Surgery and Radiology Section: Chemical

Chemical

CHEMICAL

The ethylene Oxide, a colourless highly inflammable water soluble gas, is used to sterilize the instruments which are sensitive to heat.
The plastic and rubber articles are exposed to ethylene oxide gas.
The time required for sterilization varies according to the concentration of the gas, higher the concentration shorter the time.
Heat hastens the sterilization.
65⁰c temperature and 20 to 40 percent humidity is the best.
The vacuum helps in penetration of the gas.
Rubber goods and the items which are eroded by steam like special sharp eye instruments, poly ethylene catheters, cystoscopes, stethoscope, stomach tubes, electric cords, nerve stimulator etc. can be sterilized by gas.

Formalin vapours kills spores readily. The gas is derived from the para formaldehyde tablets placed in gas tight chambers designed for sterilization of endoscopic bulbs, catheters and other delicate articles which cannot be boiled eg. Sharp instruments.
The tablets are heated with electric element (or) spirit lamp.
Sterilization for 30 minutes is sufficient to kill micro organisms and its spores.
Borax and formal dehyde solution (Borax 15g, formaldehyde, 25 ml, water 1000ml) kills ordinary micro-organisms in 30 minutes and 24 hours immersion produces complete sterility.

Beta propiolactone acts more rapidly than does either ethylene oxide (or) formaldehyde.
The disadvantage of this gas is that it may damage painted and pasted surfaces.
It has been used to sterilize hospital rooms and animal housing buildings.
It is highly toxic and carcinogenic.

Iodine is effective in aqueous and alcoholic solution. Iodine kills the micro-organisms by oxidation of their proteins.
Iodine solution kills the bacteria in one minute in absence of organic matter and 15 minute are required to kill wet bacterial spores.
Watersoluble povidone iodine is available for sterilization.

Quaternary ammonium compounds are surface active compounds and are cationic in nature.
They cause denaturation of cell proteins and inactivation of cell enzyme and disruption of cell membrane.
They are generally used in skin preparation and to preserve the sterility of the surgical instruments.
The quaternary ammonium compound which is commonly used is zephiran chloride 1:1000 solution.

The compounds in solution containing 2.5% sodium hypochlorite are effective.
These have the disadvantage of corroding metals and bleaching liner fields.
These are used for irrigation of wounds.
A 3% solution of chloride of lime (bleaching powder) in used for sterilizing utensils.
Dakin’s solution the diluted sodium hypo chloride is also used for sterilization of utensils.

They kill the micro organisms by coagulation of cell proteins (or) protein denaturation.
Phenol 1% for 5 to 10 minutes, cresol (Lysol (or) ensol) 2% for 5 minutes are commonly used.

It acts through their ionic action. Ethyl alcohol, 70% is sufficient to kill any micro-organisms.
The isopropyl alcohol is more effective, however, the alcohols do not have any action on spores.

Soaps, cetrimide and chlorhexidine are used for skin preparation.
1 % chlorhexidine and 2 % cetrimide in alcohol in combination is good for skin preparation.

The heavy metals and their salts precipitate the cell protein the rough their ions.
Bichloride of mercury 1:1000 (or) 1:2000 is used for disinfection of glass and rubber articles and thermometers.

Last modified: Wednesday, 9 May 2012, 5:46 AM