Sterilization of surgical instruments and equipments

A. Physical sterilization

• Thermal
• Filtration
• Radiation

B. Chemical sterilization

• Germicidal solutions Glutaraldehyde, Beta propiolactone
• Ethylene oxide

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:

1. Should kill all pathogenic microorganisms.
2. Must work effectively in a short period of time.
3. Should have residual action.
4. Must not corrode, dry, or stain.
5. Should be stable, odorless, and nontoxic.
6. Must be effective in presence of organic matter.
7. 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.