VIKIRAN

Comparison of Sterlization Process

You are aware of the advantages of the use of radiation sterlized products in reducing infection rate in surgical practice. You know a majority of disposable products can be sterilized by moist heat but also can be thru Gamma or ethylene oxide process Auto claving and EO Process require a number of parameters to be simultaneously controlled. Radiation requires only one parameter to be controlled. This makes it incariably better suited for industrial use. Authoritative sources confirm that radiation sterilization is the best method for many disposable medical products. The adjacent table lists some of the factors which influence the sterilization process.

Factor	Sterilization by
Factor	Moist Heat	Etylene Oxide	Gamma radiation
Degree of penetration	Limited	Limited	High
Temperature	x	x	P
Time	x	x	x
Pressure	x	x	P
Vacuum	x	x	P
Humidity	P	x	P
Drying/degassing after sterilization	x	x	P
Residual toxicity	Nil	^*Yes	Rare

Efficiency of a sterilization process

Efficiency of a sterilization process is measure in terms of inactivation factor which is the ratio of initial number of viable microorganisms to the number surviving offer sterilization. It follows that the higher the inactivation factor, the more efficient is the sterilization process in destroying microorganisms including pathogens, for different sterilization process area as follows :

Steam	10¹⁵ to 10²⁰
Ethylene oxide	10⁸ to 10⁹
Gamma radiation	10⁹ to 10¹⁶⁷ (for gram + ve) 10⁵⁰ to 10⁸⁶⁹ (for gram - ve)

It is thus seen that inactivation factors for common microorganisms is several orders of magnitude higher for gamma radiation. Even for pathogenic microorganisms commonly encountered in hospital environment such as Ps. Aeruginosa, Staph, Aureus, E. Coil, inactivation factor is extremely. high (10⁵⁰ to 10⁸⁶⁰) because of their high radiation sensitivity

Residual Toxicity

It is important to ensure that no toxicity inducted in the product as a result of sterilization process.

In the case of ETO, according to literature reports, the retained ETO and/ or its reaction product, Ethylene chlorohydrins (ETCH) are base-pair mutagens capable of damaging the cytoplasm and chromosomes. The permissible limits stipulated in Federal Register U.S.A. 1978 for example, for ETO, ETCH and Ehylene glycol, in ETO sterilized intrauterine device are 5, 10, and 10 parts per million (ppm) respectively. The residuals in excess of the permissible levels can cause clinical complication, such as tracheitis from endotracheal tubes or heartlung bu-pass machine, etc. which are well documented. In contrast, disposable medical products sterilized by gamma radiation cannot "retain" radiation and they do not become radioactive. This point has been carefully examined both in theory and practice. This point borne out by the fact that radiation sterilization has been accepted by health authorities the world over, as a method of choice for sterilizing medical devices. toxicity and are safe to use.

Intervenous / transfusion setd of soft PVC which have acquired a yellow tint due to irradiation but which confirm to Class II/III are undoubtedly safe for use and the colouration is in way detrimental to the use of the device i.e. Gamma Radiation.