Sterilization is the removal of all microorganisms (including spores) on an object by physical or chemical methods to achieve a sterile level, so as to reduce the occurrence of infection and the spread of disease caused by the use of medical devices.
Sterility refers to the probability of survival of a single microorganism after sterilization, also known as sterility assurance level (SAL), usually expressed as 10-n. Currently, the consensus is that SAL10-6 is sterile.
Common sterilization methods include: high pressure steam sterilization, hydrogen peroxide plasma sterilization, ethylene oxide sterilization, ionizing radiation sterilization, and dry heat sterilization.
Comparison of sterilization methods, principles, applications, advantages and disadvantages.
1. High pressure steam sterilization
Principle: Kill microorganisms mainly by irreversibly coagulating and denaturing enzymes and proteins in microorganisms.
Application: Mainly used to treat water, pharmaceuticals, regulated medical waste and non-porous items whose surfaces are directly exposed to steam. For perforated loads and instruments, the typical sterilization temperature and time are 132-135°C for 3-4 minutes. Commonly used sterilization temperatures are 121°C and 132°C.
Advantages: non-toxic and environmentally friendly, the process is easy to control and monitor, the sterilization is fast and effective, the sterilization process is minimally affected by organic or inorganic contamination, the sterilization cycle time is short, and it can effectively penetrate the instrument package and lumen-type instruments.
Disadvantages: damage to heat-sensitive instruments, repeated sterilization exposure will damage precision surgical instruments, and may cause instrument rust due to wet packs,potential scalding risk.2. Hydrogen peroxide plasma sterilization
Principle: Hydrogen peroxide plasma has high oxidative activity and kills microorganisms by destroying cellular proteins, enzymes and nucleic acids.
Application: Used for sterilization of medical supplies which are instable to heat and moisture.
Advantages: safe and environmentally friendly, no toxic residues, sterilization cycle of 28-75 minutes, no need for analysis, suitable for sterilization of heat and moisture sensitive items, easy to operate, install and monitor, and compatible with most instruments.
Disadvantages: Not suitable for paper fibers, cotton and linen, liquid items, the size of the sterilization cavity is small (50 ~ 270 L), not suitable for endoscopy or instruments with slender lumen, need to use synthetic packaging (such as polypropylene packaging or polyolefin tube bags, etc.), hydrogen peroxide may be toxic at doses higher than 1 ppm.
3. Ethylene oxide sterilization
Principle: Ethylene oxide induces cell death by alkylating proteins, DNA, and RNA, irreversibly preventing normal cell metabolism and replication.
Application: used for high-risk items that are not resistant to moisture and heat.
Advantages: It can sterilize heat-sensitive and moisture-sensitive medical equipment without harmful effects on its materials, can effectively penetrate packaging materials and lumen-type devices, single-dose box and negative pressure operation, reduce the risk of gas leakage, easy to use and monitoring, compatible with most instruments.
Disadvantages: high cost, potential harm to patients and medical staff. It must be analyzed for a long time to remove the residual ethylene oxide gas. The sterilizer is small in size (110-250L), toxic, carcinogenic and flammable. The tank must be stored in an explosion-proof storage cabinet, which requires a long sterilization cycle and analysis time.
4. Ionizing radiation sterilization
Principle: The γ-ray emitted by the radioisotope cobalt 60 is used as an effective sterilization factor. The γ-ray can induce cells to generate free radicals, destroy normal metabolism, and then lead to the inactivation of microorganisms.
Application: Low temperature sterilization applied to many medical products (such as tissue transplantation, pharmaceuticals, medical devices).
Advantages: It can be carried out at room temperature without special requirements for the temperature environment, the sterilization is uniform and thorough, the speed is fast, and it can be continuously operated. Suitable for large-scale sterilization.Disadvantages: high cost of sterilization, some products may change their properties after radiation, pay attention to safety protection issues.
5. Dry heat sterilization
Principle: Bacterial death is caused by high temperature oxidation of cellular components.
Application: For those materials that are not resistant to damp heat or cannot be penetrated by damp heat (eg powders, petroleum products, sharp utensils). The most common times and temperatures are 170 °C and 60 min, 160 °C and 120 min, and 150 °C and 150 min.
Advantages: non-toxic, environmentally friendly, dry heat cabinets are easy to install, relatively low operating costs, can penetrate materials, non-corrosive to metals and sharps, etc.
Disadvantages: The speed of sterilization heat penetration and microbial killing is slow, and sterilization is time-consuming. High temperatures are not suitable for most materials.In addition to the above sterilization methods, medical/pharmaceutical sterilization also involves other sterilization techniques, such as peracetic acid sterilization, ozone sterilization, ultraviolet irradiation sterilization, microwave sterilization, filtration sterilization, etc.