Sterilization

STERILIZATION & ASEPSIS

By-DR. ABDUL RAZAKPOSTGRADUATE ORAL SURGERY

B.I.D.S, BANGALORE

Definitions

Antiseptic- a chemical that is applied to living tissues such as skin or mucous membrane to reduce the number of micro-organisms present through inhibition of their activity or destruction.

Disinfectant- a chemical used on nonvital objects to kill surface vegetative pathogenic organisms, but not necessarily spore forms or viruses.

Sterilization- a process by which all microbial forms are destroyed

Cleansing of the Instruments It is a pre requisite for effective disinfection or sterilization. It removes visible contamination but does not necessarily destroy micro-organisms. These debris such as blood, saliva & necrotic materials, form a protective covering for micro-organisms & prevent penetration of sterilizing medium. Hence instruments should be thoroughly clean before sterilization.

Cleansing agentsSoapsDetergentsFat solvent solutionsUltrasonic devices

Soaps & Detergents Commonly used aids in cleansing the instruments.

Soaps are salts of fatty acids.

Detergents are synthetic compounds.

Both act by reducing the surface tension on the instrument surface causing emulsification of the contaminants, which are then removed in the rinsing phase.

Both these are very limited antibacterial activity especially against gram positive organisms.

Fat solvent agents Acetone, Xylene & Ether are sometimes used in cleaning They are relative expensive, caustic to living tissues & probably less effective in overall cleaning ability than soaps & detergents These solutions should be thoroughly rinsed from the instrument surfaces prior to use because of their caustic nature to the living tissues

Ultrasonic Cleaning Devices The instruments such as bone burs or bone files, where solid particles are wedged into small crevice, require time consuming & careful scrubbing, with stiff wire brush.They can be better managed by ultrsonic cleaning devices. These devices act by converting electrical energy into vibratory sound waves, which then pass through soap solution containing instruments.

Disinfectants

AlcoholsAlcohols are overused as disinfectants, but their appropiate use is as antiseptic

Alcohols possess some anti-bacterial activity, particularly against gram positive organisms, but they are ineffective against spores & viruses.

They act by denaturing bacterial proteins.

Ethanol & Isopropyl alcohol are commonly used alcohols.

Alcohols require 10 minutes of contact with the organism for effective action.

They are more effective at 70% concentration than compared to higher concentration, because water speeds up the denaturing process.

Disadvantagea.They evaporate very quickly, when applied on the instruments, thus do not function effectively as disinfectants.

b.They are corrosive to carbon steel instruments.

c.Rubber articles when soaked in alcohol, absorb alcohol, when they come in contact with living tissues, they can cause reaction.

Aqueous Quaternary Ammonium CompoundsBenzalkonium chloride is most commonly used quaternary compound.

It is used as both disinfectant & antiseptic.

It is bactericidal effective against gram positive bacteria & certain gram negative bacteria.

It is ineffective against spores & viruses.

It acts altering the permeability of bacterial cellwall & thus permiting escape of phosphorous & nitrogen.

It also causes protein denaturation.

PhenolsPhenols are one of the oldest group of disinfectant.

Phenols are active against bacteria, fungi & many viruses, but inacitve against spores.

These are often used for disinfection of walls, floors & furniture.

They can corrode certain metals such as brass, aluminum & carbon steel. They can also cause damage to plastics.

Aldehyde CompoundsFormaldehyde (aqueous solution, formalin) & glutaraldehyde are very effective disinfectants.

Formalin because of its noxious odour & requirement of a18-30 hours of contact for effective action, is not in common use.

Glutaraldehyde requires 10 hours contact for its cidal action.

It is effective against vegetative bacteria, spores, fungi & viruses.

It acts by alkylation.

It is toxic & irritating & thus not used on certain surfaces as furnitures, walls & floors.

It may be used on metals, rubber, plastics & porcelain.

Thes instruments should be thoroughly rinsed with sterile water to remove compound, prior to contact with tissues.

Methods of SterilizationMost commonly employed methods of sterilization are Moist Heata)Boiling Waterb)Steam Heatc)Oil

Dry HeatGasIrradiation

Boiling WaterBoiling water maintains & conducts heat extremely well.

Its kills micro-organisms by coagulation of proteins.

It provides temp. of 100 c.

Exposure to this temp. for 10 mins kills bacteria & exposure of 24 hours kills spore forms.

It is ineffective against viruses.

Steam Heat Steam sterilization involves heating water to generate steam in a closed chamber called autoclave, producing moist heat that rapidly kills micor-organisms. It is the most practical, quickest, safest, effective method of sterilization.It kills by coagulation of proteins.

Advantages a.High penetrating capacity b.Transfer of large amount of heat to the surface of instruments

Disadvantagesa.Blunting & corrosion of sharp instrumentsb.Damage of certain rubber goods

Two types of Autoclave are availablea.Standard Autoclave- At 15 psi pressure, temp. 121c, time 10-12 mins.b.Flash Autoclave-At 29.4psi pressure, temp. 134c, time 3mins.

Instruments to be sterilized are packed before sterilization to maintain the sterility till they open when requiredMaterials used to pack can be fabric, paper, muslin cloth pouches, nylon bags & paper wrap cassettes.These material allow adequate penetration of steam for adequate sterilization To prevent corrosion of the instruments ammonia or dicyclohexylammonium nitrite can be added to the autoclave Addition of 2% sodium nitrate is also effective in preventing corrosion

Test for EfficiencySpore testing- can be done once a week with spore of Geobacillus Stearothermophillus

Thermocouple- it is thermometric testing. 1st recording taken from thermocouple inside the test pack. 2nd recording taken from chamber drain. This provide good guide about the speed of penetration

Autoclave tape- this is a tape printed with sensitive ink, that changes colour at specific temperature.

