Heat

HEAT

Moist heat

  • Autoclaving (Steam under pressure), direct stream contact is the basis of steam sterilization. An autoclave is an apparatus  used for achieving sterilization by steam under pressure. It is of two types Viz. Vertical autoclave and Horizontal autoclave.
  • It is fitted with automatically regulated pressure gauze and can withstand at least 60 pound pressure per square inch.
  • At 15 pound pressure per square inch, the temperature wills rise to 121ºC and as the pressure rises the temperature will also rise accordingly.
  • A temperature of 121ºC at 15 pound pressure for 15 minutes is sufficient even to destroy vegetative cells and spores.
  • The following point should be kept into consideration while autoclaving
    • Materials to be sterilized should be completely dry.
    • The surgical pack should not be more than 30x40 cm in size so that it can be accomodated into the autoclave drum.
    • The folding of the towels, gown set, should be done in the accordion folds so that they so not form a dense instrument mass.
    • The locks of the various instruments must be left unclamped. The instrument joints must be free from grease (or) oil.
    • Liner wrappers of double thickness should be used instead of paper wrappers because all papers are not steam permeable.
    • Any impervious material like rubber sheets should be covered with linen and then loosely folded to allow easy access to the steam.
    • In drums the Packages should be placed in such a way that the steam can displace air down and outwards through the discharge pipe.
    • Nothing should rest directly on the floor of the autoclave.
    • After keeping the material to be sterilized in autoclave and turning it on, the outlet of the vacuum valve should be kept open till all the air is removed by incoming steam.
    • The outlet should be closed when the steam pressure builds up.
    • The surgical pack (or) other material is sterilized at 121ºC at 15 pounds pressure for 15 minutes. If the pack is large enough it should be sterilized for 20 to 30 minutes.
    • After sterilization is over, the autoclave is turned off. The outlet valve is opened to reduce the pressure to zero.
    • The water tap is opened to drain the chamber and then closed. The autoclave is opened and the surgical drum is closed and sealed immediately.
    • It is advisable to conduct autoclave testing at periodic intervals by putting testing at periodic intervals by Putting test organisms in a special packet and after sterilization in autoclave, testing its sterility.
    • Note: Tight packing and insufficient rest period may damp (or) wet the articles.
    • Excessive pressure, temperature, inadequate air discharge and lack of powdering at the time packing may decompose rubber goods.

Dry heat (Hot air oven)

  • Dry heat is used for sterilization of substances which cannot be steam sterilized e.g oils – mineral oil, which cannot be steam sterilization requires longer time.
  • The temperature in them is attained very quickly and 180ºC for 10 minutes is sufficient for sterilization.

Boiling in water

  • The boiling in water is not destructive to spores, however, addition of (2% )sodium carbonate is effective for sterilization and requires five minutes to kill the spores.
  • Boiling affects the sharp edges of the instruments and is destructive to rubber goods and glass wares.
  • At high altitude it may not attain the sufficient temperature and may not be effective.

Flame

  • This method of sterilization is efficient, however, limited to wire loops, metal probes, teat directors, teat canula, small tray etc.
  • The instruments to be sterilized are kept in a large stainless steel tray.
  • Methylated spirit 5 -10 ml is poured over the surface and ignited.
  • Care should be taken that fire may not spread.
  • The article to be sterilized should be absolutely dry and if it is large, it should be tilted slightly, during flaming spirit should not be poured on while there is still a flame.

Last modified: Wednesday, 9 May 2012, 5:43 AM