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

Sterilization and Disinfection

M.N Priyadarshanie B.Sc.Nursing(Hons)

I. SterilizationIt 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. DisinfectionIt 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?Category Items in each category Procedure

CriticalItems that: (1) enter the tissue; (2) Enter vascular system; (3) through which blood flows

Sterilization

Semi-critical

Items that: (1) touch mucous membranes; (2) touch non-intact skin (e.g. endoscopes, respiratory therapy equipment, and diaphragms)

High level disinfection

Non-criticalItems such as bedpans, blood pressure cuffs, and bedside tables

Low level disinfection

Sterilization – Instrument Packing

Often instruments are packed for sterilizationPacking depend on the intended shelf life after

sterilization.The available packing options are:

Textile has shelf life of 1 monthPaper has shelf life of 1-6 monthsNylon, glass, and metal have shelf life of 1 year

if tightly closed

Sterilization Principles There are 3 different sterilization principles:

1. Heat sterilization

2. Chemical sterilization

3. Radiation sterilization Each principles is discussed in the following

sections.

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:

a) Steam sterilization (Autoclaving)

b) 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– Pre-vacuum period: – air is withdrawn from device– Sterilizing period: steam is introduced under

pressure t specific temperatures & times.– Post-vacuum: steam is withdrawn to dry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 SterilizationAdvantages & Disadvantages

Advantages:good penetrationmaintains integrity of liquids (e.g. Lubricants) due to the

100% humidity within the chamber.

Disadvantages:Non stainless steel metal items corrodemay damage plastic and rubber itemssharp instruments get dulled.

1.b. Dry-Heat SterilizationInvolves 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

Disadvantages:Less reliable than autoclavingsharp instruments get dulledMany materials do not tolerate dry heat

2. Chemical Sterilization - Types

The chemical compounds used can be:a) Gas Sterilizationb) Liquid Sterilization

Generally, chemical sterilization procedures have the disadvantages of presenting health hazards to users

(e.g. poisonous, flammable )

2.a) Gas SterilizationThe gas used in this procedure is ethylene oxide.Procedure:

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.

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 SterilizationCan be performed with buffered glutaric

aldehyde.

Procedure:Immerse object in liquid for several hours.Rinse with sterile water after end of procedure.

3. Radiation SterilizationProvides effective way of sterilization when used in high

doses.Gamma radiationProcedure:

Expose objects for about 24 hrs.

Radiation Sterilization Advantages and DisadvantagesAdvantages:

Clean processDry processEnsures full exposure of object from all directions

Disadvantages:Posses threat to humans (radiation)Lengthy processRequires very qualified personnel

Disinfection - Types Disinfection can not kill all microorganisms but only

reduce its number. Disinfection can be accomplished with:

1. Heat disinfection

2. Chemical disinfection Object that can be disinfected are bedpans, patient skin

before operation and surgeon hands before putting gloves.

1. Heat DisinfectionIt is accomplished by boiling water at atmospheric

pressure for at least 20 min’s

2. Chemical disinfectionNumber 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 – SummaryAsepsis

Sterilization Disinfection

Heat RadiationChemical Heat Chemical

Steam

Dry heat

Gas

Liquid

Gamma Boiling water Phenol

Heat or chloramines solution

Hexachlorophene

70% AlcoholEthylene oxide

Formalin

Glutaric Aldehyde

Disinfection and Sterilization - New methods

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

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)

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

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!

ConclusionIn 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.