OilHot Oil baths have been used to sterilize metallic instruments.

Oil can reach a temp. of 175 c.

Submerging instruments at this temp. for 15 mins is necessary for sterilization.

Oil has poor penetration & poor sporicidal activity.

It is difficult to remove oil from instruments, especially from hand pieces.

It should never be used to sterilize syringes or needles with fear of oil embolism.

Dry HeatHot Air Oven may be used for instruments that will not be damaged by high temperature.

It requires 160c for 2 hours to accomplish sterilization.

This long period is required due to poor penetrating property of hot air & poor conductance of heat by dry air.

Dry heats kills by dehydration & oxidation.

Advantage of this method is that sharpness of the cutting instruments is maintained.

Disadvantage carbon steel instruments lose their hardness during dry heat.

GasEthylene oxide gas at temp. above 10.8c

It kills organisms by alkylation.

It is used to sterilize instruments that cannot withstand temp. but it highly toxic & can blister on contact with living tissues.

It is highly flammable, but this property can be controlled by mixing with carbon dioxide.

Other gas used for sterilization is formaldehyde, but it is less popular than ethylene oxide

IrradiationRadiation are of two typesa.Ionising radiationb.Non-ionising radiation

Ionising radiation such as X-rays, Gamma rays & High speed ElectronsHave high penetrating properties & commonly used in industries.Used to sterilize disposable materials such as needles, suture materials, cannulas & pharmaceuticals.

Non-ionising radiations such as ultraviolet light is used to purify air in operating room.It has no penetrating ability & is limited to air sterilization & preparation of immunizing antigens.

AntisepticsAn antiseptic is a chemical disinfectant that is diluted, to be safe for application on living tissues.

AlcoholsThey are weak antiseptic, with limited antibacterial activity.They are frequently used for skin antisepsis prior to needle puncture.Ethyl alcohol & isopropyl alcohol.

Aqueous Quaternary Ammonium CompoundsBenzalkonium Chloride is used as skin antiseptic.Its antimicrobial activity is restricted only to gram-positive organismsThus they are of limited use.

Iodophor CompoundThese are most effective antiseptics.

In these iodine is mixed with polyvinyl pyrolidone,(betadine) organic surface-active agent.

Their activity is by release of iodine from complex. This iodine kills the bacteria by oxidizing microbial protoplasm.

These compounds exhibit an effective activity against most bacterias, spores, viruses, & fungi.

Iodophor compounds build up on the skin after successive scrubs & this provides long lasting activity.

Operating Room ProceduresOperating room is a clean environment in which surgery is performed, but it is not sterile.The operating room provide a safe, efficient & user friendly environment.The walls, ceiling & floor are regularly disinfected by fumigation40% formalin is used as fumigator.Air is filtered by an ultraviolet device to reduce the bacterial count.

Only operating personnels are allowed to enter the operating roomBefore entering, they change into scrub suits & put on cap, mask & special ot slippers or shoes.Care should be taken not to touch any sterile clothings or instruments.

Hand ScrubHand scrub is 1st step toward aseptic surgical technique.It is the most important & successful method of controlling the spread of infection in the hospital.

Purpose of hand scrub is two folds- a.To remove the superficial contaminants & loose epitheliumb.To reduce the bacterial counts.

Scrubbing technique

Trim the fingernails & clean with disposable nail files.

Scrub each fingers & interfinger webbing.

Scrub the palm, forearm upto 2 inch above the elbow.

Rinse the excess of soap & antiseptic

Sterile towel is used to dry the hands.One hand is dried with one side of the towel.Other hand is dried with the other side of the towel.Drying is from fingers to elbow.

GlovesTwo types gloves are availablea.Latex gloveb.Rubber glove

Latex glove are more commonly used glove. If surgeon allergic to latex, rubber gloves can be used.Rubber gloves are thinner & provide better tactile sensation.

Gloving technique

Right hand grasps inside cuff surface of left glove.

Left glove is pulled into place.

Gloved fingers of left hand are inserted into cuff(outer surface) of right glove.

Right glove is pulled into place.

Cuff of left glove is unfolded.

Preparation of the surgical sitePreparation of surgical site is important to reduce contamination.It can be done by presurgical scrub with antiseptic solution.Iodophor solution is most effective solution for skin preparation.Lubricating ointment is applied on the eye & eye is tapped.Auditory meatus is plugged with guaze.Hair from the surgical site is shaved just prior to scrubbing the skin.

Principle of scrubbingShould begin in the centre & extend concentrically to the pheriphery.Once the centre has been scrubbed, it should not be touched with same quaze.Fresh sterile quaze should be used & should begin again from the centre.Skin preparation should take about 5 mins.

Draping the patientThe purpose of draping the patient is to isolate the surgical area from other parts of the body & also from nonsterile operating equipments & personnel.Draping steps are as follows:

Patient’s head placed on sterile sheet covered by two towels.

Towels are used to drape patient’s head

Additional towels are placed on the sides to isolate the surgical area.Towel clips are used to stabilize the towels.

ReferenceOral and Maxillofacial Surgery Vol.1- Daniel LaskinTextbook of Microbiology- AnantnarayanEssential of Medical Pharmacology- K D Tripathi