A number of well-established and emerging sterilisation and disinfection products and systems are available for use on endoscopic equipment.
High-level disinfectants are chemicals that can act as sterilants if an increased exposure time is utilised. For a chemical to be used as a high-level disinfectant or a sterilant it must be registered as such with the Therapeutics Goods Administration (TGA).
High-level disinfectants for endoscope reprocessing need to have wide anti-bacterial properties together with the ability to kill relevant viruses including HIV, HBV and HCV. The properties of an ideal chemical sterilant or high-level disinfectant are listed in the table below.
Unfortunately the ideal high-level disinfectant does not exist as all products have limitations. Oxidising agents such as peracetic acid and chlorine based agents are generally better biocides than the alkylating agents but have a poorer materials compatability. Alkylating agents such as glutaraldehyde and formaldehyde are generally not as good a biocide as are the oxidising agents but have a better materials compatability.
As discussed in the Cleaning, Disinfection and Sterilisation section the ideal situation would be that flexible endoscopes, as semi-critical devices, should be heat sterilised. This is not possible because of their complexity and fragility and thus a chemical sterilisation process or high-level disinfection is deemed appropriate. Accessories that enter sterile sites must be sterile. This section will discuss agents that can be used for high-level disinfection or sterilisation of endoscopes and/or their accessories.
It is important that the manufacturers of endoscopes and reprocessors are consulted for results of compatibility studies as part of the process of choosing a product. Incompatibility may result in changes in appearance and function of an endoscope and may void the instruments warranty.
Age, dilution and organic stress affect the minimum effective concentration (MEC) of these agents and hence their MEC must be regularly tested to detect any changes. The disinfection or sterilisation process must also be validated.
Any sterilisation and disinfection process must be carried out in accordance with the current Australian standard AS 4187.
Glutaraldehyde is a saturated dialdehyde that has justifiably gained wide acceptance as a high-level disinfectant and chemical sterilant. The biocidal activity of glutaraldehyde is a consequence of its alkylation of sulfadryl, hydroxyl, carboxyl, and amino groups, which alters RNA, DNA and protein synthesis within microorganisms.
Glutaraldehyde has excellent biocidal activity, is active in the presence of organic matter and is non-corrosive to metals, rubbers and plastics. Olympus, Pentax and Fujinon list glutaraldehyde as compatible with their endoscopes. Glutaraldehyde can be used in manual and automated reprocessing protocols.
Glutaraldehyde products are marketed under a variety of brand names and are available in a variety of concentrations, with and without surfactants. For the high-level disinfection of endoscopes using a manual system, a 2% glutaraldehyde solution without surfactant is recommended.
Alkaline 2% glutaraldehyde preparations (e.g., Cidex) require 'activation' to raise the pH to 7.5 - 8.5 to make the solution sporocidal. The shelf life of activated solutions however is limited to 14 days.
Glycolated 2% glutaraldehyde solutions (e.g., Aidal plus) are stable for longer periods.
Biocidal data for glutaraldehyde products differs for the different formulations. The use of glutaraldehyde products for high-level disinfection should be in accordance with the product label. The label claims for the use of glutaraldehyde as a high-level disinfectant and a sterilant are determined by the TGA.
The major problem associated with glutaraldehyde is that it is a known respiratory and dermal irritant and sensitiser, and adverse health effects may occur in exposed workers. Consequently there are workplace health and safety requirements relating to its use. These are discussed in the Workplace Health and Safety module which is the next module.
Failure to rinse disinfected equipment thoroughly, thus leaving residual glutaraldehyde on the endoscope, has led to serious conditions including chemical colitis, pancreatitis and mucosal damage in patients.
Peracetic acid or peroxyacetic acid is an oxidising agent and functions by denaturing protein, disrupting cell-wall permeability and oxidising sulphydryl and sulphur bonds in proteins, enzymes and other metabolites. It has a rapid, broad-spectrum antimicrobial activity, is not readily inactivated by organic matter and is sporocidal even at low temperatures. This chemical can be corrosive to some metals but additives and pH modifications can reduce this effect. It is considered unstable particularly when diluted.
In Australia this biocide is used in a number of automated processors (Steris System 1®, Steris Reliance Endoscopic Reprocessing System, Medivator Advantage and the Soluscope 3CC-PAA). The Steris System 1 uses a liquid chemical process capable of sterilization. The sterilant, 35% peracetic acid, is diluted to 0.2% and operates at a minimum temperature of 50°C; requiring an exposure time of 12 minutes, with the complete processing cycle taking 25 - 30 minutes. Instruments are processed in an unwrapped condition and are wet when removed from the processor, therefore, they cannot be stored in a sterile state after processing. The Soluscope 3CC-PAA is a liquid chemical process approved for high level disinfection. The concentrated active ingredient is located in a 5 litre container in the machine. When the cycle reaches the disinfection stage, the system doses the concentrate with the buffer solution into the system to achieve a minimum concentration of 0.07%. The process occurs at 45°C with exposure time of the biocide of 5 minutes and the complete processing cycle of 15-22 minutes depending if a precleaning cycle is selected. The Medivator Advantage uses two separate chemicals which are mixed to create a single shot dose for each disinfection cycle.
