Methods of sterilization and quality control
Sterilization is the process of destroying all types of microbial flora, including their spore forms, and viruses using physical or chemical effects. It is accepted to consider a medical product as sterile.
If the probability of its bioburden is equal to or less than 10 in degree -6. Medical products in contact with the patient's blood, in contact with the wound surface and in contact with the mucous membrane and may cause a violation of its integrity must be sterilized.
Sterilization is a complex process that requires the following requirements for its successful implementation:
- effective cleaning;
- suitable packaging materials;
- observance of the rules of packaging of medical products;
- compliance with the rules for loading the sterilizer with packages of medical products;
- adequate quality and quantity of sterilized material; appropriate operation of the equipment;
- compliance with the rules of storage, circulation and transportation of sterilized material.
The process of sterilization of medical instruments and products from the moment of the end of the operation to sterile storage or the next use includes the implementation of measures in a certain sequence.
All stages must be strictly followed to ensure sterility and a long life of the instruments.
Schematically, it can be represented as follows:
Put tools away after use;
Disinfection -> Mechanical cleaning of the instrument -> Check for damage -> Wash the instruments Drying -> Pack in sterilization packaging -> Sterilization -> Sterile storage/use. When using sterilization packaging (paper, foil or sterilization containers) instruments can be stored in a sterile form and later used from 24 hours to 6 months.
Several forms of sterilization organization are used in medical and preventive institutions: decentralized, centralized, carried out in CSO, and mixed.
Decentralized sterilization is more often used in outpatient dental practice (especially in private clinics).
Centralized sterilization is characteristic of district dental polyclinics and large private clinics.
Decentralized sterilization has a number of significant drawbacks that affect its effectiveness.
Pre-sterilization processing of products is most often performed manually, and at the same time, the quality of cleaning products is low. Control over compliance with sterilization technology, packaging rules, loading of products into sterilizers and the efficiency of equipment operation in conditions of decentralized sterilization is difficult. All this leads to a decrease in the quality of sterilization.
When using a centralized form of sterilization, it is possible to achieve higher sterilization results due to the improvement of existing and the introduction of the latest methods of sterilization (mechanization of washing instruments and medical products, facilitating the work of secondary medical personnel, etc.).
In the centralized sterilization department, there are: washing, disinfection, packaging, and a division for sterilization and separate storage of sterile items. The air temperature in all units should be from 18 ° C to 22 ° C, relative humidity - 35-70%, the direction of air flow - from clean to relatively polluted areas.
Sterilization methods:
Sterilization is carried out by physical methods: steam, air, glasperlene (in the environment of heated glass balls), radiation, using infrared radiation, and chemical methods: chemical solutions and gases.
In recent years, ozone and plasma sterilization have been used, installations based on ethylene oxide and formaldehyde vapors are used. The choice of method of sterilization of products depends on their resistance to methods of sterilization.
Sterilization quality control is one of the most important measures.
The physical method of controlling the operation of sterilizers consists in measuring such parameters as temperature, pressure and sterilization time. Any deviation from the standard sterilization modes is a signal to the operator about the probable failure of the equipment.
The chemical control method consists in recording changes in color or physical properties of indicators used to control exposure time and sterilization conditions. The most important method of quality control of sterilization is the biological method.
The Centers for Disease Control and Prevention recommend monitoring the operation of steam sterilizers in hospitals at least once a week. As biological indicators, spores of Bacillus stearothermophilus are used in air sterilizers, spores of Bacillus subtilus (biovar niger or globigii) are used in gas sterilizers. Spore biological control must be carried out every time the sterilizer is loaded with "critical" items. Critical instruments and vascular catheters should not be used until a negative spore test result is obtained.
Ideally, the storage area for sterile items should be located next to the sterilization area, and sterile products should be protected from dust, moisture, insects, parasites, temperature and humidity changes.
