Sterilisation is required for various industries typically health care, laboratory, pharmaceutical and food processing industries. The most common and proven method used for sterilisation is sterilisation by pressurised high temperature steam in a pressure chamber or vessel for a prescribed period of time. Pressurised high temperature steam within a stainless steel pressure chamber is the preferred method for sterilisation of laboratory equipment and in the industrial manufacturing and healthcare sectors.
Various types of sterilisation pressure vessels and autoclave chambers are historically utilised to sterilise such objects, items or products (hereinafter “items”). In all instances the sterilant must make contact with the surface of the items for each item to be sterilised in order to enable sterilisation to occur.
For moist heat sterilisation using steam as the sterilant, it is essential that all surfaces of the items requiring sterilisation are subjected to saturated steam at a predetermined temperature and pressure for a predetermined period of time. Proper steam penetration requires adequate air removal.
Steam is the most widely used agent for sterilisation. In steam sterilisation, the combination of heat and moisture, maintained at a pre-set temperature-pressure-time relationship, coagulates cell protein, efficiently killing the microorganisms. Its economy and lack of toxicity gives steam an advantage over other sterilisation methods. The latent heat available is responsible for the fast destructive power that steam-under-pressure offers. There can be significant variation in steam quality and in order for steam to be effective it should have a dryness fraction of 97% and above.
Each of the multiple or variable types of steam sterilisers are designed to achieve specific sterilisation parameters and all cycles must be validated so that the cycle time and temperature shall reflect the load and packaging material being processed.
At the end of a correct sterilisation process, it is extrapolated that items inside the sterilisation chamber have reached an acceptable probability of sterility. The challenge to end users and steriliser manufacturers has been the variety of loads and varied manner of loading both in respect of how and what items are loaded and positioned in the chamber and how the load may be packaged. The load therefore has a direct impact on the relative efficacy of air removal from the chamber and the efficacy of the steam on the load and addressing and resolving all these variables is still a matter under debate.
In the medical environment, it is necessary that all medical items (equipment and materials) utilised for the treatment of patients are inherently safe for use so that the chance of spreading diseases is kept as low as possible. Hospital acquired infection is clearly the last thing either a patient or the hospital wants.
The challenge therefore is that a steriliser operator must minimise risk and make sure that the steriliser and sterilisation cycle selected for use is suitable for the intended purpose. Sterilisation is a controlled and monitored action and due to these complexities and the requirement to achieve the desired Sterility Assurance Level, international standards have been published; typically ISO 17665 focussing on the effective validation of the sterilisation of loads in a consistent, reproducible and recordable manner and ISO 14937 focussing on the general requirements for characterisation of a sterilisation agent and the development, validation and routine control of a sterilisation process.
An unavoidable problem that faces sterilisation practitioners is that the air in the room where the steriliser is installed contains airborne particles, which may carry microorganisms. Accordingly, when the sterile load is taken out of the steriliser, it may be contaminated again. Additionally sterile goods may be stored for quite some time before they are used. Moreover, they are transported through the hospital to the place they are to be used. It thus is probable that terminally sterile loads/items will become re-contaminated by the time they are used.
Consequently the items must be put in packaging to prevent recontamination after sterilisation. To minimise recontamination and augment the logistics and materials handling expediency of the sterilisation process, the item(s) are usually pre-packaged. The packaging heretofore typically include a fabric barrier typically, muslin wraps, various paper wraps and non-woven wraps, or alternatively laminated film pouches or sterilisation containers. The wraps are typically secured by autoclavable tape which may become detached during processing or in the handling of a package leading to rejection of the package. An important feature of fabric is its “breathability” or the ability of the fabric construction to allow the passage of air and water vapour i.e. steam. Current practices where breathable packaging is required to allow the passage of the sterilant (water vapour/steam) in and out of the package during the sterilisation process places huge demands on the breathable packaging at the conclusion of the sterilisation process to then act as a viral and liquid barrier to ensure impervious protection of the terminally sterile load. The sterilised package should be constructed so that it may be easily opened without the packaging contaminating the contents.
Traditional sterilisation cycles may require up to 20 minutes of air-removal from the chamber and packages and pre-heating of the load(s). Then sterilant is introduced until the correct sterilisation parameters of pressure and temperature have been established; to commence the sterilisation time duration (typically 3.5-5 minutes @ 134 degrees Celsius of steam penetration to facilitate sterilisation). Finally 20-40 minutes of vacuum drying to remove the condensate from the chamber and packages. This results in relatively long sterilisation cycles with limited flexibility.
Sterile services technicians must have an understanding of how to properly select and apply the correct wrap(s) for the sterilisation method chosen. Technicians are also responsible for quality assurance issues. They must assemble each package with care, being observant not to tear or damage the wrap.
Each package is uniquely organised, depending upon content, to promote the sterilisation process. Special attention must also be given to how the steriliser is loaded. After sterilisation the breathable packaging should provide an effective microbial barrier for immediate use of the sterile items or facilitate a shelf life.
It is essential that a packaging system with its content meet the requirements in terms of sterility maintenance and protection of its contents. That is why any packaging should be validated in combination with the actual load and the sterilisation process used.
It is clear to those skilled in the art of sterilisation of an item(s) in a consistent, reproducible and recordable manner, that this goal is made virtually impossible due to the multiple variables faced by sterilisation practitioners daily predominantly as a result of current technology and processes available to sterilisation practitioners.
The applicants prior application published as WO2007/055595 discloses a sterilisation method and apparatus in which items to be sterilised may be sterilised within a plastic bag whilst the exterior of the sterilisation bag is maintained at atmospheric pressure. Whilst effective, maintaining the exterior of the sterilisation bag at atmospheric pressure puts mechanical demands upon the sterilisation bag as it is evacuated and pressurised and may not optimise the flow of fluid into, within and out of the bag. The disclosure of this application is hereby incorporated by reference.
It is the object of the invention to provide an improved sterilisation method and sterilisation services apparatus or to at least provide the public with a useful choice.