Choosing the right sterilizer

What are the different sterilization procedures?
What are the different classes of autoclaves?
When are sterilizers used?

Choosing the right sterilizer

Sterilization is the implementation of a set of methods and means to eliminate all living microorganisms, of any nature and in any form whatsoever, on a perfectly cleaned object. This process is carried out using a sterilizer. It is necessary in order to prevent the contamination of patients and caregivers. In order for a medical device that has undergone terminal sterilization to be considered “sterile” the theoretical probability that a viable microorganism is present on the device must be almost zero.

What are the different sterilization procedures?

There are many sterilization procedures that are more or less suitable depending on the field of application and the equipment to be sterilized. We can name four main ones: by heat, by gas, by plasma phase and by irradiation.

  • Sterilization by heat:
    Steam/wet heat:this procedure is carried out in a sealed enclosure inside which pressurized steam is injected. A steam sterilizer is also called an autoclave. This is the most common method used in healthcare facilities for all heat-resistant medical devices. It is reliable, inexpensive and non-polluting.
    By dry heat: in this case sterilization is carried out using hot, dry air, without increasing the pressure. The air temperature inside the sterilizer is increased, much like in an oven, except that there is no way for air to enter or escape. This process is not used as frequently today as bacteria can sporulate in dry heat. The high temperatures (180°C for 30 minutes or 160°C for two hours) can also damage the equipment.
  • Gas sterilization:
    With ethylene oxide:ethylene oxide is an alkylating agent that damages the DNA of microorganisms, preventing them from reproducing. Its sterilizing power is effective at low temperatures; it is therefore suitable for materials sensitive to steam and heat such as complex assembled devices, catheters, stents, certain electronic equipment, wound dressings, etc.
    Formaldehyde: the bactericidal action of this agent is identical to that of ethylene oxide. Formaldehyde even offers certain advantages over ethylene oxide, such as the absence of toxic residues and the absence of explosion risks.
  • Plasma phase sterilization: in this process hydrogen peroxide is used, excited by an electromagnetic field. Oxygen free radicals which have a highly sterilizing power are then formed. This type of sterilization is performed at a low temperature and is therefore suitable for heat-sensitive materials such as plastic or certain optical components (fiberscopes, etc.). This process is relatively easy to implement and does not require large installations.
  • Sterilization by irradiation: this is mainly used in industrial environments. It can be:
    UV: this process is based on the sensitivity of microorganisms to exposure to low ultraviolet wavelengths. The main applications of this procedure are the preparation of sterile work surfaces in research laboratories, food preservation and air or water purification.
    Infrared: through their absorption in the product, infrared rays cause heating to a depth with is limited according to their wavelength. The electromagnetic wave is usually generated by a magnetron. The technique of infrared heat sterilization is used in the food industry for the pasteurization of basic products only contaminated on the surface (grains, dried fruits, etc.) or cooked products that are packaged then pasteurized (pizzas, pastries, etc.).

What are the different classes of autoclaves?

The classification system takes into account the volume of the sterilization chamber.

  • With a volume less than 60 litres: these are small steam sterilizers. According to the EN 13060 standard, there are three classes of autoclaves:
  • Class B autoclaves: these are the only true sterilizers in the strict sense of the word. They carry out a cycle including pre-treatment with alternating vacuum and steam injections, a set sterilization phase and a vacuum drying phase. This class of autoclaves is the only one recommended by the EN 13060 standard for the sterilization of medical devices.
  • Class N autoclaves: these are actually steam disinfectors, used for the treatment of unpackaged devices.
  • Class S autoclaves: this is a non-specific class whose indications are defined by the manufacturer.
  • With a volume over 60 liters: you will need to take into account the EN 285 standard for large sterilizers.

What types of products can be sterilized?

Several types of products can be sterilized. Depending on the different sterilization procedures and temperatures, you can sterilize:

  • Solid products: they can be wrapped or unwrapped. There will be different cycles depending on whether you are sterilizing glass, metal, plastic, etc.
  • Liquid products: these are liquid products presented in containers, for example. Some sterilization processes cannot be used for liquid products such as ethylene oxide sterilization. Sterilization of liquids is a complicated task which can take a long time. It is important to know whether the liquids to be sterilized can reach the desired sterilization temperature of 121°C.
  • Porous products: these include textiles, rubber, etc.

When is it necessary to use a sterilizer?

Before installing a sterilizer and ensuring it will be used effectively, three main points must be considered: the organization, technical installations and staff training on the premises.

  • The organization of the premises:
    Hygiene: the premises must allow for compliance with procedures for hygiene, staff dress code and handwashing.
    Layout: arrangement and circulation procedures must prevent any risk of confusion between sterilized and non-sterilized medical devices.
    Surfaces: exposed surfaces must be smooth, impermeable, free of cracks and recesses to reduce the accumulation and release of particles and microorganisms.
    Maintenance: the premises must allow for the repeated use of cleaning and disinfection products.
    Intrusion: the premises must be equipped with a system to prevent the intrusion of animals (insects, rodents, etc.).
  • Technical installations:
    Air supply: the air supply must meet the current standards and have an air treatment system with the appropriate filters. It should be noted that the air pressure in the conditioning area must be higher than in other sectors.
    Water supply: the water supply must provide drinking quality water. The quality must be regularly assessed and monitored.
  • Staff training:
    Skill level: the quality of the preparation of medical devices depends very much on the competence, training and behavior of the personnel involved in these operations. Initial and continuous training is required for sterilization, using autoclaves, hygiene and safety, etc.
    Staff hygiene: each member of staff must report to management any infection he or she is infected with and that is likely to constitute a risk of contamination.
    Protection: protecting staff members against accidental contamination or injury is essential. It is absolutely necessary to respect the dress code procedures and rules for moving in the space.

What are the different steps of sterilization?

When medical devices have been used and require sterilization, they must go through a series of six steps:

  • Pre-disinfection: this must be carried out as soon as possible after the equipment has been used by completely immersing the instruments in a detergent and disinfectant solution. This reduces the population of microorganisms and therefore facilitates the subsequent cleaning of the instruments, while preventing environmental contamination.
  • Cleaning (or washing): it includes a mechanical action (to remove dirt by spraying and rubbing), a chemical action (to make dirt soluble with a detergent) and a thermal action (to speed up the cleaning and drying process).
  • Packaging: medical devices must be packaged before they pass through the sterilizer.
    Sterilization: it depends on the sterilization process you choose.
  • Verification: verification is carried out before, during and after sterilization.
  • Storage and availability: the packaging must include information to trace the sterilization process and expiry date. Today, the use of barcodes facilitates stock management and the expiry of the sterilization of reusable medical devices.