Table of Contents
Physical sterilization
- Thermal
- Filtration
- Radiation
Thermal
- Steam sterilization is the most commonly employed method of sterilization of instruments and equipment.
- Different types of autoclaves are
- pressure steam sterilizer
- steam pressure sterilizer
- vacuum steam sterilizer
- dressing sterilizer
- gravity displacement sterilizer
Points to be considered
- Instrument packs are positioned vertically (on edge ) and longitudinally in autoclave
- A 13 minutes sterilizing cycle (exposure to saturated stem at 1210C) is a safe minimum required
- Large linen packs require 30 minutes at 1210C
- Once sterilized, sterile packs should be stored in closed cabinets. All packs should be dated.
- Sharp instruments ¾ scissors, needles; surgical instruments can be sterilized by this method.
Dry heat sterilization
- Dry heat destroys microorganisms primarily by oxidation process.
- It is used to sterilize those materials for which moist heat cannot be used either due to deleterious effects on the material or material being impermeable to steam e.g: oils, powders, glass surgicals etc.
- Slow process and long exposure time at a high temperature is required as spores are relatively resistance to dry heat.
Methods
- Direct exposure of instruments to flame – not reliable.
- Hot air oven – most common method.
- An exposure to dry heat at a temperature of 1600C for 60 min will achieve sterilization equal to that of moist heat at 1210C for 15 min, at 151 lbs pressure.
- Temperature time combinations for dry heat sterilization
- 1200c for 8.0 hours
- 1400c for 2.5 hours
- 1600c for 60 minutes
- 1700c for 40 minutes
- Exposure time relates to the time after specific temperature has been achieved and don’t include heating lags.
- Clean gowns, paper wrapped material, swabs, Petridis – 1200c for 8 hours
- Stainless steel lens and glass ware – 1600c for 60 min
Filtration
- Filtration is used in air conditioning system to remove particles as small as 0.3 μm in diameter and also used to filter-sterilize heat labile solutions.
Radiation
- Ultraviolet light is used for surface sterilization.
- Ionizing radiations, Beta and cathode rays are used to sterilize heat sensitive prepackaged surgical materials.
- Example: Surgical mask – to produce two fold effect. CHEMICAL AGENT
- An ideal chemical agent should have following properties
- kill all pathogenic microorganism
- work effectively in short period of time
- exert residual action
- not corrode, dry or stain
- be stable, odorless, non toxic
- be effective in presence of organic matter
- not be inactivated by other concurrently used chemicals
Chemical sterilization
- Germicidal solutions Glutaraldehyde, Beta propiolactone
- Ethylene oxide
Chemical sterilization by gases
- Ethylene oxide acts by inactivating the DNA molecules in the microbial cells thus preventing cell reproduction. Temperature – 120 to 140oF
- Eg: ethylene oxide, formal dehyde and beta propiolatone (generally used)
- Sharp edged instruments – Scalpel blades, hypodermic needles.
Agents in solution form
Alcohol
- Ethyl alcohol (70%), Isopropyl alcohol (90%) are commonly used
- Presence of water easily denatures the protein.
- 70% alcohol is more qermicidal than absolute alcohol.
- Isoprophyl alcohol is more bacterial than ethyl alcohol
- Sterilization can be done by immensities continuously. Eg: Needles.
Aldehyde
Formaldehyde and flutasaldehyde (cidex, parvo cide )
Formaldehyde
- Available as formalin 37% solution of formaldehyde and water.
- Used as gas for fumigation.
- Irritant to skin and mucous membranes.
Oxidizing agent e.g. Halogens
- Inorganic Iodine compounds
- Organic Iodine compounds