STERILISATION

STERILISATION

sterilizzazione

Instruments that have been in touch with a patient have to be correctly sterilized. This is a process made of a sequence of phases:

 

  1. Decontamination
  2. Cleaning
  3. Rinsing
  4. Packaging
  5. Sterilisation

DECONTAMINATION

The first phase of a correct sterilisation is when all the instruments are immersed in a container, in an appropriate chemical solutions. The aim is to kill all potential pathogens. The time that the sterilising solution has to remain in contact with the instruments depends on the solution used and it is appropriate to follow the instructions indicated by the producer.

CLEANING

Once the decontamination is done, is important to follow the procedure of cleaning in order to remove the remaining of organic/inorganic particles; this, in fact, reduces microbial contamination. Instruments cleaning may be performed manually or mechanically.
Manual cleaning is carried out when no automated devices are available or in case of special characteristics of the material. It is used a liquid cleaner containing tension-active compounds or enzymatic/multi-enzymatic cleaners. The instruments will be left for at least 15minutes in a container full of liquid and then brushed to remove organic residuals.
Another method of cleaning is the use of ultrasonic container. This method is based on the principle of physics called “ultrasonic cavitation”. Ultrasonic waves create gas bubbles that implode and therefor energy of shockwaves is released. The results constitute of a process of microbrushing and cleaning effect produced by the chemical substances in the container.

RINSING AND DRYING

After mechanical or manual cleaning, it is important to rinse the instruments in water and dry them with a paper towel.

PACKAGING

In this phase self-sealing paper and polypropylene envelopes or sterilisation rolls of different dimensions for various instruments length have to be used.
Self-sealing envelopes are more convenient because once the instrument is introduced in the envelope there is just a protective film to remove and the envelope is sealed.
The roll has to be cut at the instrument length and then heat-sealed.

STEAM STERILISATION

Steam sterilisation is the method most used in a medical environment because it is the most safe, fast, economic and ecologic. If the steam is combined with pressure, temperatures over 100°C may be reached. In fact, this method represents a combination of 3 factors: pressure, temperature and time. The temperature increases with the pressure of the steam. A typical device that uses steam is the autoclave. It contains a pressure chamber resistant to high pressures. According to the European laws each autoclave, before use, has to be submitted to control test cycles and also to routine control.

The steam sterilisation cycle is made of three phases:

  1. Heating
  2. Sterilisation
  3. Drying

During the first phase the autoclave makes fractionated vacuum in order to completely remove the air in the chamber. Then it starts to inject steam until it reaches a certain temperature (121°C, 134°C).
Once the temperature is reached, it follows a phase in which a correct sterilisation is occurring.
During the last phase the autoclave creates one more time the vacuum, eliminating the steam, in order to start the drying.

STERILISATION WITH PERACETIC ACID SOLUTIONS

This method, the so-called “cold sterilisation” is the one in which the instruments are immersed in a 2% peracetic acid solution. When the peracetic acid is dissolved in water it dissociates in hydrogen peroxide and acetic acid and thus becomes a powerful oxidant. This acid is able to deactivate a large variety of pathogen microorganism, virus and fungal spores.
For a correct sterilisation is important to follow some precise parameters:

  • the sterilisation agent concentration
  • the time of contact
  • the temperature of the solution
  • the pH of the solution

Temperature and pH play a fundamental role in the liquid preparation and the sterilisation is performed at 35°C and pH 7. At a temperature of 15°C and pH 7 it is necessary five times the standard equivalent of peracetic acid to deactivate the pathogens. Once sterilised, the instruments are packed and ready to be used.