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Sterilization of medical devices

The procedures in the healthcare setting involve contact of medical devices with a patient?s body. A major risk of all procedures is the introduction of pathogenic microorganisms by the medical device causing infection in the patient rather than the success of the procedure. The resulting infection not only affects the patient, further it could be transmitted to other people and the environment.

During the hospital visits we tend to observe whether the needles are new or reused, the phlebotomist is using gloves or not, the cleanliness of bed linen?

However, have you thought how clean the enterooscope or a colonoscope is?? These instruments are very sensitive to high-resolution cameras and expensive electronic circuits and not possible to use new equipment for every single patient undergoing the procedure.

Sterilization of the medical equipment is vital and is achieved by following the guidelines of the regulatory body. Different medical devices would require different levels and methods of sterilization depending on the intended use of the device and the sensitivity of the device.

Sterilization Vs Disinfection Vs Cleaning

A great majority of the people including some health professionals and media often use the terms sterilization and disinfection interchangeably though both terms convey a different meaning.

Sterilization

Sterilization is intended to communicate?categorical?meaning?- Sterile or non-sterile. However, ?people often refer to partially sterile. Emphasizing this fact, there is nothing called partially sterile! The destruction of 100% of microbes from a site or object refers to sterile while the destruction of so much as 99.9% of microbes, go into the non-sterile category.

Furthermore, another spotlight is, sterilization implies killing all forms of microbial life (bacteria and bacterial spores, virus, fungi, and parasites) rather than the destruction of just pathogens (disease-causing microbes).

Sterilization techniques

Depending on the sensitivity of the equipment, different methods of sterilization can be used such as,

  1. Wet heat sterilization
  2. Dry heat sterilization
  3. Ethylene oxide sterilization
  4. Plasma gas sterilization
  5. Ozone gas sterilization

Wet heat sterilization

The instruments should be cleaned before the sterilization.

The steam (wet heat) is produced at 121? C by the application?of pressure?inside the autoclave (equipment used for sterilization).

The?equipment is exposed to steam at 121? C for about 15 to 20 minutes. However, the opening of the autoclave after sterilization depends on the manufactures’ protocol as otherwise, steam inside the autoclave could posses a threat to the operating personnel.

Boiling should not be compared with wet heat sterilization. The boiling is achieved at 100? C which can kill most of the microorganisms but not all. The bacterial spores can survive to boil.

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Dry heat sterilization

Sterilization of the glass materials is achieved by the dry heat sterilization. In this method of sterilization, the cleaned equipment is kept inside a hot air oven at temperature 160? C for about 60 ? 90 minutes.

Ethylene oxide (ETO)

ETO is a colorless gas that’s flammable and explosive.

Sterilization by ETO is normally accomplished by the application of 10% ETO gas at 50? ?60? C for 4-6 hours followed by a prolonged period of aeration to allow the gas to diffuse out.

The four vital parameters in this method of sterilization are

  1. The concentration of the gas
  2. Temperature
  3. Relative humidity
  4. Exposure time

Varying these parameters influence the effectiveness of ETO sterilization.

An increase in gas concentration and temperature might shorten the time necessary for achieving sterilization within a specified constrain.

Gaseous?sterilization?by ethylene?oxide?was?widely used initially. However, this gas is a?mutagen?? carcinogenic.?So?this method is?widely replaced by plasma gas sterilization.

Hydrogen peroxide sterilization

In this process of sterilization, the hydrogen peroxide is vaporized by the application of microwaves or radio waves.

The resulting reactive free hydroxyl radicals produced from the decomposition of hydrogen peroxide vapors is a powerful oxidizing agent and can attack membrane lipids, DNA, and other essential cell components. It kills many bacteria and viruses. Spores are also killed after prolonged?exposure.

Depending on the concentration, process temperature, and contact time, peroxide gas is considered an effective antimicrobial, including rapid bactericidal, fungicidal, virucidal, and sporicidal activity.

The gas is safe for use on the most device and material types, including electrical components and electronics.

Medical devices and equipment that can’t withstand high temperatures and humidity, like some plastics, electrical devices, and corrosion-susceptible metal alloys, are often sterilized by hydrogen peroxide gas.

Ozone gas sterilization

Ozone gas is considered as a potent chemical for sterilization and requires high levels of humidity. The duration of sterilization by this process is approximately 4 hours.

At the end of each cycle, the ozone gas is converted back into oxygen and water vapor by passing through a catalyst before being exhausted into the room.

