(2) Biological controls. A biological spore strip containing Bacillus
stearothermophilus should be tested once a week in each sterilizer. The biological
spore strip is incubated according to the manufacturer's recommendations and recorded
in the sterilizer's permanent records. This spore strip tests the effectiveness of steam
sterilization. If a positive culture (a culture with living microorganisms after sterilization)
is reported during the testing, the affected sterilizer must be checked out by medical
maintenance, who will take appropriate action.
(3) Chemical controls. Chemical indicators are sensitive to time,
temperature, and steam penetration and are used in every package sterilized. Pressure
sensitive tape (see figure 3-14) is used to secure packaged items and as a label on
items to be sterilized. The paper backing of this pressure-sensitive adhesive changes
color when it is exposed to high-temperature steam giving definite indication that the
item has been processed through a sterilizer but not necessarily successfully sterilized.
Chemically treated paper strips are placed in the center of packs to be sterilized. It also
changes to a distinctive color when proper sterilization conditions have occurred within
the pack. See figure 3-18.
Indicators show that the article has been exposed to the sterilization process.
They do not guarantee sterilization.
Figure 3-18. Chemically treated paper strip.
(4) The Bowie-Dick test. A fourth type test is used to determine whether air
removal from the chamber and load is adequate in prevacuum type sterilizers. It should
be used in the first cycle each day to determine whether the sterilizer is removing the air
within the chamber properly. As mentioned previously, you learned that air-steam
mixture results in a lower temperature and hinder the sterilization process.
3-13. GAS STERILIZATION
The gas sterilization process consists of air evacuation, humidification,
sterilization, gas evacuation, and admission of filtered air to relieve the vacuum. Only
those items that are heat-sensitive and cannot withstand steam sterilization will be gas
sterilized with ethylene oxide. Never gas-sterilize any item that can be steam-sterilized.
a. Advantages of Ethylene Oxide Sterilization. It is easily available; it is
effective against all types of microorganisms; it penetrates through masses of dry
material easily; it does not require high temperature, humidity or pressure; it is
noncorrosive and non-damaging to items that are heat and moisture sensitive.
b. Disadvantages of Ethylene Oxide Sterilization. It requires a long exposure and aeration
period; it is expensive; it is toxic, it is explosive.