Sterile products must be laid out in such a way as to protect the packaging from damage, breakage, crushing and punctures. The "expiry date" is the time during which the products retain sterility. According to various data, the shelf life is measured from 2 days to an indefinite time, however, in most studies, the type of packaging material and storage conditions were not taken into account.
The loss of sterility depends on storage conditions and practically does not depend on time. To transport sterile instruments to the operating room and other departments of the hospital, it is necessary to provide an additional cover that protects against dust, which can be easily removed before entering the clean area.
All products undergo pre-sterilization cleaning before sterilization.
When sterilizing by physical methods (steam, air), products are usually sterilized packed in packaging materials approved in accordance with the established procedure for industrial production and use in Ukraine. With the steam method, sterilization boxes without filters and with a filter can be used. With the air method, as well as with steam and gas methods, sterilization of tools in a packaged form is allowed.
Steam method of sterilization
Medical products, parts of devices and apparatus made of corrosion-resistant metals, glass, surgical linen, dressing and suture material, rubber products (catheters, probes, tubes), latex, and plastics are sterilized by the steam method.
In the steam method, the sterilizing agent is water saturated steam under an excess pressure of 0.05 MPa (0.5 kgf / cm2) - 0.21 MPa (2.1 kgf / cm2) (1.1-2.0 bar) at a temperature of 110- 134 ° C. The sterilization process takes place in sterilizers (autoclaves).
The full cycle is from 5 to 180 minutes. Despite the fact that steam treatment is quite effective, it cannot always ensure sterilization of the instrument.
The reason for this is that air cavities in objects to be sterilized can act as thermal insulators, such as dental turbine tips. To solve this problem, autoclaves use the function of creating a preliminary vacuum in pulse mode.
The advantages of the method are a short cycle, the possibility of sterilization of heat-resistant products, the use of different types of packaging. The disadvantage is the high cost of the equipment. Modes and control of steam sterilization
Air method of sterilization
Sterilization with the air method is carried out with dry hot air at a temperature of 160 °, 180 ° and 200 ° C. Medical products, parts of devices and apparatus made of corrosion-resistant metals, glass marked 200 ° C, products made of silicone rubber are sterilized by the air method.
Before sterilization by the air method, the products undergo pre-sterilization cleaning and must be dried in a drying cabinet at a temperature of 85 ° C until visible moisture disappears. The full cycle takes up to 150 minutes.
The advantage of hot air sterilization compared to the steam method is the low cost of the equipment.
Disadvantages are: a long full sterilization cycle (at least 30 minutes), the danger of damaging tools with high temperatures, the impossibility of sterilizing fabrics and plastics, only one control parameter - temperature, high energy costs.
Glasperlen type of sterilization
glasperlen sterilization is carried out in sterilizers that use a sterilizing agent in which there is a medium of heated glass balls at an operating temperature of 190-330 ° C.
During sterilization, dry instruments are placed in the middle of heated glass granules to a depth of more than 15 mm. Only instruments whose size does not exceed 52 mm can be sterilized by this method, they must be completely immersed in the chamber for 20-180 s depending on the size.
After sterilization, the products are used immediately as intended. The high operating temperature and the impossibility of fully immersing the instruments in the sterilizing medium limit the possibility of sterilizing a wide range of medical products.
Sterilization by gas method
For the gas sterilization method, a mixture of ethylene oxide and methyl bromide in a weight ratio of 1: 2, 5, respectively (PRO), ethylene oxide, vapors of formaldehyde solution in ethyl alcohol, ozone is used.
Sterilization with a mixture of ABM and ethylene oxide is carried out at a temperature of at least 18 ° C, 35 ° C and 55 ° C, with vapors of a solution of formaldehyde in ethyl alcohol at a temperature of 80 ° C. Before gas sterilization, after pre-sterilization cleaning, the products are dried until visible moisture disappears.
Removal of moisture from product cavities is carried out using a centralized vacuum, and in its absence, using a water jet pump connected to the water supply.
When sterilizing ABM and ethylene oxide, air is removed to a pressure of 0.9 kgf/cm2. When using a portable device, after the end of sterilization, it is kept in a fume cupboard for 5 hours.
