Types of Methods:

1. Chemicals: Ethylene Oxide
2. Gas-plasma of hydrogen peroxide
3. Physical: Heat Radiation
4. Filtration
5. Sterilizing agents and disinfectants

 Chemical Methods

These methods cause the loss of viability of microorganisms.

Ethylene Oxide: It is an alkalizing agent that binds to labile hydrogen compounds such as those with carboxyl groups, amino, hydroxyl, etc. It is used in gas sterilization, usually in the pharmaceutical industry and destroys all microorganisms including viruses. Used to sterilize heat sensitive materials such as disposable (rubber, plastic, paper, etc..), Electronic equipment, cardio pump, metal, etc.. It is very dangerous to be highly flammable and explosive, and also carcinogenic.

Glutaraldehyde: Is to prepare a 2% alkaline solution and immerse the material to sterilize 20 to 30 minutes, and then a rinse of 10 minutes. This method has the advantage of being fast and being the only effective cold sterilant. You can sterilize plastic, rubber, glass, metal, etc.

Formaldehyde: Using Para formaldehyde tablets, which can be arranged in the bottom of a box wrapped in gauze or cotton, which can then be exposed to heat for a quick sterilization (action of formaldehyde gas). They can also be used in stoves Formaldehyde, which are boxes with false bottoms, where the tablets are placed and heated to 60 ° C and can sterilize materials, latex, rubber, plastics, etc..

Pills sterilized formalin at room temperature in 36 hours.

Gas-plasma sterilization by hydrogen peroxide: It sterilization process at low temperature which consists in transmitting hydrogen peroxide plasma phase (state between liquid and gas), which performs the biocidal action.

Advantages:

1. Leaves no toxic residue.
2. It turns into water and oxygen at the end of the process.
3. The material does not need aeration.
4. The sterilization cycle lasts between 54 and 75 minutes.

Disadvantages:

1. You can not sterilize objects containing cellulose, cotton, liquid, moisture, wood or instruments with long narrow lumens.
2. Sterilization is the most expensive method among those described.

Physical methods

Heat: Using this method and its effectiveness depends on two factors: the exposure time and temperature.  All microorganisms are susceptible to varying degrees, to the action of heat. Heat causes denaturation of proteins, fusion and disruption of membranes and / or irreversible oxidative processes in microorganisms.

Damp Heat:  Moist heat causes protein denaturation and coagulation. These effects are mainly due to two reasons:

1. Water is a very reactive chemical species and many biological structures are produced by reactions that remove water.
2. Water vapor has a heat transfer coefficient much higher than air.

Autoclave: Sterilization is performed by the water vapor pressure. The model used is that of Chamberland. Sterilize at 120 ° at one atmosphere pressure (these can be different) and leave the material for 20 to 30 minutes. Team:  It consists of a copper boiler, supported by a metal outer sheath, which at the bottom receives heat by burning gas or an electrical resistance, this is closed on top by a brass cap. This lid has three holes, one for the gauge, one for the exhaust steam as Robinet and the third to a safety valve which operates by spring or counterweight.

Operation:  Place water in the boiler, ensuring that your level does not reach to objects that are arranged on a wire rack. Ensuring the lid is closed without tightening the bolts and heat is given, leaving open the valve until all air is dislodged and start salidÔ9de as a jet vapor continuous and abundant. Sterilization by discontinuous action of water vapor, is based on the principle Tyndal bacteria that resist a heating session, made under certain conditions, may be destroyed when the same operation is repeated at intervals separated and in several sessions. It is by means of autoclave Chamberland, leaving open the valve, or is operating at normal pressure. It may also be performed at lower temperatures, 56 º or 80 º occupy avoid decomposition of the substances to be sterilized by high temperatures.

Advantages of moist heat:

1. Rapid heating and penetration
2. Destruction of bacteria and spores in a short time
3. Do not leave toxic residues
4. There is a low deterioration of the displays
5. Economic

Disadvantages of moist heat:

1. It allows sterilizing solutions forming emulsions with water
2. It is corrosive to certain metal instruments
3. Dry heat:
4. The dry heat causes drying of the cell, is that high levels of toxic electrolyte membrane fusion. These effects are due to heat transfer from the materials to the microorganisms in contact with them.
5. The destructive action of heat on proteins and lipids requires a higher temperature when the material is dry or the water activity of the medium is low.

 Stoves: Double chamber, the hot air generated by a resistance, flowing through the main cavity and the space between the two chambers, a temperature of 170 ° C for the metal instrumental and 140 ° C for the contents of the drums.  Temperature stability is maintained through metal thermostats, that being rarefied by heat, cut the electrical circuit.

Benefits of Dry Heat:

1. It is corrosive to metals and instruments.
2. It allows the sterilization of powdered substances and non-aqueous, viscous and non-volatile substances.

Disadvantages of dry heat:

Requires more time for sterilization, moist heat on because of the low penetration of heat radiation.

Its action depends on:

1. The type of radiation
2. Exposure time
3. The dose
4. Ionizing
5. They have high permeability and are used to sterilize materials thermolabile (heat sensitive) as disposable syringes, catheters, etc.. They are used on an industrial scale for their costs.

 Ultraviolet Rays:  Affect the DNA molecules of microorganisms. They are scarcely used for penetrating and surfaces are used for sterilization in operating rooms.

Gamma:  Its use is based on knowledge of atomic energy. This type of sterilization applies to products or materials thermo labile and of great importance in the industrial field. You can sterilize antibiotics, vaccines, food, etc..

Filtration: Used membrane filters with pores of a given size. The pore size depends on the use to which it intends to submit the sample. The filters used can hold no viruses or mycoplasma, the latter are at the limit of separation as the pore diameter is used.

The filtration is used for thermo labile oil emulsions or solutions. Its used to sterilize oils, some types of ointments, ophthalmic solutions, intravenous solutions, diagnostic drugs, radiopharmaceuticals, cell culture media and solutions of antibiotics and vitamins.

There are three basic types of filters: They consist of a fibrous or granular material pressing, folding, on, or stuck inside the flow channels. In this type of filter retention of particles occurs by a combination of absorption and mechanical retention in the matrix.

Membrane filters: They have a continuous structure, and retention is mainly due to particle size. Smaller particles to pore size are retained in the matrix of the filter due to electrostatic effects.

• Written by Rajinder Soni.
• In category Medicine & Surgery.
• 15 years ago.

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