This ensures the safety of the operating personnel as there are no toxic emissions, no residue to aerate, and a low operating temperature avoiding the danger of an accidental burn.

The sterilization is compatible with a wide range of commonly used materials, including stainless steel, titanium, anodized aluminum, ceramic, glass, silica, PVC, Teflon,? silicone, polypropylene, polyethylene, and acrylic. However, it cannot be used on materials such as aluminum, brass, and polyurethane as well as not being able to be used to sterilize liquids, textiles, and cellulose-based materials.

Disinfection

Disinfection is relatively less lethal (destructive) to sterilization as it would not?certainly kill all forms of microbial life.?Bacterial spores are not destroyed in the disinfection process?though a few disinfectants would be able to kill spores with prolonged exposure times (3?12 hours).?Also disinfection aims to impair most recognized pathogenic microorganisms.

The process of disinfection can have three levels

  1. High-level disinfection
  2. Intermediate-level disinfection
  3. Low-level disinfection

High-level disinfection

High-level disinfection can destroy all vegetative microorganisms, mycobacterium, viruses, fungal spores, and some bacterial spores. It can achieve sterilization with sufficient contact time.

High-level disinfection can be done by

  1. By the application of heat ? pasteurization
  2. Liquid immersion ? chemical sterilants
    • 2% glutaraldehyde for 20-45 mins
    • 2 -5 % formaldehyde
    • 12% glutaraldehyde and 1.93% phenol for 20 mins
    • 1% hydrogen peroxide and 0.08% peracetic acid for 25 mins
    • 5% hydrogen peroxide for 30 min
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Pasteurizers provide thermal disinfection using heated water for 50 minutes.

Glutaraldehyde is effective against bacteria, fungi, and viruses at room temperature.

2- 5 % solution of formaldehyde heated at 60? ? 80? C to produce vapors. It is mostly used in the disinfection of rooms. The formalin gas needs to be neutralized by ammonia before using the rooms again for work as it is highly corrosive and an irritant. Although formalin is a high-level disinfectant, its application is limited by pungent fumes, a probable carcinogen.

Intermediate-level disinfection

Intermediate-level disinfection accomplishes the destruction of the viruses, mycobacteria, fungi, and vegetative bacteria (but not bacterial spores).

Low-level disinfection

Low-level disinfection can destroy vegetative bacteria (but not M.tuberculosis), some fungi, and viruses but not spores. Low-level disinfection can be achieved by the use of chlorine and phenol products for a minimum of 1 min.

Chlorine

Hypochlorites are available as liquid or solid. It has a fast-acting broad-spectrum microbicidal activity without any toxic residues. Moreover, it is inexpensive.

Phenol

Phenols are sometimes combined with detergents to form detergent germicides. However, it has a bad odor and is restricted to environmental surfaces and non-critical devices.

Alcohol

Alcohol denatures the proteins and rapidly kills the bacteria. But it is inactive against the spores. 70 ? 90%?ethanol or 90 ?95 % isopropyl alcohol is used for the disinfection of working surfaces and countertops. However, 100% alcohol is not effective, because it cannot penetrate inside the cell. Water molecules are required to transport alcohol into the bacterial cells.

Alcohols are not recommended for sterilizing medical devices and materials as they lack sporicidal (killing of spores) action and they cannot penetrate protein-rich materials.

Cleaning

Cleaning removes body materials, dust, or any other foreign material. By cleaning, not only the soil is removed, but it also reduces the number of microorganisms.

The choice of the recommended level of cleaning revolves around a lot of factors like the intended use of a medical device, the sensitivity of the equipment, available resources, and the time needed for this reprocessing. The most crucial factor is the intended use of the device.

Cleaning is done by using both enzymatic cleaners and detergents. Enzymatic cleaners are not disinfectants because they can only remove protein from surfaces. Detergents used in the cleaning of household appliances are different from the detergents used in the hospitals.

After cleaning, rinsing should be done. All the channels and lumens are flushed during each rinse followed by drying. Drying can be done by towel drying or air drying.

Moreover, the critical and semi-critical devices should be cleaned before proceeding to sterilization and disinfection?respectively?to improve the effectiveness of the process. This?allows a better contact of the disinfectant or sterilant with the surface being disinfected or cleaned. Furthermore, it will decrease the?inactivation of a chemical disinfectant and the multiplication of microorganisms.

For example, medical devices such as surgical instruments and materials used during surgery would be covered with blood, the tissue remains, chemicals, and fluids. And these materials should be cleaned at the site with proper detergent or enzyme.

