How surgical instruments are sterilized

STERILIZATION

Prior to operating surgical instruments are sent for sterilization which is a process / combination of processes in which the instruments are cleaned from all microorganisms like bacteria, viruses, fungi, etc.

Sterilization must not be confused with disinfection and sanitization because sterilization destroys all life where as the last two processes only selectively terminates the microorganisms.

Surgical instruments can be sterilized in several different ways. The three main methods used are:

    

• ETHYLENE OXIDE GAS STERILIZATION

• STEAM STERILIZATION

• RADIATION STERILIZATION

ETO gas sterilization:

In this process instruments are packed and placed in a vacuum chamber and Ethylene gas is then passed which destroys all the living organisms on the instrument. Ethylene oxide penetrates well, moving through paper, cloth, and some plastic films and is highly effective.

 Ethylene oxide sterilizers are used to process sensitive instruments which cannot be adequately sterilized by other methods. ETO can kill all known viruses, bacteria and fungi, including bacterial spores and is satisfactory for most medical materials, even with repeated use. However it is highly flammable, and requires a longer time to sterilize than any heat sterilizing treatment.

Steam sterilization:

Steam sterilization is also known as autoclaving. The instruments are placed (packed in layers of cloth) in pressure vessel and are exposed to saturated steam at 121°C for a minimum of 20 minutes. The elevated temperature and pressure destroys the cells of any living organism within the vessel.

Proper autoclave treatment will inactivate all fungi , bacteria, viruses and also bacterial spores , which can be quite resistant. It will not necessarily eliminate all prions .

Radiation sterilization:

Different radiations such as electron beam , X rays , gamma rays , or subatomic particles are used for the purpose. Radiation sterilization uses ionizing radiation to sterilize medical instruments. The radiation oxidizes any biological matter it comes into contact with, destroying its DNA, thereby sterilizing the instruments. This process is considered to be highly effective.

Other methods

Other heat methods include flaming, incineration , boiling, tyndalization, and  dry heat.

Flaming is usually used for the laboratory equipment not much for the surgical instruments.

Incineration   is done to burn the bio bastes from the Hospitals before mixing this to the nonhazardous wastes.

Boiling in water for fifteen minutes will kill most vegetative bacteria and inactivate viruses, but boiling is ineffective against prions and many bacterial and fungal spores; therefore boiling is unsuitable for sterilization. Boiling is a simple process, and is an option available to most people, requiring only water, enough heat, and a container that can withstand the heat; however, boiling can be hazardous and cumbersome.

Tyndalization  This is an up gradation of boiling process and involves boiling for a period (typically 20 minutes) at atmospheric pressure, cooling, incubating for a day,

•  again boiling, cooling, incubating for a day,
•  again boiling, cooling, incubating for a day,
•  and finally boiling again.

This is effective because many spores are stimulated to grow by the heat shock.  Tyndalization is ineffective against prions.

Dry heat is done in ovens up to a temp of 170 c for a period of 2 hrs. This process is mainly used for glass and metal objects i.e. cannot be used for plastic and rubber items.

• After sterilization all the instruments must be placed in an area free of dust, dirt, moisture etc.  as all these factors can affect the sterility.

• The shelf life of a sterilized item is also a very important factor to be considered. Any things such as  a tear in the wrapping , time elapsing, wetting  could allow the microorganisms to effect the sterilization.

How surgical instruments are made..?

Surgical instruments manufacturing is based mainly on Hand skill work. The master craftsmen spend their lives to learn the art and then produce world class instruments.

Material

First stage is the selection of material for a particular item keeping in view the required specifications. As discussed in my first post majority of the surgical instruments are manufactured from different Stainless steel grades. These grades for particular range of instruments can be found in standards like ISO 7153/1, BS 5194-4, AISI (F899).

Stainless Steel Grades

Few examples of the grades used are:

Magnetic Stainless Steels

AISI 410 /410X: Used for Gripping Instruments like Forceps, Tweezers, Dressing forceps, retractors etc.

AISI 420A : Used for Cutting instruments like Bone Rongeurs, Chisels, Gouges, scissors with carbide inserts and Needle Holders etc.

AISI 420B: Used for High grade cutting instruments like Scissors, Bone Rongeurs etc.

Non Magnetic Stainless Steel

AISI 304: Used for Cannula, Clamps, Holders, Spreaders, suction tubes etc.

Appropriate selection of the material helps in achieving the intended output of the manufacturing processes and the final required specifications.

