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Chemical and Autoclave Sterilization Methods Outlined in Annex III of the WHO Infection Control Guidelines for Transmissible Spongiform Encephalopathies

The three most stringent sterilization methods for heat-resistant instruments described in Annex III of the WHO guidelines are listed below; the methods are listed in order of more to less severe treatments. Sodium hypochlorite may be corrosive to some instruments, such as gold-plated instruments. Before instruments are immersed in sodium hypochlorite, the instrument manufacturer should be consulted about the instrument’s tolerance of exposure to sodium hypochlorite. Instruments should be decontaminated by a combination of the chemical and recommended autoclaving methods before subjecting them to cleaning in a washer cycle and routine sterilization.

1- Immerse in a pan containing 1N sodium hydroxide (NaOH) and heat in a gravity displacement autoclave at 121°C for 30 min; clean; rinse in water; and subject to routine sterilization.
[CDC NOTE: The pan containing sodium hydroxide should be covered, and care should be taken to avoid sodium hydroxide spills in the autoclave. To avoid autoclave exposure to gaseous sodium hydroxide condensing on the lid of the container, the use of containers with a rim and lid designed for condensation to collect and drip back into the pan is recommended. Persons who use this procedure should be cautious in handling hot sodium hydroxide solution (post-autoclave) and in avoiding potential exposure to gaseous sodium hydroxide, exercise caution during all sterilization steps, and allow the autoclave, instruments, and solutions to cool down before removal. An experiment pdf icon[PDF – 88KB] conducted by Food and Drug Administration (FDA) investigators indicated that the use of appropriate containment pans and lids prevents escape of sodium hydroxide vapors that may cause damage to the autoclave (Brown and Merritt. Am J Infect Control 2003;31:257-260).]

2- Immerse in 1N NaOH or sodium hypochlorite (20,000 ppm available chlorine) for 1 hour; transfer instruments to water; heat in a gravity displacement autoclave at 121°C for 1 hour; clean; and subject to routine sterilization.
[CDC NOTE: Sodium hypochlorite may be corrosive to some instruments.]

3- Immerse in 1N NaOH or sodium hypochlorite (20,000 ppm available chlorine) for 1 hour; remove and rinse in water, and then transfer to open pan and heat in a gravity displacement (121°C) or porous load (134°C) autoclave for 1 hour; clean; and subject to routine sterilization.
[CDC NOTE: Sodium hypochlorite may be corrosive to some instruments.]

FDA investigators evaluated the effects to surgical instruments of the steps involved in the sterilization protocols listed above; some of the protocols they assessed subjected the instruments to harsher conditions than those prescribed above. Their findings indicate that much of the damage from autoclaving in sodium hydroxide was cosmetic and would not affect the performance or cleaning of the instruments. Soaking in sodium hydroxide had the least damaging effect on instruments, but immersion in sodium hypochlorite bleach caused severe damage to some instruments. The article summarizing the findings of this experiment pdf icon[PDF – 211KB] by Brown et al. of the FDA was published in the Journal of Biomedical Materials Research (electronic version published October 2004).