STERILISATION OF MEDICAL MATERIAL

TERMS & DEFINITIONS

State of sterility

The concept sterile is referred to as a state completely free of any viable microorganisms, and sterilisation is defined as the process which will destroy all viable microorganisms.

“Sterile” is an absolute term, but the assurance that any given item is sterile, i.e. free from viable microorganisms, is a probability function. The Sterility Assurance Level (SAL) is defined as the probability of a medical device being non-sterile after exposure to a validated sterilization process. The SAL defined by the norm EN 556 is 10-6, i.e. the probability of a viable organism being present after sterilization must be less than 1 per 1 million.

Sterilization batch

Items are grouped in sterilization batches (= packaging units sterilized during the same operation) to guarantee their traceability and allow the post-marketing monitoring.

Sterilization controls

These include the sterilization control (tests on the process) and the sterility control (tests on the finished product).

STANDARDS USED IN STERILIZATION OF MD

ISO 13485

Medical devices -- Quality management systems -- Requirements for regulatory purposes, Parts related to sterilization of medical devices:

  • Sterile Medical Device Clause 3.20 states that sterility requirements of each medical device can be subject to applicable regulatory requirements.
  • Contamination control (Clause 6.4.2) addresses the prevention of contamination after the devices are sterilized.
  • Particular requirements for sterile medical devices (Clause 7.5.5) sets two direct requirements:
    • Records of process parameters of sterilization of each batch
    • Traceability of all batches
  • Requirements for validation of processes for sterilization and sterile barrier systems (Clause 7.5.7)

EN 556-1

Sterilization of medical devices - Requirements for medical devices to be designated “STERILE” - Part 1: Requirements for terminally sterilized medical devices (+ AC:2006)

ISO/Technical Committee 198 : Sterilization of health care products

Scope: Standardization of processes and equipment for sterilization of health care products.

  • ISO 11135: Sterilization of health-care products -- Ethylene oxide -- Requirements for the development, validation and routine control of a sterilization process for medical devices
  • ISO 11137 set: Sterilization of health care products -- Radiation
  • ISO 11138 set: Sterilization of health care products -- Biological indicators
  • ISO 14161: Sterilization of health care products -- Biological indicators -- Guidance for the selection, use and interpretation of results
  • ISO 11139: Sterilization of health care products -- Vocabulary of terms used in sterilization and related equipment and process standards
  • ISO 11140 set: Sterilization of health care products -- Chemical indicators
  • ISO 15882: Sterilization of health care products -- Chemical indicators -- Guidance for selection, use and interpretation of results
  • ISO 11607 set: Packaging for terminally sterilized medical devices
  • ISO 11737-1: Sterilization of health care products -- Microbiological methods
  • ISO 13408 set: Aseptic processing of health care products
  • ISO 14937: Sterilization of health care products -- General requirements for characterization of a sterilizing agent and the development, validation and routine control of a sterilization process for medical devices
  • ISO 15883 set: Washer-disinfectors
  • ISO 17664: Processing of health care products -- Information to be provided by the medical device manufacturer for the processing of medical devices
  • ISO 17665 set: Sterilization of health care products -- Moist heat
  • ISO 25424: Sterilization of health care products -- Low temperature steam and formaldehyde -- Requirements for development, validation and routine control of a sterilization process for medical devices

MAIN MEDICAL STERILIZATION METHODS IN INDUSTRY

High temperature/pressure

Irradiation

Chemical

Sterilizing agent

steam

gamma or electron beam (beta) irradiation

ethylene oxide gas

Sterilizer

autoclave

industrial ioniser or irradiator

ethylene oxide autoclave, either under pressurised or over pressurised

Sterilization cycle effectiveness parameters

  • Time
  • Temperature
  • Pressure

radiation dose expressed in Mrad

  • concentration of ethylene oxide (400 to 1000 mg/l)
  • temperature (50 - 60 °C)
  • time (3 to 6 hours)
  • humidity
  • evacuation of the sterilizing agent

Characteristics

Thermal energy from steam is used to kill microorganisms by heat. Product is exposed to high temperatures (121 °C or 134°C) and high humidity.

