Sterilization and Disinfection
• It is keeping medical instruments free from
• This is accomplished by:
• 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
• If the sterilization procedure may damage the
instruments, then, sterilization can be replaced
by Disinfection procedure
• It a is less lethal process than sterilization.
• Definition: It is a procedure intended to reduce
microorganisms as far as possible (but not bacterial
• Thus, disinfection can never replace sterilization
Which procedure to use?
Category Items in each category Procedure
Items that: (1) enter the tissue; (2)
Enter vascular system; (3) through
which blood flows
Items that: (1) touch mucous
membranes; (2) touch non-intact
skin (e.g. endoscopes, respiratory
therapy equipment, and diaphragms)
Items such as bedpans, blood
pressure cuffs, and bedside tables
Sterilization – instrument Packing
• Often instruments are packed for sterilization to
be stored and handled without being
• Packing depend on the intended shelf life after
• 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
• There are 3 different sterilization principles:
1. Heat sterilization
2. Chemical sterilization
3. Radiation sterilization
• Each principles is discussed in the following
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
• Process is divided into 3 periods as follows:
– Pre-vacuum period: air is
withdrawn from device
– Sterilizing period: steam is
introduced under pressure to
specific temperatures & times.
– Post-vacuum: steam is
withdrawn to dry autoclave
Table shows samples of time-temperature relationships for steam
Advantages & Disadvantages
– good penetration
– maintains integrity of liquids (e.g. Lubricants) due
to the 100% humidity within the chamber.
– 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
• 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 temp.
– Less reliable than autoclaving
– Large temp difference may arise within device.
– sharp instruments get dulled
– Many materials do nottolerate dry heat
2. CHEMICAL STERILIZATION
2. Chemical Sterilization - Types
• The chemical compounds used can be:
a) Gas Sterilization
b) Liquid Sterilization
• Generally, chemical sterilization procedures have the
disadvantages of presenting health hazards to users
(e.g. poisonous, flammable, )
2.a) Gas Sterilization
• The gas used in this procedure is ethylene
– 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 ansthetic
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
– Immerse object in liquid for several hours.
– Rinse with sterile water after end of procedure.
3. Radiation Sterilization
• Provides effective way of sterilization when
used in high doses.
• Gamma radiation (from 60
– Objects on belt conveyer
– Expose objects to 25 to 30 kGy for about 24 hrs.
Advantages and Disadvantages
– Clean process
– Dry process
– Ensures full exposure of object from all directions
– Posses threat to humans (radiation)
– Lengthy process
– Requires very qualified personnel
Disinfection - Types
• As mentioned before, disinfection can not kill
all microorganisms but only reduce its
• 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 Disinfection
• It is accomplished by boiling water at
atmospheric pressure for at least 5 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
Heat RadiationChemical Heat Chemical
Gamma Boiling water Phenol
Asepsis – Summary
• In summary:
– Sterilization and disinfection are costly and time
– 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
Disinfection and Sterilization - New
Table 1. New methods in disinfection and sterilization
Process Agent Regulatory agency action
Disinfection Ortho-phthalaldehyde (Cidex
FDA cleared, October 1999
Not FDA/EPA cleared
Not FDA/EPA cleared
Sterilization Liquid sterilization process
Not FDA cleared
Rapid readout ethylene oxide
biological indicator (Attest)
Not FDA cleared
New plasma sterilizer
FDA cleared, January 1999
1. Ortho-Phth-alaldehyde (OPA)
• Chemical Sterilizaer
– not eye and nasal passages irritant
– has excellent stability over a wide range of pH (3 to 9)
– has a barely perceptible odor
– Like glutaric aldehyde, it has excellent material compatibility
– It stains proteins gray (including unprotected skin)
OPA vs. Glutaric Aldehyde
Table 2. Activity of glutaraldehyde and ortho-phthalaldehyde
against Mycobacterium bovis
Disinfectant Time for 6-log10
1.5% glutaraldehyde 28-36 minutes
2.5% glutaraldehyde 14-18 minutes
0.21% ortho-phthalaldehyde 4.8-6.3 minutes
Range of values from two different laboratories (4).
• Surface disinfectants such as phenols
– Effective in significantly reducing microbial
– Have long-term residual activity
3. Superoxidized Water
• Based on the concept of electrolyzing saline.
– The end product (water) is not damaging to the
• Available in the United Kingdom; Sterilox
• A New rapid automated liquid Chemical Sterilization
• The sterilant is produced, as needed, by automatic mixing
of solutions of hydrogen peroxide and formic acid.
– automatic cleaning process
– capability to process two flexible scopes at same time
– automated channel blockage and leak detection
– filter water rinsing and scope drying after sterilization
– hard-copy documentation of key process parameters
– user-friendly machine interface
– total cycle time less than 30 minutes
5. Hydrogen Peroxide Plasma
• A New Low-Temperature Sterilization
• Can be used for temperature-sensitive
6. low-temperature plasma
• Technique for decontaminating thermolabile
products without the severe drawbacks of gas
– Alternative to steam sterilization for sterilizing
easily corroding products or electronic instruments
– Takes less time.
• However, Steam sterilization proved to be the
cheapest method of sterilizing
Sterilization & Disinfection