop porous load sterilizers) either B or S type have a vacuum pump or generate a succession of steam pulses to remove air from the chamber and load. All types have:
- A forced air removal stage prior to the sterilizing stage;
- A post-sterilisation drying stage (to ensure that the load is dry before the door is opened, which can prolongs the total cycle time considerably).
Sterilizers (S type) designed specifically for sterilizing dental handpieces are available which employ a pulsed, fractionated cycle for removal of air from the lumen.
- Instruments should be clean and dry prior to sterilisation
- Sterilizers should never be overloaded; steam should be able to circulate freely.
- Instruments should be placed across the tray ribs and should not be touching
- Hinged instruments should be opened
- Bowls, kidney dishes etc. should be inverted and placed at an angle to allow draining and the steam to contact all surfaces of the vessel.
- A logbook must be available for each sterilizer. Record details of all the installation, commissioning and validation, maintenance history, details of breakdowns and time out of action. All records should be kept for 11 years .
- You must perform the daily automatic control test every day that the sterilizer is used. The test results are your evidence that the sterilizer is achieving sterilizing conditions. A print out or a handwritten copy of the results should be kept as a permanent record in the logbook . ( Add sample forms- modified from MHRA DB06)
- Record the cycle number of each batch of instruments processed (ideally this should be recorded in the patients notes for instrument traceability).
- Maximum values of the chamber temperatures and pressures indicated on the gauges
- Holding stage duration in minutes and seconds
- The sterilisation holding time is not less than 3 minutes for a 134 0 C cycle
- The temperature during the hold time is within 134-137 0 C
- A visual display of 'cycle complete' is indicated
- No mechanical or other anomaly is observed
- Record if the test cycle is pass or fail
- Failures must be reported by the sterilizer operator to the Dentist or Practice Manager
- Record the actions taken if the cycle failed or a malfunction occurred.
- Keep a secure, permanent record of the test results in the sterilizer log book (for 11 years) or an electronic record, which should be backed up!
- Should be signed and dated by the operator
- Date and cycle number
- Type of load
- sterilisation cycle selected
- Record as pass or fail
- Chart record for the cycle
- Identity of the operator
- The operator should perform weekly safety checks on the door seal
- Check the security and performance of door safety features.
- Do not open the door while the chamber is pressurised (force on the door is equivalent to ¾ of a tonne or 750 kg).
- Be covered by third party pressure vessel liability insurance
- Sterilizer should be installed and validated by a registered Competent Person (an engineer proficient in testing sterilizers)
- A schedule should be arranged for periodic testing by a qualified Test Person.
- Named person in the practice accountable for it's validation, periodic testing maintenance and use
- Operator must be trained
- Sterilizer must only be used for its intended purpose (solid and unwrapped instruments)
- Wrapped, tubular and textile items should be processed in vacuum autoclave
- Perform and record daily performance tests
- Keep permanent record of every sterilisation cycle; record cycle number of instrument tray in patients notes
- Clean and dry instruments prior to sterilisation
- Do not overload with instruments (place inverted, angled, with hinges open), do not allow to touch.
- Non-wrapped items ideally should be used directly from the sterilizer
- Always use distilled/reverse osmosis or sterile water (pathogen & endotoxin free) in the reservoir; drain down daily or at end of session. Reservoirs (using recycled water) clean, rinse and dry after draining down according to manufacturer's instructions.
- Regularly clean inside and outside of sterilizer
- Perform weekly safety checks of sterilizers pressure safety systems (e.g. door lock and seal)
- Keep logbook of commissioning, validation and maintenance record
- Recycled sterile water in the reservoir must be changed daily or if using reverse osmosis or distilled water at the end of the session (twice daily or 4 hourly). (Some makes of sterilizer only use the water once and it's not recycled)
- Drain down and empty the reservoir at the end of the day
- Then the reservoir should be wiped down with sterile water or 70% alcohol solution (or a disinfectant recommended by the manufacturer) using a disposable lint free cloth, rinse and dry.
Suitability of sterilizer for different loads
Sterilizer Type |
Suitable for sterilizing |
Not suitable for sterilizing |
|
Non-vacuum (Gravity Displacement sterilizer) |
solid devices |
Wrapped devices (or sterilisation pouches) |
|
Vacuum Sterilizer (B or S type) |
Wrapped or unwrapped solid devices |
All ( drying cycle) |
Loading and steam penetration
Steam penetration
The effectiveness of the process depends upon direct contact between the steam and all surfaces of the load. Therefore all items that you intend to sterilize must be clean and dry before you place them in the sterilizer chamber. Contamination with residual tissue, body fluids, oil or other deposits will prevent contact between the steam and the surfaces of the load; or contaminants might become fixed to the instruments and be difficult to subsequently remove. In addition organic debris may also contaminate the reservoir water and encourage bacterial growth. Never sterilize heat labile items or single use items in any type of sterilizer.
Loading
In order to sterilize effectively steam needs to be able to circulate freely. Any air retained within the chamber or load will prevent the steam making direct contact with the instruments, so loading the sterilizer must be done with care. Follow the manufacturer's specific instructions but the following points are standard: -
When selecting the temperature for sterilisation use the highest temperature compatible with the load, normally 134-137 0 C for a holding time of 3 minutes at a pressure of 2.5 bar (usually the default setting on sterilizers).
Operating a non-vacuum sterilizer
Daily tests:
Automatic control test, the test requires the temperature and pressure profiles, and the holding time of the cycle to be compared with the values obtained when the sterilizer was known to be working correctly (i.e. the specific settings for your sterilizer which were calibrated by the engineer at the most recent validation. These will vary slightly for each sterilizer).
