Sterilisation: definition according to European standards
Sterilisation is a chemical or physical procedure aimed at destroying any living organism, pathogenic or not, present in vegetative or spore form on the surface of a material to be sterilised.
The European standard UNI EN 556-1:2002 defines the sterility assurance level SAL or sterility safety standard:
- an item is considered sterile when the probability of finding a living microorganism is 1 in a million (10-6).
- sterilisation operations must be performed with repeatable, standardisable, verifiable and documentable methods.
Surgical instrument reconditioning steps
Sterilisation is the final outcome of the reconditioning process of surgical instruments performed between uses. However, what happens before and after the sterilisation cycle is of primary importance.
In our presentation, we will divide for convenience the reconditioning process of surgical instruments into ten steps:
- Collection of instruments
It is the orderly and separate removal of surgical instruments from the operating theatre to the sterilisation line.
- Disinfection
Disinfection can be carried out manually or by means of thermal disinfectors. In manual disinfection, the choice of disinfectant formulations must take into account their effectiveness against biological risk agents and compatibility with the materials to be treated. In automatic disinfection the material, placed inside the device, follows a specific disinfection program.
Disinfection aims to reduce the microbial count and ensure safer manipulation in the subsequent steps.
- Cleaning
It consists in the removal and elimination of any organic material and part of the microorganisms from a decontaminated instrument.
It can be performed either:
- manually (with a brush, detergent and running water)
- or by using ultrasound equipment (for a cavitation process followed by rinsing)
- Rinsing
The manual cleaning procedure must be followed by rinsing, carried out by showering the items first with running water and then with demineralised water, to remove any residual detergent left on the instruments.
- Drying
It can be done:
- manually with fabric cloths and paper roll
- using machines (such as thermal disinfectors) to complete the washing and disinfection cycle with hot air drying
- Inspection and maintenance
This is the step preceding packaging: the materials must be carefully checked in all their parts, to ensure their efficiency and integrity, and ensure their suitability for surgical purposes. If rotating instruments are to be processed, they must be lubricated.
- Packaging
It is used to preserve instrument sterility until the time when the instrument is used again. Sterility is guaranteed by wrapping the instruments in pre-packaged bags sealed by a heat sealer.
The envelopes have different sizes, weights and life expectancy.
- Sterilisation in autoclave
For the sterilisation of surgical instruments, saturated steam under pressure is used, which allows temperatures of over 100 degrees to be reached.
Commonly called an autoclave, this equipment has a perfectly sealed and pressure-resistant chamber and operates in the following 5 steps:
- The pre-vacuum step is the preliminary phase.
A vacuum pump takes in any air present in the sterilisation chamber, since air in the chamber acts as an insulating barrier, preventing uniform diffusion of the steam.
- Fractional vacuum step.
After bleeding all air, steam is introduced inside the chamber and air replacement with steam takes place in several stages - hence the name fractional vacuum.
The chamber has now reached a pressure value higher than atmospheric pressure, causing the boiling point of the water to rise, resulting in hotter steam.
- Sterilisation step.
On reaching a temperature of 134 or 121 degrees centigrade, the material contained in the autoclave is left in contact with the steam for the time necessary to destroy all the vegetative forms of living spores.
- Steam draining and drying.
The steam is let out and the instruments are thermally and vacuum-dried.
- Balancing step.
Returns the pressure in the sterilisation chamber to the same level as atmospheric pressure.
- Traceability
Traceability makes it possible to uniquely identify key data relating to the load and its processing, using a label to be subsequently associated with the patient's medical record.
- Storage
Sterilised surgical instruments must be stored in a closed cabinet or drawer protected from humidity, aerosols and dust, and with visible expiration labels.
Sterility can be maintained up to maximum six months, depending on the weight of the bag.
Sterile or sterilised surgical instruments?
"Sterile" and "sterilised" are not synonyms:
- A sterile instrument has been subjected to an autoclave cycle, wrapped, dried, placed in an intact bag, stored under sterile conditions in a suitable environment until it is used.
- A sterilised instrument has been processed in an autoclave, but not wrapped or wrapped in a bag that is not airtight or is damaged or past its expiry date. At the time of use, the instrument is no longer sterile but simply decontaminated.
Sterilisation guidelines for surgical instruments
The sterilisation process is conditioned by four associated factors:
- pressure
- temperature
- humidity
- time
The sterilisation time of surgical instruments is inversely proportional to the temperature.
The steam pressure will cause an increase in temperature and a decrease in sterilisation time.
The steam used must always be saturated, i.e. with a liquid concentration not exceeding 3% without air in the condensable gases.
The most commonly used values for sterilisation are:
- 134 degrees centigrade for 4 minutes at 2.1 bar
- 121 degrees centigrade for 20 minutes at 1.1 bar
With this method you can sterilise all instruments except the heat sensitive ones.
Sterilisation in a saturated steam autoclave is a fast and effective process, economically sustainable, which does not imply any toxicity and respects the environment.
In conclusion we are quoting the criteria of the UNI EN 556-1:2002 standard:
“sterilisation must be performed with repeatable, standardisable, verifiable and documentable methods”.
Process traceability is achieved thanks to the microprocessor fitted to latest generation autoclaves, which allows the printing of cycle reports and labels for the bags in storage.
On some latest generation models it is also possible to automatically save the data relating to the cycles carried out directly to the Cloud. This allows to work around problems relating to the availability of data space inside the autoclave.
