Dear EFHSS

Again it is Venugopal from India seeking answers for, probably, silly questions that underdeveloped CSSDs in India put to you.

Reecently in one of the meetings a surgeon opined that sterilization at 134 C for 7-10 minutes is ideal for non-porous instruments than the conventional 121 C for 30 minutes(?). The reasons sited are

1. Low period of exposure and hence longer life to instruments and
2. Good quality of steam at 134 than at 121!!

I also believe that there is some sense to it but the problem we have is that 95% of the steam sterilizers we have are Gravity Displacement 121 degrees ones.

Is there any documentation to prove that 134 is better than 121 degrees? If so, is it applicable on GD sterilizers? I am interested to know.

Regards
Venugopal K.G.

Good day Venugopal,

Since 1985 I have used autoclaves where the user could select their preference in the type of cycle used. The normal cycle is a 3.5 minute exposure time @ 134 C (275 F) cycle. The second most common cycle selected is a 30 minute exposure @ 121 C (250 F) cycle. This is not commonly used, maybe one or two cycles a day in a large hospital. The 134 C cycle uses pulses of mechanical vacuum to remove the air from the sterilizing chamber, the 121 C cycle uses gravity displacement to remove the air at the beginning of the sterilizing cycle. Mechanical removal of air from the sterilizing chamber can overcome problems with trapped air that can not be removed by gravity displacement (due to improper loading, etc.). Some powered devices like certain drills need the 121 C cycle because the vacuum pulse used with the 134 C cycle pulls the lubricant out of the instrument. Some dense devices like a Meshgraft Dermatome need the 121 C cycle because they need a longer time to heat up to sterilizing temperature than ordinary instruments because they are so massive. Some plastic items deform or melt at 134 C, but are not affected by 121 C. Fine, delicate edges will oxidize more with longer cycle times, so the shorter cycle time helps the instruments last longer. But, if your instruments are rusting, you probably have bigger and different problems to address than the length of the sterilization cycle. On the other hand, the manufacturers of some steam sterilizable endoscopes recommend 134 C cycles because the glue holding the lenses in place can melt during the long exposure time of a 121 C cycle. High quality steam sterilizer chambers have a very long life and I have seen autoclaves that were converted from gravity only cycle to multi-cycle functionality. (This was performed by an independent company in a workshop in another city.) I don't know about the quality of the steam changing significantly with the different temperatures and pressures. For both types of sterilizing cycles discussed, you need "saturated" steam with a relative humidity of 97% - 100%. You want the steam as clean and free of contaminants as possible.

Regards, Pete Bobb

Dear,

Indeed on condition that the instruments can stand it (see Pete's answer), a cycle at 134°C is better for 2 reasons:

1. The overkill is much greater in a cycle at 134°C.
2. It is better for the instruments to undergo a treatment at a higher temperature for a shorter period of time.

The quality of the steam depends more on other factors than temperature (EN 285 describes the quality of water and steam for steam sterilization). Gravity displacement cycles can be run at 134°C. You have to take into account that the removal of air due to downward displacement is quite slow and that the rate of heating the load to the higher temperature is not substantially greater.

I advise you also to have a look at the report - in English - Adrie De Bruyn is refering to in his answer to question 100: "Optimalisation of the process for manually operated jacket steam sterilisers". You can find it under: www.rivm.nl/bibliotheek/rapporten/318902011.html

Kind regards,
Wim Renders