Focus sui processi di sterilizzazione in autoclave
Autoclave packaging for efficient sterilization
While steam and pressure are vital factors in the efficiency of the sterilization process, the packaging of the items is pivotal to achieve a cost-efficient autoclave cycle. Cristina Masciola, communications manager at AM Instruments, explains
One of the most delicate phases in pharmaceutical production processes is autoclave sterilization. However, the very concept of sterility is challenging. Arguably, to say that an object or environment is sterile doesn’t mean the total absence of contamination, only that it contains the lowest concentration of possible contaminants. Consequently, such a condition needs to be addressed.
One of the most delicate phases in pharmaceutical production processes is autoclave sterilization. However, the very concept of sterility presents an anomaly. In fact, to say that an object or environment is sterile does not indicate the total absence of contamination, only that it contains the lowest concentration of possible contaminants. Therefore, the situation needs to be addressed.
SAL (Sterility Assurance Level) is used to express the probability of bacterial survival and therefore defines an area as sterile where 1 out of 10,000,000 units is contaminated (the bacterial count equals 10 -6).
In the past, sterilization was defined as a process through which all possible life forms, including spores, were completely destroyed by passing an object through an autoclave that would allow the absence of germ proliferation. Subsequently, it became evident that passage through an autoclave does not ensure sterility per se: a cycle in an autoclave is a process that must be considered in its entirety, from the preparation of the materials to their storage. None of these phases can be underestimated for the purpose of a successful sterilization cycle.
The autoclave consists of a steel container, equipped with a door that can be hermetically sealed from the outside. Through special ducts, the water vapor coming from a boiler is pushed into the autoclave by a pump. The air initially contained in the autoclave is let out until only steam under pressure remains inside it. The pressure that is reached inside is about 6.9 · 10-3 kPa (0.7 atm) higher than normal, which corresponds to a water vapor temperature of just over 115°C. It should be kept in mind that all forms of bacteria, molds, and yeasts die after only a few minutes of exposure to 100°C and that the most resistant spores (i.e. those of the tetanus bacillus) die at 115°C in 15′. Normally, good practice dictates that sterilization is continued for 20 minutes. This guarantees that all pathogenic and non-pathological forms of any kind are dead and therefore the material inside the autoclave is perfectly sterile.
To effectively combat bacteria and viruses that form spores, autoclaves require that:
- the sterilizing agent reaches all surfaces of the object to be sterilized. Some materials have a smooth, well-exposed structure, while others are much more articulated and therefore present more management problems.
- the steam is in direct contact with the sterilized material. This involves particular care during the loading phase of the autoclave.
- a vacuum is created to move all the air initially present in the autoclave and then replace it with steam
- a well-designed control scheme for steam evacuation and cooling is implemented so that the load does not deteriorate
The efficiency of the sterilization process depends on two main factors: steam and pressure.
Steam and pressure ensure that enough heat is transferred into the organisms to kill them. A series of negative pressure pulses are used to remove all possible air pockets, while steam penetration is maximized by applying a succession of positive pulses.
The relationship between temperature and pressure is generally the following:
We want to conclude this part relating to the specifications of the machine considering the type of materials inserted and the relative pressure loops.
In general, we could consider a subdivision as follows:
|MATERIAL||TEMP.C°||TIME (MINUTES)||PRESSURE (BAR)|
|Textiles, instruments and packaged glassworks
|Tools and glassware not
|Material in rubber or autoclavable plastic||121||15||1.1|
We have developed a descriptive but essential framework to understand the importance of the phases prior and subsequent to the sterilization cycle in an autoclave. In fact, what has been stated regarding the main characteristics of the machine is nullified if the risks connected to the preparation of the material to be sterilized are not considered from the time of loading up to the final storage.
Let’s start with the preparation of the material.
The microbial charge present on an object (bioburden) can be mild, medium or severe. For this reason, it must be effectively removed through decontamination and washing, both of which are essential preventive actions of the sterilization process.
The subsequent packaging phase has specific purposes such as:
- to allow the removal of air and, therefore, the penetration and contact of the sterilizing agents
with the surface of the object to be treated;
- to reduce the risk of contamination of the sterilized material when the sterile package is open;
- to preserve the sterility of the treated material until it is used;
- to be free of toxicity
- to be practical, convenient and economical
“Good” packaging depends on several factors:
- material used
- packaging methods
- structure of the object to be packaged
Medical paper is the most commonly used but also the most at-risk type of material. In fact, medical paper requires first and foremost a high level of operation and handling with possible damage to the equipment; the coverage is irregular (some parts are covered by a single layer, others by two) causing an irregularity in the passage of steam; and it is often difficult to remove. A high risk of fiber release combined with the possibility of tears and damage is added to the list of risks associated with the use of medical paper. Finally, a very important factor to consider in a production cycle is time; the operational time for packaging is certainly high.
An effective and safe packaging method is one that meets certain requirements, such as:
- designed to offer total security and resistance
- customizable and easy to use
- not influenced by autoclave sterilization processes
- resistant to tears and perforations
- easy to apply and remove
- minimal handling
- no taping if possible
- low particle release
- excellent microbiological barrier
- uniform penetration of steam through the surface
With the above in mind, Tyvek® material packaging systems provide the solution. They are designed with the aim of making the preventive preparation operation not only safe for the autoclave cycles of the materials, but also to minimize the operating times required by the cycle.
Unlike medical paper, Tyvek® material generates very few airborne particles when opened or manipulated. This low linting release property minimizes the risk of introducing particulate matter into a clean environment. A further advantage of using Tyvek® material for sterilizable steam bags is that, unlike medical paper, Tyvek® maintains its dimensional stability and high-quality visual appearance after steam sterilization. Even in the most severe conditions in highly contaminated environments, it is highly resistant to the penetration of bacterial spores and other contaminating microorganisms.
Packaging with medical paper
Packaging with Pharmaclean®
Particle and bacteriological tests clearly show that it performs better than other commercially available porous packaging materials, including medical paper.
Once the packaging has been carried out, autoclave loading represents an equally important step for the success of the sterilization cycle. It must be performed in such a way that the steam can circulate freely and penetrate each package:
- the autoclave load must be evenly distributed and must not touch the internal walls
- the items to be sterilized must be arranged so that each surface is
exposed to the sterilizing agent for the expected temperature and time
- special tools, such as containers, pipes, etc., must be arranged with the opening facing
downwards to prevent condensation and the formation of air bubbles.
After the cycle, exactly as for the preventive phase, it is obviously necessary to follow other procedures that ensure sterility is perfectly maintained and that require the cycle to be repeated in case of damaged packages or contact with wet surfaces, among other things.
Pharmaclean® by AM Instruments, the line launched by the Italian company which has been at the forefront of contamination control for almost thirty years, fully meets the regulatory requirements, through the use of Tyvek® material packaging and sterilization systems made in standard and custom-made formats that allow the operator minimum manipulation in total safety. The systems are located in A / C grade cleanrooms.
The Pharmaclean® area and production processes are designed and managed in order to minimize the risk of microbiological and particulate contamination. Microbiological checks are carried out in accordance with Annex 1, and particle checks are performed in accordance with ISO 14644.
- Structures, equipment and processes are qualified based on our Quality Management System and all operational phases are tracked in dedicated procedures or instructions
- Qualified personnel with adequate skills and continuous training
- A contamination control program defined by risk assessment related to structural and process characteristics
The QC laboratory Dedicated to Pharmaclean® production support:
- Analysis of the release of incoming raw materials
- Process controls on the finished product
- Monitoring of particle and microbiological contamination
- Qualification of analytical methods dedicated to custom repackaging processes