Manufacturing Stages:

Generally following are the manufacturing stages:

Forging: This is a simply a process for shaping metal parts through compressive forces either Hot or in Cold state. There are two types of forging processes involved in surgical instruments manufacturing i.e. Hand forging for small quantities orders and Hammer Forgings for bulk quantities.

Press work: After getting a crude shape impression in a piece of metal the excess material around that shape is cut off (trimmed) to get more desirable shape in the form of forgings.

Milling: Milling is a material removal process, which can create a variety of features on a part by cutting away the unwanted material by machining. Through milling, different features such as serrations, Ratchets, Male & Female box cuttings, different types of grooves etc. are produced in surgical instruments.

Grinding / Filing: These are material removing processes using different types of grinding wheels and files. This is a very critical stage in the instruments manufacturing because here the base for the general shape is produced using different types of gauges and the initial settings are done.

Heat Treatment: Heat treatment is done to change the instruments physical and mechanical properties without changing the original shape and size like “Annealing” is done to soften the material and “Hardening” is done to Produce Hardness and “Tempering” is done to produce toughness in the instruments. Thus heat treating is a very useful process to help other manufacturing processes and also improve product performance by increasing strength or provides other desirable characteristics

Chemical Treatment: The main purpose of chemical treatment is to clean the surface of the steel parts and if carried out properly, they all increase the corrosion resistance.The main processes used in the surgical instruments manufacturing includes:

• Pickling

It is usually done after the heat treatment process to remove the scale formed because of oxidation. Dilute Sulfuric Acid / Nitric Acid is used for this purpose.

• Passivation

The passivation is performed when free iron, oxide scale, rust, iron particles, metal chips adversely affect the stability of the surface.
Passivation consists of immersing stainless steel instruments in a solution of nitric or citric acid and sodium dichromate, dissolving the imbedded iron particles and restoring the original corrosion-resistant surface by forming a thin, transparent oxide film.

• Electro polishing

Passivation also is accomplished by electro polishing. Electro polishing is an electrochemical process that is a super passivator of stainless steel and results in a more passive surface than the other methods mentioned above.

The metal, which is electro polished gives a bright surface and appearance of metal looks fine. The second advantage is that some burr is also removed in this process. Most commonly phosphoric and sulphuric acids are used in conjunction with a high current density to clean and smooth (by metal removal) the surface of the steel.

Fixing: At this stage setting is done to align the instruments with proper functioning.

Polishing /Buffing : These are the metal finishing processes to produce different types of appearances like mirror or dull. Different abrasives are used on a work wheel to finalize the finish.

Checking/ Packing:  The instruments are checked for desired specifications and sent for final inspection and testing before packing.

What are surgical instruments…?

So what are these….? Simply “These are the tools used by a Surgeon during operation, examination etc.”

For every part of a human body there are specially designed instruments which are used such as ophthalmic instruments used in Eye surgery, cardiovascular instruments use in heart surgery, Skin instruments, Kidney instruments etc.

Surgical Instruments are also categorized as single use and reusable.

Those instruments which are marked as single use  (encircled 2 with a crossing line) are usually sterilized packed and can only be used once where as reusable instruments can be used again and again after sterilization, provided their maintenance is carried out as per standard procedure.

History

Archeologist found different objects such as bones , bamboo , stones in the crude instruments form from the period around 10,000 B.C  which were used for medical purposes at that time.

More sophisticated tools were found in the late Bronze and Iron ages and the early Egyptian civilization. These tools were far more superior function wise as compared to the stone ages tools and showed us a continued improvement in the designs fulfilling the human needs.

In the middle Ages and the Renaissance surgical instrument development continued in Europe and a whole range of instruments used exclusively for surgery emerged.

Surgical Instruments can be broadly categorized as follows:

•      Cutting Instruments: those with a cutting edge such as saws, knives,    some of these requiring Grips / handles.
•       Gripping instruments such as  , Thumb Dressings , Tweezers, Spatulas

·                Paired items like Forceps, Scissors , Rongeurs .

Production simply starts with Forging, then machining followed by some filing , Grinding  and Polishing .

From the 17th century to the 19th century, new studies and research in the surgery field led to the development of more sophisticated tools with specialized functions to be used on different parts of human bodies.

In the 20^th century people started using stainless steel for manufacturing surgical instruments because of its properties such as corrosion resistance, hardness, formability, long life and till present stainless steel is considered to be the most suitable material for majority of the instruments etc.

Recent development includes the use of other material like titanium ,Silver alloys, Laser guided instruments and micro surgery instruments.