Sterilization and Disinfection M.N Priyadarshanie B.Sc.Nursing(Hons)

I. Sterilization It is one of the basic steps in surface asepsis. Definition: Sterilization refers to the use of different procedures to destroy all forms of microorganisms including bacterial spores.

What to sterilize? It is mandatory to sterilize : all instruments that penetrate soft tissues and bone. Instruments that are not intended to penetrate the tissues, but that may come into contact with oral tissues. If the sterilization procedure may damage the instruments, then, sterilization can be replaced by Disinfection procedure

II. Disinfection It a is less lethal process than sterilization. Definition: It is a procedure intended to reduce microorganisms as far as possible (but not bacterial spores). Thus, disinfection can never replace sterilization

Which procedure to use? Procedure Category Sterilization Items in each category Category Sterilization Items that: (1) enter the tissue; (2) Enter vascular system; (3) through which blood flows Critical High level disinfection Items that: (1) touch mucous membranes; (2) touch non-intact skin (e.g. endoscopes, respiratory therapy equipment, and diaphragms) Semi-critical Low level disinfection Items such as bedpans, blood pressure cuffs, and bedside tables Non-critical

I. Sterilization - Process

Sterilization – Instrument Packing Often instruments are packed for sterilization Packing depend on the intended shelf life after sterilization. The available packing options are: Textile has shelf life of 1 month Paper has shelf life of 1-6 months Nylon, glass, and metal have shelf life of 1 year if tightly closed

Sterilization Principles There are 3 different sterilization principles: Heat sterilization Chemical sterilization Radiation sterilization Each principles is discussed in the following sections.

1. HEAT STERILIZATION

1. Heat Sterilization Advantages: It is the simplest, most effective and inexpensive method. There are 2 procedures depending on the tolerance of the material used: Steam sterilization (Autoclaving) Dry heat sterilization

1.a. Heat – Steam Sterilization Use saturated steam above 100º C on packed items. Objects occupy 4/5 of autoclave volume to facilitate circulation. Process is divided into 3 periods as follows: Pre-vacuum period: air is withdrawn from device Sterilizing period: steam is introduced under pressure t specific temperatures & times. Post-vacuum: steam is withdrawn to dry autoclave

Steam Sterilization Advantages & Disadvantages good penetration maintains integrity of liquids (e.g. Lubricants) due to the 100% humidity within the chamber. Disadvantages: Non stainless steel metal items corrode may damage plastic and rubber items sharp instruments get dulled.

1.b. Dry-Heat Sterilization Involves heating at atmospheric pressure and often use a fan to obtain uniform temperature by circulation. Heat at 180º for half hour , 170º for 1 hr., or 160º C for 2 hrs. Times are the periods during which object is maintained at the respective temperature

Dry-Heat Sterilization Disadvantages Less reliable than autoclaving sharp instruments get dulled Many materials do not tolerate dry heat

2. CHEMICAL STERILIZATION

2. Chemical Sterilization - Types The chemical compounds used can be: Gas Sterilization Liquid Sterilization Generally, chemical sterilization procedures have the disadvantages of presenting health hazards to users (e.g. poisonous, flammable )

The gas used in this procedure is ethylene oxide. Keep objects in constant atmospheric humidity. Heat to temperatures between 30º and 60º C. maintain for a period of 10 hrs. Residual ethylene oxide must be ventilated Formalin gas autoclaves have been developed for sterilizing endoscopes and anaesthetic apparatus. 2.a) Gas Sterilization

Gas Sterilization – Disadvantages Ethylene oxide (& formalin) autoclaves have the following disadvantages: Difficult to operate Unsuitable for hospitals but used in industry (e.g. for sterilizing disposable materials that can not tolerate high temperatures).

2.b) Liquid Sterilization Can be performed with buffered glutaric aldehyde. Procedure: Immerse object in liquid for several hours. Rinse with sterile water after end of procedure.

3. RADIATION STERILIZATION

3. Radiation Sterilization Provides effective way of sterilization when used in high doses. Gamma radiation Procedure: Expose objects for about 24 hrs.

Radiation Sterilization Advantages and Disadvantages Clean process Dry process Ensures full exposure of object from all directions Disadvantages: Posses threat to humans (radiation) Lengthy process Requires very qualified personnel

II. DISINFECTION

Disinfection - Types Disinfection can not kill all microorganisms but only reduce its number. Disinfection can be accomplished with: Heat disinfection Chemical disinfection Object that can be disinfected are bedpans, patient skin before operation and surgeon hands before putting gloves.

1. Heat Disinfection It is accomplished by boiling water at atmospheric pressure for at least 20 min’s

2. Chemical disinfection Number of different agents are used according to tolerance of objects and infectious agents. Using phenol with cleaning component destroy the membrane of microorganisms. Using 70% alcohol for skin which denatures proteins of microorganisms. Use soap containing hexachlorophene for hands. In case of hepatitis use 5% solution of chloramines or heat disinfection

Asepsis – Summary

Disinfection and Sterilization - New methods

Chemical Antimicrobials Agent Mechanisms of Action Comments Surfactants Membrane Disruption; increased penetration Soaps; detergents Quats (cationic detergent) Denature proteins; Disrupts lipids Antiseptic - benzalconium chloride, Cepacol; Disinfectant Organic acids and bases High/low pH Mold and Fungi inhibitors; e.g., benzoate of soda Heavy Metals Denature protein Antiseptic & Disinfectant; Silver Nitrate Halogens Oxidizing agent Disrupts cell membrane Antiseptic - Iodine (Betadine) Disinfectant - Chlorine (Chlorox) Alcohols Denatures proteins; Disrupts lipids Antiseptic & Disinfectant Ethanol and isopropyl Phenolics Disrupts cell membrane Disinfectant Irritating odor Aldehydes Denature proteins  Gluteraldehyde - disinfectant (Cidex); Formaldehyde - disinfectant Oxidizing agents Denature proteins Hydrogen peroxide – antiseptic; Hydrogen peroxide – disinfectan; Benzoyl peroxide – antiseptic Chemical Antimicrobials

Soaps are sodium or potassium salts of fatty acids, a natural product Detergents, instead, are artificial surfactants While soaps are always negatively charged, some detergents are negatively charged while others are positively charged One example of a positively charged detergent are quaternary ammonium compounds (a.k.a., quats) Soap & Detergents

Halogens are the seventh (VII) column of the periodic table of elements Two halogens are regularly employed as antimicrobials: Iodine and Chloride Iodine: commonly used as an antiseptic against all microbes, fungi, and viruses Iodine: It inhibits protein synthesis and oxidizes –SH groups of amino acids Chlorine: Used as a disinfectant (10% bleach) Chlorine: Hypochlorous acid (HOCl) is a product, formed in water, that is the active form of the disinfectant Chlorine: Applied in treatment of drinking water, swimming pool, and sewage Halogens

and even in the presence of organics, Glutaraldehyde is capable of effectiving sterilization—at room temperature, even against endospores, and even in the presence of organics, but achieving sterilization requries many hours of exposure… and it is nasty stuff to work with! Glutaraldehyde

Conclusion In summary: Sterilization and disinfection are costly and time consuming process However, it is an essential in all health care facilities to avoid spread of diseases. It depends on the ehtics of the instrument users. Users should keep in mind that contaminated instrument present risk to patient as well as the user himself.

Thank you.