Ozone produced in an ozone sterilizer sterilizes products of simple configuration made of corrosion-resistant steels and alloys, in a packaged form at a temperature of no more than 40 ° C.
The sterilization cycle (entering the mode, sterilization, deactivation) is 90 minutes. After sterilization, the instruments are used as intended immediately without additional ventilation.
The period of preservation of sterility of products is 6 hours, subject to compliance with the rules of asepsis. When packed in a sterile two-layer cotton fabric, the term of sterility is 3 days, and when contained in a chamber with bactericidal irradiators - 7 days.
Infrared sterilization
intended for sterilization processing of metal medical instruments in dentistry, microsurgery, ophthalmology and other fields of medicine.
The high efficiency of the IR-sterilizing effect ensures complete destruction of all tested microorganisms, including such as: S. epidermidis, S. aureus, S. sarina flava, Citrobacter diversus, Str. pneumonia, Bacillus cereus.
Fast, within 30 seconds, access to the 200 ± 3 ° C mode, a short cycle of sterilization processing - from 1 to 10 minutes, depending on the selected mode, along with low energy consumption, incomparable in terms of fuel efficiency with any of the methods used to date sterilization
The IR sterilization sterilizer is easy to operate, does not require specially trained operators, and the method itself refers to environmentally friendly technologies.
Unlike steam, air or glasperlen sterilization, IR sterilization does not have an aggressive effect of the sterilizing agent (infrared radiation) on the cutting tool. Gamma rays are active agents of ionizing radiation.
LPU does not use ionizing radiation for disinfection. It is used for sterilization of single-use products during production in factory conditions.
Sterilization with chemical solutions
This method is used to sterilize products whose materials are not heat-resistant, and the use of other officially recommended methods is impossible.
The disadvantage of this method is that the products cannot be sterilized in the package, and after sterilization they must be washed with a sterile liquid (water or 0.9% sodium chloride solution), which, in case of violation of the rules of asepsis, can lead to secondary inoculation of sterilized products with microorganisms.
For chemical agents, use sterile containers made of glass, heat-resistant plastics that can withstand sterilization by the steam method, metals covered with enamel. The temperature of the solutions, except for special modes of application, should be at least 20 ° C for aldehyde-containing agents and at least 18 °
The chemical method of sterilization is quite widely used for processing "problem equipment", for example, for equipment with fiber optics, anesthetic equipment, pacemakers, and dental instruments.
Such modern sterilizing agents as glutaraldehyde, derivatives of orthophthalic and succinic acids, oxygen-containing compounds and derivatives of peracetic acid are used in the mode of express sterilization and "Classic sterilization".
Preparations obtained on their basis are considered promising - "Surfanios lemon fresh UA", "Aniozym DD1 UA", "Korzolex extra", "Eklin-Oxy", "Aniosept Aktiv", "Eklin-Nuk", "Steranios", their inequities , which is determined by the terms of use of working solutions
Removable products are sterilized in disassembled form. In order to avoid violation of the concentration of sterilization solutions, the products immersed in them must be dry.
The processing cycle is 240-300 minutes, which is a significant drawback of the method. In addition, the disadvantage is the high cost of disinfectants.
The advantage is that there is no special equipment. Washed sterile products after removal of liquid from channels and cavities are used immediately as intended or after packaging in a double-layer sterile cotton calico, placed in a sterile box lined with a sterile sheet for a period of no more than 3 days.
All work on sterilization of products is carried out in aseptic conditions in special rooms prepared as an operating unit (quartz-cevanie, general cleaning).
The staff uses sterile overalls, gloves, and glasses. Products are rinsed in 2-3 changes of sterile water, 5 minutes each.
Sterilization efficiency control
Sterilization effectiveness is controlled by physical, chemical and bacteriological methods.
Physical control methods include: measuring temperature, pressure and time of sterilization.
