When a manufacturer give recommendations to sterilize an item in a prevac cycle, can you also run that item in a gravity cycle since the gravity cycle is a lower temperature? My thoughts are that you sterilize an item the way the manufacturer recommends because that is the way they validated sterilization.

Jamie

Jamie

the difference between pre-vac and gravity cycles are the methods used for air removal. The gravity cycle relies on air being pushed out by steam movement - difficult foe air-retentive or packed items. The pre-vac cycle uses an active air-removal process designed to extract air from difficult load items. If the manufacturer recommends a pre-vac cycle then there are good reasons for this and the recommendation should be followed. Incidentally, gravity cycles are not necessarily performed at lower temperatures tha pre-vac cycles

Peter Hooper

Dear Jamie,

I just want to give an additional comment. In the first place on the choice of the sterilization temperature. Unless there are specific contraindications, it is better to sterilize an instrument for a short period of time on the higher temperature (less stress) than for a long time on the lower temperature. In the second place about the choice of the process. Jan Huys says in his book "Sterilization of Medical supplies by Steam, Volume 1, General Theory":

"Remarks on sterilizers based on the process with air removal by downward displacement: ...Although the process has a number of advantages such as the simplicity of the technology, the low price of the equipment which is easy to maintain, the process has a number of serious disadvantages:

• Full air removal by downward displacement from wrapped load and hollow instruments is not possible. Therefore this type of sterilizer is only accepted as safe for unwrapped or lightly wrapped, non hollow instruments and bottled fluids.
• As it takes time before all load is in touch with the steam it is necessary that the time for a sterilization cycle is considerably longer... (editorial note: generally the sterilization time is 30 minutes at 121 °C for gravity displacement processes).
• The loading method strongly influences the removal of the air. Therefore the loading has to be done very carefully allowing a free passage of the steam and air everywhere in the chamber.
• Goods may be not fully dry after the process is ended. This causes extra danger of recontamination.

Because of these problems: According to the ISO and CEN international standards on sterilization, the process with downward displacement is only allowed for unwrapped instruments and bottled fluids."
In conclusion: whenever possible a prevacuum cycle is the better choice.

Best regards,
Wim Renders
p.s. see also the answers on question Q00100.