Sterilization in Hospitals

Sterilization in hospitals is one of the important process in order for prevention of hospital acquired infections, Have a look on different sturdy techniques that are used for sterilization in hospitals.

Quick revision of Sterilization

• A process by which living organisms (both viable and non-viable) are killed or removed to the extend that they are no longer detected by standard culture media which have previously been found to proliferate.
• PSI (Probability of survival per item) is the measure of sterility.
• PSI of 10^-6 indicates that One in a million packages could contain one viable microorganism after sterilization.

What are Sterilization Techniques ?

1). Steam / Autoclaving:

• It involves exposure of microorganisms to saturated steam under pressure in an autoclave achieves their destruction by the irreversible denaturation of enzymes and structural proteins.
• The temperature at which denaturation occurs varies inversely with the amount of water present. Sterilization in saturated steam thus requires precise control of time, temperature, and pressure.
• As displacement of the air by steam is unlikely to be readily achieved, the air should be evacuated from the autoclave before admission of steam. This method should be used whenever possible for aqueous preparations and for surgical dressings and medical devices.
• The recommendations for sterilization in an autoclave are 15 minutes at 121-124 °C (200 kPa).¹ The temperature should be used to control and monitor the process; the pressure is mainly used to obtain the required steam temperature.

2). Dry heat:

• Dry heat can be used to sterilize items, but as the heat takes much longer to be transferred to the organism, both the time and the temperature must usually be increased, unless forced ventilation of the hot air is used.
• The standard setting for a hot air oven is at least two hours at 160 °C (320 °F). A rapid method heats air to 190 °C (374 °F) for 6 minutes for unwrapped objects and 12 minutes for wrapped objects.
• Dry heat has the advantage that it can be used on powders and other heat-stable items that are adversely affected by steam (for instance, it does not cause rusting of steel objects).

3). Chemical (Ethylene Oxide / Other Chemicals): 

• The active agent of the gas sterilization process can be ethylene oxide or another highly volatile substance.
• The highly flammable and potentially explosive nature of such agents is a disadvantage unless they are mixed with suitable inert gases to reduce their highly toxic properties and the possibility of toxic residues remaining in treated materials.
• The whole process is difficult to control and should only be considered if no other sterilization procedure can be used. It must only be carried out under the supervision of highly skilled staff.
• The sterilizing efficiency of ethylene oxide depends on the concentration of the gas, the humidity, the time of exposure, the temperature, and the nature of the load.
• After sterilization, time should be allowed for the elimination of residual sterilizing agents and other volatile residues, which should be confirmed by specific tests.

4). Radiation:

• Sterilization of certain active ingredients, drug products, and medical devices in their final container or package may be achieved by exposure to ionizing radiation in the form of gamma radiation from a suitable radioisotopic source such as ⁶⁰Co (cobalt 60) or of electrons energized by a suitable electron accelerator. Laws and regulations for protection against radiation must be respected.

Gamma radiation and electron beams are used to effect ionization of the molecules in organisms. Mutations are thus formed in the DNA and these reactions alter replication.

• These processes are very dangerous and only well-trained and experienced staff should decide upon the desirability of their use and should ensure monitoring of the processes. Specially designed and purpose-built installations and equipment must be used.
• It is usual to select an absorbed radiation level of 25 kGy¹ (2.5 Mrad)², although other levels may be employed provided that they have been validated.

5). Plasma Sterilization:

• Plasma is basically ionized gas. When applied by an electric field, it gets ionized into electrons and ions and Voila!
• These Free radicals and ions interact with living organisms and destroys them.
• Most of the research in plasma sterilization pertains to volume discharge. Triphasic behavior was observed in these experiments. The process involves UV irradiation, photo-desorption and chemical etching.
• The spores are basically made up of simple atoms like C, O, N, H and the like. The radicals react with these atoms to form simple compounds like CO2, which can subsequently be flushed out. When the organism loses such atoms that are intrinsic to its survival, it dies.

• Phases of plasma Sterilization:

(i). Vacuum
Medical instruments are placed in the sterilization chamber (4 cubic feet in capacity). The chamber is sealed and air is pumped out to create a strong vacuum.

(ii). Injection
A solution of 59% hydrogen peroxide and water (from a cassette inserted by the operator at the beginning of every 10 cycles) is automatically injected into the sterilization chamber.

(iii). Diffusion
The solution vaporizes and diffuses throughout the chamber, surrounding the items to be sterilized. Hydrogen peroxide exhibits antimicrobial activity and is capable of inactivating microorganisms that it encounters in the sterilization chamber.

(iv). Plasma
Radio frequency (RF) energy is applied to create an electrical field, which in turn initiates the generation of the low-temperature plasma, i.e., a cloud of reactive and unstable species. These unstable particles collide with one another to produce a variety of new species, including free radicals, that, like the hydrogen peroxide vapor, are capable of inactivating any microorganisms, viruses, or spores that may be encountered within the sterilization chamber. In the plasma phase, the activated components ultimately lose their high energy and recombine to form primarily oxygen and water vapor. The combination of the diffusion pretreatment and plasma phases acts to sterilize while eliminating harmful residuals.

(v). Vent
The RF energy is turned off, the vacuum is released, and the chamber is filled with filtered air, returning it to normal atmospheric pressure. After 10 sterilization cycles, the cassette self-ejects into an internal receptacle for future disposal.

What is Sterilization workflow in Hospital ?

*Process area shown in the workflow is the area where  sterilization technique is applied. After which the sterile items are placed at sterile area for displacement to various places where they are needed.

What types of Materials are suited for each sterilization ?

*ETO – Ethylene Oxide

References and Further reading:

1. http://www.cdph.ca.gov/programs/hai/Documents/Slide-Set-13-Cleaning-Disinfection-Sterilization.pdf
2. http://www.cdph.ca.gov/programs/hai/Documents/Slide-Set-13-Cleaning-Disinfection-Sterilization.pdf
3. http://en.wikipedia.org/wiki/Sterilization_%28microbiology%29