Title:Sterilization
Definition
Sterilization is the process of killing or removing all forms of microorganisms, including
spores, from an object or environment to make it free from all viable forms of life.
Methods of Sterilization
1. Physical Methods
a. Natural Methods
Sunlight: Natural UV rays have mild germicidal effects, requiring continuous
exposure for around 8 hours to reduce microbial load.
b. Heat Methods
i. Dry Heat
Red Heat: Instruments are directly heated until glowing red (e.g., inoculating loops).
Flaming: Passing objects like forceps through a flame for quick sterilization.
Incineration: Complete destruction of contaminated waste materials by burning.
Hot Air Oven: Sterilizes glassware and metal instruments at 160°C for 1–2 hours.
Infrared: Uses radiant heat but is less commonly used today.
ii. Moist Heat
Below 100°C:
o Pasteurization: Reduces microbial load in heat-sensitive liquids (milk).
o LTLT: 63°C for 30 minutes
o HTST: 72°C for 15 seconds
At 100°C:
o Boiling: Kills most vegetative bacteria and viruses, though not all spores.
o Tyndallisation: Fractional sterilization method involving boiling on three
successive days to eliminate spores.
Above 100°C:
Autoclaving: Uses steam under pressure (121°C at 15 psi for 15–20 minutes); ideal
for surgical instruments and culture media.
2. Radiation Methods
Non-ionizing Radiation (UV Light): Damages microbial DNA; used for surface
sterilization in laboratories.
Ionizing Radiation (Gamma/X-rays): Penetrates deeply and sterilizes disposable
medical equipment.
3. Filtration (Mechanical Method)
Used for sterilizing heat-sensitive liquids such as vaccines and antibiotics.
Asbestos Filter: No longer commonly used due to health hazards.
Membrane Filter: Thin membranes with pores (as small as 0.22 microns) to trap
bacteria.
Sintered Glass Filter: Made of fused glass particles, useful in laboratories.
4. Chemical Methods
a. Liquid Chemical Sterilization
Alcohols: (e.g., 70% ethanol) Used for skin antisepsis and surface disinfection.
Aldehydes:
o Formaldehyde: Used for fumigation.
o Glutaraldehyde: Disinfects endoscopes and respiratory equipment.
Phenolics: Disrupt microbial membranes; found in household disinfectants.
Halogens:
o Iodine: Used for skin antisepsis.
o Chlorine: Used for water treatment.
Heavy Metals: (e.g., silver nitrate) Used in eye drops for newborns.
Surface-Active Agents: Disrupt microbial membranes (e.g., quaternary ammonium
compounds).
Dyes: Have antimicrobial activity (e.g., crystal violet).
b. Gaseous Chemical Sterilization
Formaldehyde Gas: Used for fumigating operation theaters.
Ethylene Oxide: Sterilizes heat-sensitive items like catheters and heart-lung
machines. Requires aeration due to toxicity.
Moist Heat Sterilization (Autoclaving)
1. Definition
Autoclaving uses steam under pressure to destroy all microorganisms, including bacterial
spores. It is the most common sterilization method in hospitals.
2. Principle
Steam raises the temperature above 100°C.
Moisture leads to coagulation and denaturation of microbial proteins.
Steam penetrates better and has more energy than dry heat sterilization.
3. Equipment Used
Autoclave: Sealed chamber producing steam under pressure.
Vertical Autoclave: Used in hospitals.
Horizontal Autoclave: Used in large sterilization settings.
4. Standard Parameters of Autoclaving
Temperature Pressure (psi) Time Required Use Case
121°C 15 psi 15–30 minutes General instruments
134°C 30 psi 3–5 minutes Emergency sterilization
5. Materials Sterilized Using Autoclave
Surgical instruments (forceps, scissors, clamps)
Dressing materials (gauze, bandages)
Linen (theater drapes, gowns)
Glassware (flasks, test tubes)
Rubber materials (gloves)
Certain culture media
Note: Moist heat cannot be used for heat-sensitive materials like plastics, powders, or oils.
6. Autoclaving Procedure
1. Preparation: Instruments are cleaned before loading.
2. Loading: Items placed in perforated trays or sterilization wrappers.
3. Air Removal: Essential for steam penetration.
4. Steam Generation: Steam introduced under pressure to reach the desired
temperature.
5. Sterilization Time: Maintains temperature for the required time.
6. Cooling Down: Chamber cooled before opening.
7. Storage: Sterile materials stored properly.
7. Indicators to Confirm Sterilization
Chemical Indicators: Autoclave tape changes color upon exposure to correct
temperature.
Biological Indicators: Bacillus stearothermophilus spores used for verification.
8. Advantages of Moist Heat Sterilization
✅ Highly effective against all microbes
✅ Faster than dry heat
✅ Safe for most medical instruments
✅ Cost-effective
9. Disadvantages
❌ Not suitable for moisture-sensitive or heat-sensitive items
❌ Can damage materials like plastics or powders
10. Nurse's Role in Autoclaving
Ensure instruments are cleaned before sending to sterilization.
Check sterilization indicators.
Maintain aseptic technique when handling sterile items.
Store sterile equipment properly.