Pentax, Olympus and Fujinon all list the Steris System as compatible with their endoscopes if used in accordance with the manufacturers instructions and with the validated connectors
The concentrate may cause irritation and is corrosive and, although the system is contained, must be handled with the appropriate PPE according to the MSDS. The ionic concentration of the buffer is monitored instead of the active compound.
Ortho-Phthalaldehyde (OPA) is an alkylating agent which contains 0.55% 1,2-benzenedicarboxaldehyde. It has shown superior mycobactericidal activity compared to glutaraldehyde with less contact time required, other advantages include excellent stability over a wide pH range of 3-9, and no activation requirement. There is limited 'in use' data available about this product.
The high-level disinfection claim for OPA is 10 minutes at 20°C if soaking in a manual system. Where OPA is used within an automated system the parameters of 5 minutes at 25°C should be attained. Check with the manufacturers of automated reprocessors for specific compatibility statements.
Pentax, Olympus and Fujinon list OPA as a product compatible with their flexible endoscopes. This chemical stains protein so rigorous rinsing is required to remove the OPA from the surfaces of the endoscopes.
OPA is a potential respiratory and dermal irritant and there have been problems with prolonged or repeated contact. A product safety alert cautions against use for cystoscopes which are to be used on patients with bladder carcinoma. Although it is not classed as a hazardous chemical it would be prudent to handle it with the same precautions as glutaraldehyde.
See the discussions in the Workplace Health and Safety module.
Click here for more information on Automatic Flexible Endoscope Reprocesors.
Sterilisation can be achieved by means of heat or ionising radiation as well as chemicals.
Any sterilisation process requires verification in terms of proof of process. This is discussed in the Quality Assurance module.
Steam is the most widely used and most effective agent for sterilisation. In steam sterilisation the combination of heat and moisture, maintained at a pre-set temperature-pressure-time relationship in a steriliser coagulates cell protein, efficiently killing the microorganisms. The latent heat available is responsible for the fast destructive power that steam under pressure offers and it is also a very economical and non-toxic process.
Steam under pressure sterilisation is used for reusable accessory endoscopic equipment that is used in critical sites and therefore is required to be sterile. It is also used for ancillary endoscopy equipment such as the water bottle system. The basic principle is that if an item can be reprocessed by steam sterilization that procedure should be used. Liquid processes carry a much lower level of sterility assurance.
Most endoscopic equipment is not suitable to be exposed to either the pressure or the temperatures required in this process. Verification should be sought from the manufacturer that an item is capable of withstanding steam under pressure sterilization
There are a number of different types of steam under pressure sterilisers such as, pre-vacuum and downward displacement sterilisers. They should be used according to the manufacturer's instructions as well as the health care facilities guidelines.
Ethylene oxide (ETO) is a gaseous chemical used to sterilize heat and moisture sensitive items that cannot withstand temperatures greater than 60°C.
ETO must be used in accordance with the relevant workplace health and safety legislation in each state. National and State recommendations and guidelines for ETO use should also be followed.
Very few hospitals have an ETO steriliser. The gas is dangerous and should only be used where suitable equipment, strict environmental controls and specially trained staff are available. Biological indicators are required for routine monitoring.
Whilst low pressure or sub-atmospheric ETO sterilisers are capable of sterilising some flexible endoscopes it will be ineffective if the items are not properly cleaned prior to sterilisation. The gas may not penetrate very fine channels thus there is much equipment that cannot be sterilised with this process.
When this process is used an ETO venting cap must be fitted in accordance with the manufacturer's instructions and the instrument suitably packaged or contained.
This process is unlikely to be suitable if a quick turn around time is required because of the lengthy periods (1-7 days) required for processing, the incubation period for biological indicators and aeration to remove residual gas.
Plasma is the fourth state of matter, distinguished from solid, liquid and gas. Gas plasma is a highly excited body of gas produced by the application of energy to a gas under vacuum, making ions and molecules within the plasma collide to produce free radicals. These are involved in alkylation of the protein in the microbial cell.
The Sterrad® automated sterilisation system uses low-temperature hydrogen peroxide gas plasma to achieve low-temperature, low-moisture sterilisation, usually within a one-hour automated cycle. Special adapters (H202 boosters) are required for use with devices with lumens to ensure the sterilant gains access to these areas. The system requires the use of non-woven (non-cellulose) polypropylene wraps or packaging.
Instruments with very long narrow lumens, and those closed at one end, are unsuitable for sterilisation using hydrogen peroxide gas plasma. Some shorter flexible endoscopes and accessories have been validated for sterilisation with this system.