Radiation energy produces free radicals that react with nucleic acids, damaging nuclear material or cytoplasmic structures.

EtO gas kills microorganisms via chemical reactions with nucleic acids. The process results in a temperature increase (60 °C).

A high relative humidity (50–70%) is used to allow EtO to interact with water deposited on the surface of the device.

Pressure cycling is used to alternatively pump in and evacuate EtO gas.

Only suitable for central sterilization.

Material MD

Compatible with metal devices such as surgical instruments

Not suitable for heat sensitive materials i.e. polymers.

Can change the properties of some material like plastics and have adverse effects on glues and adhesives.

Radiation has no effect on metals.

85% of the sterile MD for single use are sterilized by EtO

Can be used for heat or moisture sensitive items

More strict regulations concerning neonatology and paediatric items are under preparation in Europe.

Packaging of MDPorous packaging materials are required to allow steam to enter the package and contact the surface of the device.

Radiation can penetrate all packaging materials.

Nonporous or impervious materials such as vapor barriers and metal foil pouches can be used.

Porous packaging is required to allow EtO gas to penetrate the package and contact the surfaces of the device.
StandardsISO 17665ISO 11137ISO 11135
Validation process

Quality of steam sterilizer

Temperature profiles of product during sterilization cycles (using thermocouples)

Fractional and/or half cycles with product & B.I.s.

Dose mapping study: Dosimeters are placed in products at contract sterilizer.

Determination of product bioburden

Verification dose resistance experiment

Equipment: chamber studies with thermocouples, humidity sensors, EO concentration measurement devices.

Fractional cycles with products and biological indicators

Half & full cycles with biological indicators.

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DISINFECTION AND STERILIZATION IN THE FIELD

Disinfection and sterilization of reusable medical devices are mandatory procedures to prevent nosocomial infections (infections acquired by the patients or the medical staff in a health care facility, also called hospital-acquired infections or health care-associated infections.

Disinfection, sterilization or single use MD according to the level of infection risk

Infection risk

MD criticality

Intended use

Disinfection/Sterilization/Single use

Examples

Low

Non critical

Touches intact skin

or does not touch the patient

Low level disinfection

Tourniquet, blood pressure cuff, stethoscope, laryngoscope handle, sphygmomanometer, thermometer, standard ultrasound transducer probe…

Medium

Semi-critical

Touches mucous membranes or skin with superficial damage

Single patient use = disposable

Sterile: mucus extractor for neonate

Non sterile: oxygen mask, nasal oxygen cannula

Single use

Nasogastric tube, amniohook, examination gloves

Steam sterilization for autoclavable MD

Anaesthesia balloon, Guedel cannula, Magill forceps, laryngeal mask, vaginal speculum, biconical connector, MVA aspiration device

Intermediate level disinfection

Endovaginal ultrasound probe, vacuum extractor “Kiwi”

High

Critical

Introduced into the vascular system, body cavity or sterile tissue, regardless of the route of access

Single use MD

IV catheter, urinary catheter, IUD, tracheotomy tube, thoracic drain

Steam sterilization for thermo resistant MD

Stainless steel surgical instruments

High level disinfection for thermo sensible, immersible MD

Not a standard procedure in MSF

(For detailed procedures, please refer to ‘Disinfection and sterilization protocols for MSF projects, 2010 – updated OCP version = 2013)

! SINGLE-USE EQUIPMENT MUST NEVER BE REUSED OR RE-STERILISED !

Steam sterilization

Steam sterilization is the only recommended method for sterilization of immersible thermo-resistant MD in health care facilities. It is a reliable, simple and not toxic procedure. It requires a steam autoclave, a source of energy (electricity, fuel, gas), water with a checked or controlled quality and a basic training. All these conditions must be fulfilled, including in emergency situations.
Protocol:

  • pre-disinfection by immersion in a detergent-disinfectant solution (Anios®Clean type) for minimum 15 minutes
  • cleaning-disinfection with a detergent-disinfectant solution (Anios®Clean type) for 15 minutes
  • sterilization by steam autoclave

Important: The maximum shelf life recommended for medical devices wrapped in a double layer of sterilization paper (non-woven or crepe paper) is 2 weeks after sterilization.

