Steam sterilisation is the method of choice for sterilising reusable medical devices. However, it is not suitable for sterilising devices (e.g. fibreoptic endoscopes) that cannot withstand exposure to temperatures of 121 to 138°C at pressure higher than atmospheric. Steam sterilisation is achieved through direct contact of the device with pure dry saturated steam at the required temperature for the required time, in the absence of air.
The design and use of steam sterilisers has to meet the Pressure Equipment Regulations and the Pressure Systems Safety Regulations, which require periodic inspection of the pressure system to ensure its safety16-17. The Provision and Use of Work Equipment Regulations require adequate training of the operator18.
Wherever practicable, the Sterile Services Department should carry out sterilisation. However, in the absence of a central sterilising service, a benchtop steam steriliser may be used, provided it is validated, maintained and operated correctly and according to Device Bulletin 2002(06)18,19. Refer to Benchtop steam sterilisers for further information.
Sterilisation can be achieved using the following combinations of time and temperature15.
|
Table 3: Recommended times and temperatures for steam sterilisation
|
|
Sterilisation temperature
(°C) |
Maximum allowable temperature
(°C) |
Minimum holding time
(minutes) |
|
115 |
118 |
30 |
|
121 |
124 |
15 |
|
126 |
129 |
10 |
|
134 |
137 |
3 | |
You should use the higher temperature of 134 °C for three minutes, provided the medical device will withstand the temperature and associated pressure.
In the simplest type of steam steriliser (known as a downward displacement steriliser) air is removed by displacing it with steam. You can only use this sort of steriliser to sterilise unwrapped, non-porous medical devices. It is not suitable for sterilising the lumens of tubular devices or hollow devices.
A porous load steam steriliser incorporates a vacuum assisted air removal stage prior to steam admission. An air detector monitors the efficiency of the air removal process. You can use this type of steriliser to sterilise wrapped and porous items.
For both types of machine, you must take care to load the steriliser to ensure optimal sterilising conditions. Always follow the manufacturer’s instructions.
The quality of the steam can have a major influence on the efficacy of the sterilisation process. Impurities in the steam can have adverse effects on patients, equipment and the steriliser itself. Health Technical Memorandum 2031 provides advice on the generation, validation and periodic testing of steam supplies20. For smaller, benchtop steam sterilisers, the minimum water quality should be ‘water for irrigation BP’. The reservoir must be emptied at least daily and left dry overnight.