Sterilisation
Sterilisation
by steam
Instruments can be sterilised by steam under pressure using autoclaves.
Vegetative bacteria, including tuberculosis, and viruses such as hepatitis B,
hepatitis C and human immunodeficiency virus (HIV) and heat-resistant spores,
including Clostridium tetani and Clostridium perfringens, are
killed. The combination of pressure, temperature and time with the moist heat is
important:
• 1340C (30 lb/in.2) for a hold time of 3
minutes;
• 1210C (15 lb/in.2) for a hold time
of 15 minutes;
• prepacked materials and instruments are processed through a
porous load autoclave which incorporates a prevacuum cycle necessary to extract
air. If this is not achieved then the dried saturated steam cannot penetrate
efficiently. Unwrapped instruments can be sterilised in a small autoclave within
the theatre precinct, which is convenient when instruments are dropped.
Monitoring
All autoclaves must be regularly maintained according to the
manufacturer’s instructions, and a record should be kept of the cycle time,
the prevacuum phase, the pressure and temperature. In addition, the steam
penetration test (Bowie—Dick test) and chemical indicators, for example
Brownes tubes or impregnated tapes, are used to ensure that such errors as poor
packing do not prejudice the efficiency of the process. Biological indicators
are not appropriate.
Sterilisation
by ethylene oxide
Ethylene oxide is a highly penetrative noncorrosive gas which has a
broad-spectrum cidal action. It is utilised for heat-sensitive materials
including electrical equipment. It is not recommended for ventilator respiratory
equipment or soiled instruments because organic debris, including serum, has a
marked adverse effect.
Sterilisation
by hot air
This is inefficient compared with moist steam sterilisation, but it has
the advantage in the ability to treat solid
Sterilisation
by low-temperature steam and formaldehyde
This uses a combination of dried saturated steam and formaldehyde,
with the main advantage being that sterilisation is achieved at a low
temperature (730C) and the method is therefore suitable for
heat-sensitive materials and items of equipment with integral plastic
components. It is not recommended for sealed, oily items or those with
retained air. Some plastics and fabrics absorb formaldehyde, releasing this in a
delayed manner which may cause hypersensitivity to the users.
Sterilisation
by irradiation
This technique employs gamma rays or accelerated electrons. It is an
industrial process and is particularly appropriate to the sterilisation of large
batches of similar products, such as syringes, catheters and intravenous
cannulas. The delivery of an irradiation dose in excess of 25 kGy is accepted as
providing adequate sterility assurance.