High level disinfection

“High-level” disinfection concerns a very restricted number of medical devices, non-autoclavable, immersible and thermosensitive MD, likely to be reused. It consists in temporarily eliminating the vegetative forms of bacteria and viruses (but not bacterial spores) by immersion in a strong disinfectant solution.

Comment on boiling (not recommended)

Boiling for 20 minutes (+ 5 minutes / 1000 m altitude) in a recipient eliminates vegetative forms of bacteria and viruses, including hepatitis and HIV, but does not destroy bacterial spores. Boiling is not a recommended method and is only acceptable in situations where steam sterilization and “high” disinfection are impossible (e.g. traditional birth attendants in remote area).

Procedures according to the level of disinfection

level

Immersible MD

Non-immersible MD

high

• cleaning-disinfection with a detergent-disinfectant solution (type Anios Clean®) for 10 minutes and rinsing

• cleaning-disinfection with a detergent-disinfectant solution (type Anios Clean®) for 5 minutes and rinsing

• disinfection by complete immersion in a disinfectant solution (glutaraldehyde 2%) for 20 minutes, rinsing with sterile water

• drying & keep away from dust (wrap in a sterile drape)

• use maximum 24 hours after disinfection

intermediate

• immersion in a detergent-disinfectant solution (type Anios Clean®) for minimum 15 minutes

• repeat immersion for 15 minutes

• rinsing

• drying

• wiping the MD with a cloth impregnated with detergent-disinfectant (type Anios Clean®) solution

• repeat wiping

• rinsing with a moistened cloth

low

• immersion in a detergent-disinfectant solution for surfaces (type Surfanios), keep humid for at least 15 minutes

• rinsing

• drying

• wiping the MD with a cloth impregnated with detergent-disinfectant solution for surfaces (type Surfanios), keep humid for at least 15 minutes

• repeat wiping

• rinsing with a moistened cloth

Steps of steam sterilization

Step 1

COLLECTION

In a plastic container with cover

Collection consists in gathering the soiled medical devices and transporting them to the cleaning area of the sterilization unit, ensuring the safety of the staff and the environmental protection.

Step 2

PRE -DISINFECTION

Soaking in a detergent-disinfectant solution for 15 minutes

Rinsing in clean water

Pre-disinfection consists in eliminating, killing or inhibiting a part of micro-organisms by immersing the medical devices in a detergent-disinfectant solution for 15 minutes in order to reduce the number of germs.

Step 3

CLEANING - DISINFECTION

Washing and brushing in a detergent-disinfectant solution

Rinsing in clean water and drying

Cleaning – disinfection consist in removing micro-organisms and dirtiness (organic or non-organic) through the physical-chemical action of a detergent-disinfectant solution combined with the mechanical brushing and rinsing action.

Step 4

CHECKING

Visual inspection and checking of the good functioning

Preparation of sets to be sterilized

Checking consists in inspecting visually the cleanliness of the medical devices and to check their good functioning. Eliminate corroded and/or defective instruments. Open jointed instruments, lubricate the joins with silicone-free oil if necessary and wipe the surplus.

Step 5

STEAM STERILIZATION

Double packaging with sterilization paper + autoclave steam indicator tape

Sterilization at 134°C for 10 min. or 121°C for 30 min.

Sterilization with steam enables to kill all micro-organisms present on the surface of the medical devices. It is the only recommended method, whatever the health care facility. Two cycles are recommended:

134°C during 10 min. for surgical instruments

121°C during 30 min. for MD made of plastic, silicone, etc.

Step 6

STORAGE

In a clean and closed place.

Storage must preserve the sterility of the medical devices until use. The MAXIMUM recommended storage time for medical material wrapped in a double layer of sterilization paper is 2 weeks.

By “CLEAN WATER “ is meant FILTERED, non salt, low or non chlorinated water, as drinking water, tap water or rainwater if quality is controlled.