SN 2002(24) - Steam penetration tests in vacuum benchtop sterilizers

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August 2002

MANUFACTURER/SUPPLIER
Various

PROBLEM
A daily steam penetration test is necessary to assist in the demonstration of the effectiveness of vacuum benchtop sterilizers that process wrapped, textile, hollow or tubular loads. Manufacturers of various sterilizers on the market do not provide information on the type of steam penetration test that is suitable and validated for their particular sterilizer. This could lead to failure to sterilize loads.

For the attention of:

NHS Trusts (England) - Chief Executives
National Care Standards Commission - Headquarters
Primary Care Trusts (England) - Chief Executives

ACTION
If you have a vacuum (forced air removal) benchtop sterilizer that processes wrapped, textile, hollow or tubular medical devices:

• ensure that a daily steam penetration test is carried out in accordance with the manufacturer's instructions
• if there is no test available , do not use the sterilizer for processing any wrapped, textile, hollow or tubular medical devices. Use these sterilizers only for non-wrapped, solid devices.

If you are considering purchasing a vacuum (forced air removal) benchtop sterilizer that processes wrapped, textile, hollow or tubular medical devices:

• ensure that a validated daily steam penetration test is available for the sterilizer
• if there is no test available, do not use the sterilizer for processing any wrapped, textile, hollow or tubular medical devices. Use these sterilizers only for non-wrapped, solid devices.
• MDA DB2000(05) has further information on points to consider.

Note: The term wrapping includes pouches and sterilization bags.

DISTRIBUTION REQUIRED
Please bring this notice to the attention of all who need to know or be aware of it. This will include distribution by:

TRUSTS to:

• Liaison Officers (for onward distribution)
• Accident and Emergency Departments
• Infection Control Doctors
• Infection Control Nurses
• Managers of all departments using benchtop (transportable) steam sterilizers
• Medical Directors
• Nurse Executive Directors
• Theatre Managers

NATIONAL CARE STANDARDS COMMISSION to:

• Headquarters (for onward distribution)
• Practice Nurses
• Care Homes providing personal care
• Care Homes providing nursing care
• Domiciliary Care
• Hospices
• Hospitals in the Independent Sector

PRIMARY CARE TRUSTS to:

• Liaison Officers (for onward distribution)
• General Medical Practitioners
• General Dental Practitioners

BACKGROUND
Since publication of SN2001(34), we have become aware that various other manufacturers' models of vacuum benchtop steam sterilizers do not have the means to demonstrate the effectiveness of steam penetration into the sterilizer load.

Type B or Type S sterilization cycles (see explanatory note) are intended to process loads that can retain air. They usually have a vacuum pump to remove the air. Pressurized steam is an effective sterilizing agent provided that air has first been removed from the sterilizer chamber and load. Residual air can prevent direct contact between the steam and the devices to be sterilized. An effective vacuum air removal stage is required to remove air from loads that are wrapped, textile, hollow or tubular. Some sterilizers incorporate means (including a steam penetration test) to detect residual air, which will prevent sterilization.

Vacuum steam sterilizers should also be tested at the start of each day the sterilizer is used in order to check that the air removal stage is effective. This is termed the steam penetration test, which has to be validated to each specific sterilizer type to demonstrate that it can detect air that is present in sufficient quantity to interfere with sterilization. Some sterilizer manufacturers do not provide an acceptable test method for doing this.

In the absence of steam penetration tests there can be no certainty that the sterilizer is achieving sterilizing conditions. Therefore it should be used in the same way as a traditional benchtop steam sterilizer, applying the appropriate daily and other periodic test procedures, and only used to sterilize non-wrapped solid devices.

To produce sterile products consistently, benchtop steam sterilizers should be tested according to the protocols provided in Health Technical Memorandum (HTM) 2010, Part 3 Validation and verification *, which are summarized in MDA's device bulletin DB9605 - The purchase, operation and maintenance of benchtop steam sterilizers, or DB2000(05) - The purchase, operation and maintenance of vacuum benchtop steam sterilizers. Appendix 1 sets out some good practice points based on those in DB2000(05).

Explanatory Note: Type N sterilization cycles and traditional benchtop sterilizers do no use vacuum assisted air removal and should not therefore be used to process instruments that have been wrapped, or are hollow or tubular in construction. Type B sterilization cycles are intended to process porous loads e.g. wrapped instruments and fabrics. Type S sterilization cycles are designed to process air retentive loads e.g. tubular devices, as specified by the sterilizer manufacturer.

ENQUIRIES
Enquiries to the MHRA should quote reference number 20020206.025-6

 

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Appendix 1
Ten good-practice points for the use of benchtop steam sterilizers
[extracted from MDA DB 2000(05)]

• Where possible, use a sterile service facility rather than processing locally.
• Do no process wrapped, tubular or textile products in a conventional benchtop steam sterilizer - process them only in a suitable vacuum benchtop steam sterilizer.
• All items must be clean and dry before loading into the sterilizer. Do not overload the sterilizer - the load items might not be sterilized.
• Sterilization performance must be checked frequently (daily [this includes the steam penetration test on vacuum benchtop sterilizers] and weekly by the user; quarterly and annually by a competent test person). Keep written records. This is in addition to routine maintenance and cleaning.
• Drain and clean chamber and reservoir at the end of each day and leave dry. Replenish with sterile water for irrigation from an unopened container.
• Have the sterilizer's pressure system checked for safety. Keep records of all checks and repairs to the pressure system. This is a legal requirement. Do not circumvent safety features.
• Keep permanent records of every sterilization cycle.
• Keep written records of all testing and maintenance carried out on every sterilizer. The records should be kept in a logbook.
• Technical advice is available from Registered Authorised Persons (Sterilizers) [AP(S)]. Infection Control Nurses can advise on prevention of cross infection. Consult them if you are not sure how to sterilize a piece of equipment.
• Never re-process single use devices.

©Crown Copyright 2002