A. Physical sterilization
- Thermal
- Filtration
- Radiation
B. Chemical sterilization
- Germicidal solutions Glutaraldehyde, Beta propiolactone
- Ethylene oxide
Table of Contents
A. Physical sterilization
a. Thermal sterilization
i. Moist heat sterilization:
- Steam sterilization is the most common 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 an autoclave.
- A 13-minute sterilizing cycle (exposure to saturated steam at 121 degree celsius) is a safe minimum requirement.
- Large linen packs require 30 minutes at 121 degree celsius.
- After sterilization, sterile packs should be stored in closed cabinets. All packs should be dated.
- For e.g., Sharp instruments ¾ scissors, needles; surgical instruments
ii. Dry heat sterilization
- Dry heat destroys microorganisms primarily by the oxidation process.
- 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, etc.
- A slow process and long exposure time at a high temperature are required as spores are relatively resistant to dry heat.
Methods of dry heat sterilization:
- Direct exposure of instruments to flame – not reliable.
- Hot air oven – most common method.
- Exposure to dry heat at a temperature of 160 degrees celsius for 60 min will achieve sterilization equal to that of moist heat at 121 degrees Celsius for 15 min, at 151 lbs pressure.
- Temperature time combinations for dry heat sterilization
- 120 degrees celsius for 8.0 hours
- 140 degrees celsius for 2.5 hours
- 160 degrees celsius for 60 minutes
- 170 degrees celsius for 40 minutes
- Exposure time relates to the time after a specific temperature has been achieved and doesn’t include heating lags.
- Clean gowns, paper-wrapped materials, swabs, Petridis – 120 degrees celsius for 8 hours
- Stainless steel lens and glassware – 160 degrees celsius for 60 min
b. Filtration
- Filtration is used in air conditioning systems to remove particles as small as 0.3 μm in diameter and is also used to filter-sterilize heat-labile solutions.
c. Radiation
- Ultraviolet light for surface sterilization.
- Ionizing radiations, Beta and cathode rays to sterilize heat-sensitive prepackaged surgical materials.
- Example: Surgical mask – to produce a two-fold effect.
B. Chemical sterilization
An ideal chemical agent should have the following properties:
- Should kill all pathogenic microorganisms.
- Must work effectively in a short period of time.
- Should have residual action.
- Must not corrode, dry, or stain.
- Should be stable, odorless, and nontoxic.
- Must be effective in presence of organic matter.
- Should not be inactivated by other concurrently used chemicals.
Chemical agents
a. Alcohol
- Ethyl alcohol (70%), Isopropyl alcohol (90%)
- The presence of water easily denatures the protein.
- 70% alcohol is more germicidal than absolute alcohol.
- Isopropyl alcohol is more bacterial than ethyl alcohol
- Eg: Needles
b. Formaldehyde
- Available as formalin 37% solution of formaldehyde and water.
- Used as gas for fumigation.
- Irritant to skin and mucous membranes.
c. Oxidizing agents e.g. Halogens
- Inorganic Iodine compounds
- Organic Iodine compounds
d. Surfactants – Soaps, detergents
e. Phenolic derivatives – carbolic acid
f. Chemical sterilization by gases;
- Ethylene oxide acts by inactivating the DNA molecules in the microbial cells thus preventing cell reproduction. Temperature – 120 to 140F
- Eg: ethylene oxide, formaldehyde, and beta propiolatone
- Used for sharp-edged instruments – Scalpel blades, hypodermic needles.