Sterilization of Medical Devices: Bodhisatwa Das

Sterilization refers to any process that effectively kills or eliminates transmissible agents (such as fungi, bacteria, viruses, spore forms, etc.) from a surface, equipment, article of food or medication, or biological culture medium.Sterilization does not, however, remove prions. Sterilization can be achieved through application of heat, chemicals, irradiation, high pressure or filtration.

Moist Heat Dry Heat Ionizing Radiation (Gamma and E-beam) UV Light Ultrasound Ethylene Oxide (EO) Hydrogen Peroxide Gas Plasma Filtration

Commonly 1210 C and 15 psi gauge pressure applied saturated steam of an autoclave.

Works by oxidizing and denaturing enzymes.

The proper time and temperature for Dry-Heat sterilization is 320°F (160°C) for 2 hours or 340°F (170°C) for 1 hour.

Dry-heat destroys microorganisms by causing coagulation of proteins.

Mainly works by DNA double strand break. Commonly it produce free radicals that

attack cellular DNA.

Commonly destruction is done by DNA damage. It is used in workstations like laminar air flow.

Ultrasound in liquids causes gas bubbles to form and then often collapse violently.

This cause microbes to be killed.

Alkylates proteins and DNA and hence induce point mutation and DNA damage.

It should be done after a drying process.

Oxidizes the cell membrane or produces nascent oxygen that reacts with DNA to kill the pathogen.

It is less hazardous than ethylene oxide.

It works together by UV photon and free radicals.

It operates at 500 C and not toxic like EtO.

It is done by Microfilters or HEPA filters. Mostly the pore size of the filter determines

its efficiency.

Process Limitation

Steam •Batch process•Few polymer-based devices work.• Packaging aesthetics not great .

E-Beam •Lower penetration and density limited.•Not in house process for small companies.•Some materials remain unsuitable.

EtO •Penetration sometimes difficult•Residuals•Batch process•Long process and release time

Gamma •More expensive than EO•Not in-house process•PTFE and acetal difficult•Yellowing and embrittlement of some polymers

Process consideration

Radiation Materials compatible with dose needed for sterilization without embrittlement or other physical problem.

Steam •Must allow sterilant in and be breathable during cycle•Must remain aesthetically acceptable•Must allow efficient heat transfer•Seals must withstand temp, pressure, and moisture ranges during cycle

EtO •Must allow sterilant in and be breathable during cycle•Must remain aesthetically acceptable•Must allow gas elution during aeration•Seals must withstand temperature, pressure, and moisture ranges during cycle

D value:The time required at a certain temperature to kill 90% of the organisms being studied.

Factors Affecting D value: Temperature Relative humidity pH Initial bioburden Presence of biological tissue.

Physical Indicators(Temperature, Pressure) Bio-Indicators

Process Microbe

Steam Bacillus stearothermophilus

Dry heat Bacillus subtilis var.niger

Gas Bacillus subtilis var.niger

Radiation Bacillus pumilus

Filtration Pseudomonus diminuta

EtO should not leak. EtO should not be used in moist

environment. Autoclave has to be operate properly,

pressure measurement should be done properly.

Regular Dose measurement has to be done in radiation work station.

Radiation leakage has to be avoided.

WHO Recommendations Annex III(For reprocessing CJD contaminated instruments)

Disposable Instruments: Incinerate (and all instruments exposed to high infectivity tissues.)

Heat Resistant Instruments:

◦ Immerse in 1N NaOH

◦ Heat in a gravity displacement autoclave at 121°C for 30 min, or 132º C for 3-5 min

◦ Rinse in water

◦ Routine sterilization process