Antisepsis

Antisepsis?is defined as the process of preventing?contamination of living tissue or skin with pathogenic microorganisms.

However, alcohol can be used as antiseptic and disinfectant. Alcohol is used as antisepsis skin before venipuncture.

Iodine

Iodine works by oxidizing the macromolecules of bacterial cells and destroying the organisms. It is used as a tincture of iodine plus alcohol, presently replaced with a combination of iodine and povidone (non-ionic?detergent). ?It is used for the antisepsis of skin before surgery.

Classification of medical devices

According to Earle Spaulding?s classification, medical devices are categorized into

  1. Critical devices
  2. Semi-critical devices
  3. Non-critical device

Sterilization of critical medical devices

Surgical?instruments

The surgical instruments such as forceps, scissors, surgical knives, etc should also be cleaned and then sterilized. As these instruments are metals and can withstand high temperatures, sterilization of these instruments?is?achieved by wet heat?sterilization.

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Rigid endoscope

An increasing number of diagnostic and therapeutic procedures are now being carried out endoscopes. An endoscope is an instrument that allows examination and treatment of the interior of the body canals and hollow organs.

There are two types of endoscopes ? Rigid endoscopes and flexible endoscopes.

Rigid endoscopes are used for invasive procedures, i.e. it is passed into normally sterile body cavities or it is introduced into the body through a break in the skin or mucous membrane.

Examples for rigid endoscopes are Arthroscope Laparoscope Cystoscope Bronchoscope.

Rigid endoscopes fall into the category of critical medical devices and these endoscopes need to be sterilized. Depending on the manufacturer’s instruction and sensitivity of the parts of the equipment, rigid endoscopes are sterilized by wet heat sterilization (steam) or low-temperature sterilization such as gas plasma. Automated endoscope processors (AER) are also available to sterilize the endoscopes.

Syringes and needles

Syringes and needles are important and widely used medical devices. Unlike the endoscopes and surgical instruments, syringes and needles are single-use medical devices.

However, these are single-use and disposable after the use, it should also be sterile and free of microorganisms as they are critical medical devices. These instruments should have the chance of contamination while manufacturing. Therefore, these instruments should also be sterilized following the regulatory body requirements. These equipment are sterilized mostly by low-temperature gaseous sterilization as these are heat sensitive.

Other important critical devices

Other important critical devices such as implants or prosthetics, ultrasound probes used in the sterile body cavity, cardiac and urinary catheters, etc should also be cleaned and sterilized.?This is achieved by the low-temperature gaseous sterilization.

Disinfection of?semicritical?medical devices

Respiratory equipment

Different types of respiratory equipment, anesthesia equipment are considered as semi-critical medical devices as they come in contact with the mucous membrane or body fluids. These medical devices should undergo high-level disinfection following the manufacturers’ protocol.

Flexible endoscopes

Flexible endoscopes are used for the non-invasive procedures, ie they are inserted without making a break in the body. Examples of flexible endoscopes are enteroscope (small intestine), colonoscope, etc.

High-level disinfection of flexible endoscopes is mostly achieved by glutaraldehyde disinfection preceded by cleaning.

Bedpans and urinals

Bedpans and urinals are receptables used for the toileting and urinal requirements of a bedridden patient. As many microorganisms are shed in human excretion it is important to get rid of these organisms to avoid any kind of infectious transmissions. Bedpan washers are preferred over the manual washing for the disinfection procedures.

Non-critical medical devices

Non-critical medical devices possess a relatively low risk of infectious transmission compared to the critical and semicritical devices. Non-critical medical devices including stethoscopes, pressure cuffs, etc require low-level disinfection or cleaning.

Hospital rooms and surfaces require low-level disinfection by formaldehyde or cleaning with the appropriate agent.

Gloves, specimen containers, etc are single-use non-critical devices and are disposed of after each use. However, these equipment need to be sterilized in the manufacturing unit following the requirements of the regulatory body.

Therefore, it is important to follow the guidelines of the regulatory bodies and achieve sterilization of medical devices in healthcare settings. It ensures the safety of the patients as well as the healthcare workers. Sterilization of the medical devices promises decreased chances of infection and an increased rate of success in treatments.

 

References

  1. Guideline for Disinfection and Sterilization in Healthcare Facilities (2008)
  2. Decontamination and Reprocessing of Medical Devices for Health-care Facilities

 

How clean are the medical devices - sterilization of hospital equipments

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