For decades, chemicals with a melting point close to the sterilization temperature have been used for chemical control. These substances were: benzoic acid - for steam sterilization; sucrose, hydroquinone and some others - to control air sterilization.
If there was a melting and a change in the color of the specified substances, then the result of sterilization was recognized as satisfactory.
Since the use of the above-mentioned indicators is not sufficiently reliable, chemical indicators, the color of which changes under the influence of a temperature adequate for a specific mode, for a certain time required for the implementation of this mode, are currently implemented in the practice of controlling thermal methods of sterilization.
The main parameters of sterilization - the temperature and duration of sterilization - are judged by the change in the color of the indicators.
Chemical indicators.
General requirements, in which chemical indicators are divided into six classes:
Class 1 includes external and internal process indicators, which are placed on the outer surface of packaging with medical products or inside tool sets and surgical linen. A change in the color of the indicator indicates that the package has been sterilized.
Class 2 includes indicators that do not control sterilization parameters, but are intended for use in special tests, for example, on the basis of such indicators, the efficiency of the vacuum pump and the presence of air in the steam sterilizer chamber are evaluated.
Class 3 includes indicators that determine one sterilization parameter, for example, the minimum temperature. However, they do not provide information about the time of exposure to temperature.
Class 4 includes multi-parameter indicators that change color under the influence of several sterilization parameters.
Class 5 includes integrating indicators that respond to all critical parameters of the sterilization method.
Indicators-emulators belong to the 6th class. The indicators are calibrated according to the parameters of the sterilization modes in which they are used. These indicators respond to all critical parameters of the sterilization method.
emulated indicators are the most modern. They clearly record the quality of sterilization with the correct ratio of all parameters - temperature, saturated steam, time.
If one of the critical parameters is not observed, the indicator does not work. All operations with indicators - extraction, evaluation of results - are carried out by the personnel who carry out sterilization.
Evaluation and accounting of the control results is carried out by evaluating the color changes of the initial state of the thermo-indicator label of each indicator, comparing it with the color label of the reference standard.
If the color of the final state of the thermal indicator label of all indicators corresponds to the color label of the comparison standard, this indicates compliance with the required values of the parameters of the sterilization modes in the sterilization chamber.
Differences in the intensity of the color depth of the thermo-indicator label of the indicators are allowed, due to the unevenness of the permissible temperature values in different zones of the sterilization chamber.
If the Thermoindicator label of at least one indicator completely or partially retains its color, easily differs from the color of the reference state, this indicates non-compliance with the required values of the parameters of the sterilization modes in the sterilization chamber.
Indicators and standards of comparison must match by batch numbers. It is forbidden to evaluate the results of sterilization control using indicators of different batches.
The conformity assessment of the change in color of the thermal indicator label in comparison with the Etalon is carried out under illumination of at least 215 lux, which corresponds to a matte incandescent lamp of 40 W, from a distance of no more than 25 cm.
Currently, bioassays are used to carry out bacteriological control, which have a dosed number of spores of the test culture.
The existing method allows you to evaluate the effectiveness of sterilization no earlier than after 48 hours, which does not allow you to use already sterilized products until the results of bacteriological control are obtained.
Biological indicator
It is a preparation of pathogenic spore-forming microorganisms with known high resistance to this type of sterilization process.
The task of biological indicators is to confirm the ability of the sterilization process to kill resistant microbial spores.
This is the most critical and reliable test of the sterilization process. Biological indicators are used as load control: if the result is positive (microbial growth), then this load cannot be used and all previous loads must be recalled until the last negative result.
To obtain a reliable biological response, only those biological indicators that meet the international standards EC 866 and ISO 11138/11135 should be used.
When using biological indicators, certain difficulties arise - the need for a microbiological laboratory, trained personnel, the duration of incubation is many times longer than the duration of sterilization, the need for quarantine (impossibility of use) of sterilized products until the results are obtained. Due to the above-mentioned difficulties in the application of the biological method in outpatient dental practice, a physical and chemical method of controlling the effectiveness of sterilization is usually used.
