ISE789 End of Semester Review

Course Projects

• They are being graded.• You can stop by my office on Monday to

pick them up.

What we have covered

• Text on Healthcare– Organization and structure– Condition and methods– Position papers

• Biology for engineers– Disease and causes– Bioengineering

• Systems Engineering in Healthcare– Queueing models

Continued• Engineering for Medical Devices

– Requirements– Anatomy– Biomechanics– Bio Inert– Bio active

• Bactericidal metals and models– Silver and other bactericidal metals– Ions

• Disinfectants and sterilization – Chapter posted two weeks ago– Methods and application

The Exam

• Some multiple choice• Some short answers• Some problems• It will take you the entire time.

Sterilization and Disinfection

ISE789Dr. R. A. Wysk

Agenda

• What are disinfectants?• How do we disinfect, sterilize and clean?• Why do we disinfect?• What are the processes that can be used?

Microorganisms

• Some good• Some not so good• Sterilize – no living forms• Disinfect – remove certain life forms

Disinfect• Disinfectants are antimicrobial agents that are applied

to non-living objects to destroy microorganisms, the process of which is known as disinfection.– Cleaning an article of some or all of the pathogenic organisms

which may cause infection• A perfect disinfectant would also offer complete and full

sterilization, without harming other forms of life, be inexpensive, and non-corrosive.– There are no perfect disinfectants.

The hows and how tos

• Cause the minimal amount of disruption to human and physical environment.

• Long or short life activities– Surgery

• Alcohol• Betadine

– Aldehydes

Dry Heat Thermal MethodPrinciple/Conditions

Advantages Disadvantages Uses

Thermal inactivation: destroys by oxidation

Non-corrosive Simple design and principle

Less effective than moist heat; requires longer times and/or higher temperatures

Materials that are damaged by, or are impenetrable to, moist heat

Hot Air OvenPrinciple/Conditions

Advantages Disadvantages Uses

160-180oC for 2-4 hours

•penetrates water-insoluble materials (e.g., grease and oil) • less corrosive to metals and sharp instruments than

steam

• slow diffusion, penetration • loading, packing critical to performance • not suitable for reusable plastics

•anhydrous materials, such as oils, greases and powders •laboratory glassware, instruments •closed containers

Red Heat Flame MethodPrinciple/Conditions

Advantages Disadvantages Uses

Oxidation to ashes (Burning)

Rapid •initial contact with flame can produce a viable aerosol•possibility of accidental fire

Inoculating loops, needles, other disposable medical supplies

Incineration MethodPrinciple/Conditions

Advantages Disadvantages Uses

Oxidation to ashes (Burning)1 – 60 minutes at temperatures up to 1000o C

Reduces volume of waste by more than 95%

•improper use may lead to emission of pathogens in smoke• requires transport of infectious waste•excess plastic (>20%) content reduces combustibility

• for decontamination of waste items prior to disposal in landfill

Pasteurization MethodPrinciple/Conditions

Advantages Disadvantages Uses

Heating to below boiling point (generally 77oC) for up to 30 minutes

• can be used on heat sensitive liquids and medical devices •low cost

•Not particularly reliable •Milk and dairy products •some heat-sensitive medical equipment

Boiling MethodPrinciple/Conditions

Advantages Disadvantages Uses

Maximum temperature attainable is ~100o C for 10- 30 minutes

Minimal equipment needed

•Not reliable•Cumbersome

• Small instruments and equipment

Autoclaving MethodPrinciple/Conditions

Advantages Disadvantages Uses

• Steam under pressure15 – 90 minutes at temperatures up to 120o C at 5 psi•Steam under pressure4 – 20 minutes at temperatures up to 132o C at 27 psi

• Minimal time required• The standard for lab use, i.e., most dependable

•Loading and packing critical to performance• Items must be free of dirt and solid adhesions•Can damage heat sensitive items

• Penetration of sterile glassware •Decontamination of reusable supplies and equipment •Decontamination of infectious wastel

Autoclave

A Front Loading Autoclave

Autoclave

A Stove-top Autoclave

Ultraviolet Light

• 260 nm light wave sources (UV lamps)• Effective for a variety of pathogens

(bacteria, virus and fungus)– Poor penetration (limited to light permeable

goods, like water)– Particulate, like dust, decrease the

effectiveness– Light source must be cleaned routinely

Other methods

• Infrared radiation• Microwaves• Gamma radiation• Filtration

Chemical Sterilants and disinfectants

• Instruments that can not be sterilized using high temperatures may undergo a gas sterilization process such as ethylene oxide or other chemical germicides.

Chloride compounds (liquid bleach)Effective concentrations, contact time

Advantages Disadvantages Uses

•100 – 10,000 ppm (.01- 1%) free chlorine

•10 – 60 minutes

• broad spectrum •low cost •Widely available•Bactericidal at low temps

•Toxic, corrosive to skin and metals•Unstable•Inactivated by organic matter•Deteriorates under heat and light

•General disinfectant•Waste liquids•Surface contamination•Instruments

Calcium hypochloriteEffective concentrations, contact time

Advantages Disadvantages Uses

•100 – 10,000 ppm (.01 - 1%) free chlorine

•10 – 60 minutes

• broad spectrum •low cost •Widely available•Bactericidal at low temps

•Toxic, corrosive to skin and metals•Unstable•Inactivated by organic matter•Deteriorates under heat and light

•General disinfectant•Waste liquids•Surface contamination•Instruments

Iodine PreparationsEffective concentrations, contact time

Advantages Disadvantages Uses

•30 – 1,000 ppm (.003- .1%) free iodine

•10 – 30 minutes

• broad spectrum •Non-stinging •Less toxic•Less irritating

•Not consistent•Some iodophors support the growth of Pseudomonas

•Germicidal soaps•Surface decontamination•Instruments

AlcoholsPrinciple/Conditions

Advantages Disadvantages Uses

•70-80% ethanol•60-90% isopropanol•10 – 30 minutes

• low toxicity •low cost•Low residue•Non-corrosive

•Rapid evaporation•Flammable•Damage to rubber, plastic and shellac•Ineffective against spores

•Skin disinfectant• Counter-tops

Phenolic CompoundsPrinciple/Conditions

Advantages Disadvantages Uses

•400 – 50,000 ppm•10 – 30 minutes

• Tolerant of organic load •Leaves an active residue•biogradeable

•Pungent odor•Not sporicidal •Leaves a residue

•Antiseptic •some heat-sensitive medical equipment

Hydrogen PeroxidePrinciple/Conditions

Advantages Disadvantages Uses

•3 – 30% aqueous solution•10 – 60 minutes•6% for 30

minutes

•Rapid action•No residue•Low toxicity •low cost •Environmentally safe

•Limited sporicidal•Corrosive to some metals•Potentially explosive at high concentrations•Can be irritating to eyes

•Surface decontamination •Instruments and equipment

What to use? When?