Sterilization is the process of destroying all life of microorganisms causing infection (bacteria, viruses, fungi including bacterial spores).
Disinfection: It means killing all the microorganisms (infectious agents, except spores) outside the body, by exposing them directly to the chemical or physical agents.
Commonly employed methods for sterilization are autoclaving, boiling, chemical and gas sterilization.
Autoclaving: All metal instruments are sterilized by autoclaving at a temperature of 121° celsius, at 15 pounds per square inch (Ib/sq) pressure for 30–40 minutes and rubber articles like gloves, catheters, rubber drains for 15 minutes, after the desired temperature and pressure is achieved. If sharp instruments have to be autoclaved, their sharp ends must be well-padded and covered with cotton pads to preserve their sharpness, as they lose their sharpness by repeated autoclaving.
Boiling: Metal instruments can be sterilized by boiling them for half an hour (30 minutes) which kills all the bacteria and its spores. Boiling of the instrument should be continued for half an hour after water achieves a temperature of 100° celsius. But boiling is not suitable for sharp instruments as they lose their sharpness by repeated boiling. It also leads to crust formation over the instruments.
Chemical sterilization: Sharp instruments like scissors, osteotomes, needles, etc. are sterilized by keeping them dipped in chemicals like lysol or cidex (2% glutaraldehyde solution) for a minimum of 4–24 hours (10 hours) for their proper sterilization. Fiberoptic instruments like laparoscope, cystoscope, arthroscope are sterilized by keeping them in cidex.
Direct flaming: In case of urgency, when an instrument has fallen down from the operation table and is urgently required for the ongoing surgical procedure, it can be sterilized by direct flaming. The instrument is kept in a bowl and rectified spirit is poured over it and then it is flamed. Direct flaming achieves a temperature of 1400° celsius to make the instrument sterile.
Gas sterilization: Fiberoptic instruments like laparoscope, cystoscope, arthroscope can be sterilized by keeping them in a formalin vaporizer chamber for at least 1 hour, in which formalin tablets are kept, which releases the formaldehyde gas. Chamber should be completely closed and airtight.
Note: Students can easily remember the first 4 methods of sterilization by remembering pneumonic ABCD (A: Autoclaving, B: Boiling, C: Chemical sterilization, D: Direct flaming).