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 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 50 0 C and not toxic like EtO.

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

ProcessLimitation 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

Processconsideration RadiationMaterials 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

ProcessMicrobe SteamBacillus stearothermophilus Dry heatBacillus subtilis var.niger GasBacillus subtilis var.niger RadiationBacillus pumilus FiltrationPseudomonus 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