STERILIZATION

Sterilization destroys all microorganisms, including bacterial
endospores.Sterilization should be used for instruments, surgical gloves and other itemsthat come in direct contact with the blood stream or normally sterile tissues (Spaulding 1939). It can be achieved by high-pressure steam (autoclave), dryheat (oven), chemical sterilants (glutaraldehydes or formaldehyde solutions)or physical agents (radiation). Because sterilization is a process, not a single
event, all components must be carried out correctly for sterilization to occur.
Effectiveness
To be effective, sterilization requires time, contact, temperature and, with
steam sterilization, high pressure. The effectiveness of any method of
sterilization is also dependent upon four other factors:
1. The type of microorganism present. Some microorganisms are very
difficult to kill. Others die easily.
Note: Although rinsing an
item with alcohol and then
igniting it with a match
(flaming) sometimes is
suggested as a method of
sterilization, it is not
effective!
2. The number of microorganisms present. It is much easier to kill one
organism than many.
3. The amount and type of organic material that protects the
microorganisms. Blood or tissue remaining on poorly cleaned
instruments acts as a shield to microorganisms during the sterilization
process.
4. The number of cracks and crevices on an instrument that might
harbor microorganisms. Microorganisms collect in, and are protected
by, scratches, cracks and crevices such as the serrated jaws of tissue
forceps.
Finally, without thorough cleaning, which removes any organic matter
remaining on the instruments that could protect microorganisms during thesterilization process, sterilization cannot be assured, even with longer sterilization times.
METHODS OF HEAT STERILIZATION
High-pressure, saturated steam using an autoclave, or dry heat using an oven,
are the most common and readily available methods used for sterilization.
High-pressure steam sterilization is an effective method of sterilization but
is the most difficult to do correctly (Gruendemann and Mangum 2001). It is
generally the method of choice for sterilizing instruments and other itemsused in healthcare facilities. Where electricity is a problem, instruments can be sterilized in a nonelectric steam sterilizer using kerosene or other fuel as a
heat source.

Dry-heat sterilizers (ovens) are good in humid climates but need a
continuous supply of electricity, making them impractical in many remote
(rural) areas. Furthermore, dry-heat sterilization, which requires use of highertemperatures, can be used only with glass or metal objects—it will melt othersubstances.
Standard Conditions for Heat Sterilization
Steam sterilization (Gravity): Temperature should be 121􀁱C (250􀁱F);
pressure should be 106 kPa (15 lbs/in2); 20 minutes for unwrapped items; 30
minutes for wrapped items. Or at a higher temperature of 132􀁱C (270􀁱F),
pressure should be 30lbs/in2; 15 minutes for wrapped items.
Allow all items to dry before removing them from the sterilizer.
Note: Pressure settings (kPa or lbs/in2) may vary slightly depending on the
sterilizer used. When possible, follow manufacturers’ recommendations.
Dry heat:
􀁸􀀃 170􀁱C (340􀁱F) for 1 hour (total cycle time—placing instruments in
oven, heating to 170􀁱C, timing for 1 hour, and then cooling—is from 2–
2.5 hours), or
􀁸􀀃 160􀁱C (320􀁱F) for 2 hours (total cycle time is from 3–3.5 hours).
Remember:
􀁸􀀃 Exposure time begins only after the sterilizer has reached the target
temperature.
􀁸􀀃 Do not overload the sterilizer. (Leave at least 7.5 cm [3 inches] between
the items and walls of sterilizer.) Overloading alters heat convection and

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