You must perform the automatic control test using the sterilizing cycle with the highest temperature compatible with the load (usually 134-137 o C). The test should be performed with an empty chamber. The MHRA in Device Bulletin: MDA DB 2002(06) state that to save time the sterilizer can be run loaded but the load composition should be the same or similar each day. A printer fitted to the sterilizers will record the results of the test for you, providing an accurate, permanent, record and saving your time. If your sterilizer does not have a printer fitted, observe the gauges and record the following during the sterilizing (holding) stage of the cycle:
The test can be considered satisfactory if:
Response to automatic control test:
Test failures
The daily automatic control test results should be viewed as a medico-legal document, it is the only evidence you have that the sterilizer was working and could protect you from litigation. A failure of the automatic control test indicates that the sterilizer is not working correctly. The Dentist should have a written procedure for dealing with test failures and the sterilizer should be withdrawn from service until the problem is rectified and a successful test achieved.
Routine Monitoring
In addition to the periodic tests, routine production cycle tests are recommended by the MHRA for every sterilisation cycle to provide assurance that sterilized loads are consistently produced. If the sterilizer is fitted with a printer such records are generated automatically.
The following information should be recorded:
Cycle record
Weekly Safety Checks
Key points for operating a Non vacuum sterilizer
Operating a vacuum sterilizer
Vacuum benchtop steam sterilizers are more complex to use than the standard sterilizers and validation and maintenance is more costly and time consuming. The current MHRA guidelines (MDA DB 2002(06) recommend the use of vacuum autoclaves for sterilisation of dental instruments with lumens (e.g. dental handpieces, forceps). Details of the test requirements for a vacuum autoclave can be found in the MDA DB 2000 (05) and DB 2002(06) and are not described in detail here ( www.mhra .org.uk See appendix for sample forms ). However, the basic daily tests include a pre-start, daily automatic control check test of the autoclave cycle and steam penetration test the results of which are recorded in a separate log ( paper or electronic) and the data kept for 11 years .
Steam penetration test checks that the air removal stage is effective, and that any residual air and other non-condensable gases (NCG) will not interfere with the sterilisation process. It is essential to perform this test with only the steam penetration test device in the chamber. Anything else in the chamber will disrupt the test and produce an erroneous result . Only use the test pack specified by the manufacturer e.g. Bowie and Dick type or manufacturer's equivalent steam penetration test kit (Helix test).
Weekly (air leakage test, automatic air detection system function test, automatic control test (ACT) and steam penetration test), quarterly and annual tests are required for vacuum sterilizers, which are performed by a Competent Test Person. The user can perform weekly tests if they are suitably trained.
Failure to adhere to current guidance exposes patients and staff to unnecessary risk and has legal implications in the event of a device-acquired infection.
The following is a list of key requirements for effective maintenance. It is not intended as a comprehensive review:
Key requirements for effective vacuum sterilizer maintenance |
|
The sterilizer should be installed and validated by a qualified Competent Person (an engineer proficient in testing sterilizers). |
|
The sterilizer should be installed and validated by a qualified Competent Person (an engineer proficient in testing sterilizers). |
| A schedule should be arranged for periodic testing by a qualified Test Person. Checks should be performed on a quarterly and yearly basis. This contract should be overseen by a nominated person at the practice. |
| A log book should be kept and all tests/checks/repairs recorded (including daily/weekly checks) |
| Daily checks (automatic control test, steam penetration test) are required. These checks can be performed by the owner/user. Training should be provided. |
| Weekly checks, consisting of automatic control test, steam penetration test, air leakage and air detection system function test and weekly safety checks are required. This can also be performed by the owner/user provided adequate training is received. |
| Reservoir: Distilled/reverse osmosis or sterile water for irrigation should be used. Reservoir should be emptied, cleaned and dried daily. Water should not be 'topped up'. |
Use of chemical process indicators (that indicate instruments have been through the sterilizer)
Chemical process indicators include autoclave tape, test tubes containing a chemical indicator, sterilisation packaging or bags. These process indicators are designed to help you distinguish whether an instruments has been through a sterilizer cycle. They offer no guarantee that the instrument is sterile. They are not an alternative to the automatic control test (ACT) or cycle record.
Typically, heat-sensitive chemical indicators react when exposed to steam and demonstrates a change in colour. Indicators must be stored in accordance with manufacturer's instructions under conditions that will not adversely affect the performance of the chemicals. Only use if they are in date.
Maintenance of the water reservoir chamber
All sterilizers have a reservoir chamber from which the water is delivered for steam generation.
The MHRA recommend that water used in the sterilizer water reservoir should be free of minerals that may cause causes scaling of the internal sterilizer pipe work , and to ensure the integrity of the sterilisation cycle it should be free of pathogens and endotoxins (pyrogen) free". The purpose of using endotoxin free water is to prevent contamination of the load with bacterial endotoxins. Endotoxin is a toxic lipopolysaccharide formed by the breakdown of the cell wall of Gram negative bacteria. Bacterial endotoxins are biologically active even when the bacteria from which they are released are dead. Endotoxins are implemented in hypersensitivity reactions, toxic shock and periodontal disease and can inhibit wound healing. Bacteria in the reservoir water are killed during the steam generation process, but the endotoxins released from the bacterial cell walls remain, and as the water in the steam condenses on cooling, it coats the instruments with endotoxin
Ideally use water that is guaranteed by the manufacturer to be free of minerals and endotoxin (pyrogen) such as water sold as sterilized water for irrigation, as recommended by the MDA DB 2002(06) . Reverse osmosis (RO) or distilled water whether produced on site or bought commercially is considered acceptable . However, the microbiological quality of the water deteriorates rapidly on storage so any partially used bottles of water or locally produced water should be discarded at the end of the day.
Daily maintenance of the reservoir:
RO machines and stills need to be maintained and the water periodically sampled and tested for chemical contaminants, mineral content and pH .
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