Surgical Sterilization Procedure

Cleaning, disinfecting and sterilising are the three levels of instrument care.

Cleaning removes dirt, debris and biological material from surgical instruments. You can clean surgical instruments manually or mechanically using water and detergents or an enzymatic cleaner.

Thoroughly clean your instruments, because debris that remains on instruments can interfere with further disinfection/sterilisation or corrupt research data. Cleaning is the first step toward sterilisation and sometimes is all that is required.

Disinfection can be broken down into three tiers: low level disinfection (LLD), intermediate level disinfection (ILD) and high level disinfection (HLD).

LLD eliminates all vegetative bacteria (except tubercle bacilli), lipid viruses, some non-lipid viruses and some fungi in less than 10 minutes. ILD destroys tubercle bacilli, mycobacteria, lipid enveloped and some non-lipid enveloped viruses and fungus spores.

In addition to killing these microorganisms, HLD can also kill bacterial spores, though not in a high number. The CDC recommends a 90 minute soak at 25°C.

Sterilisation destroys all microbial life. Some chemical sterilants can be used as HLD disinfectants when used for shorter exposure periods. Dry heat or autoclaving are the preferred method of sterilising surgical instruments.

What to Include (in the pack)

All surgical instruments and other sterile material that may be needed during the procedure should be included within the surgical pack.

This may include suture material and/or needles, gauze or cotton-tipped swabs and draping material. If pre-packaged (sterile) suture material or other equipment is used this may be aseptically placed onto the open surgical pack at the start of surgery.

Keeping the Instruments Sterile During Surgery

Use an extra piece of sterile drape material or the inside of the wrap to set instruments on when they are not in use. One of the most common errors for an inexperienced surgeon is setting instruments down on an unsterile surface.


The first step in properly cleaning your surgical instruments is to rinse off all blood, bodily fluids and tissue immediately after use. Dried soils may damage the instrument surface and make cleaning more difficult. Rinse your instruments in cool water.

Hot water can cause proteinous substances to coagulate. If desired, soak your surgical instruments in cool water with an enzymatic detergent.

The detergent helps to dissolve the proteins and break down oils. Then, the instruments may be cleaned manually or mechanically in a washer or ultrasonic bath.

Manual Cleaning

If a mechanical cleaning method is unavailable, manual cleaning may be necessary. Likewise, if instruments are easily damaged, complex (requiring disassembly) or have small lumens, they may need to be cleaned manually.

When cleaning your instruments manually, wear heavy-duty rubber gloves, a plastic apron, eye protection and a mask. Use only neutral pH detergents.

If your instruments are not rinsed properly, low pH detergents may break down the protective surface of stainless steel instruments and cause black staining.

Likewise, alkaline detergents may leave surface deposits that cause a brown stain and interfere with the smooth operation of the instrument.

Use soft plastic cleaning brushes to scrub the instruments. Do not use steel wool, wire brushes or other abrasive materials that could scratch the finish or dull your instruments. Hold the instruments below the surface of the water when you scrub them to avoid splattering contaminants.

Be sure to brush out all crevices, teeth and grooves. Rinse each instrument thoroughly under running water. Open and close hinged instruments like scissors, hemostats and needle holders under running water to thoroughly rinse detergent from the hinges.

Visually inspect your instruments to ensure they are free of stains and tissue. Check each instrument for proper function and condition. Scissors blades should be tight and should open and close smoothly. Forceps and tweezer tips should be properly aligned.

Like the scissors, the hemostats should not be loose. Verify that they lock and unlock easily. Close the needle holders and hold them up to the light. Light coming through the tip indicates that the jaws are worn. Knives and cutting blades should be sharp and free of nicks and chips.

After a visual inspection, dry the instruments with a soft cloth. This minimizes the risk of corrosion and the formation of water spots. Use a spray lubricant in the hinges to improve the function of the instrument.

Mechanical Cleaning

Typically, a washing machine runs through several cycles. A cold water rinse removes debris. Then, a hot water bath and rinse cycle is followed by a blow dry with hot air. Some washers are also disinfectors.

These units use 100°C water in the hot water cycle. Follow the manufacturer’s instructions when using a mechanical washer. Be sure to lubricate hinged instruments after the last rinse cycle and prior to sterilisation.

Ultrasonic cleaning is the most effective cleaning method, because of its cavitation. As the sound waves vibrate through the cleaning solution, they create microscopic bubbles, which grow as the pressure in the unit changes. Eventually the bubbles implode.

The bursting bubbles effectively dislodge debris, even in the most difficult to reach places. A neutral pH detergent improves the effectiveness of the cleaner, because it increases the number of bubbles.

Before you begin, fill the ultrasonic cleaner with deionised water and detergent according to the manufacturer’s directions. Run the cleaner for several minutes to allow the temperature to equilibrate and to remove any gases from the solution.

Separate instruments by metal type and process them in batches. For example, do not mix chrome plated and stainless steel instruments in the same cleaning cycle. Fully submerge all instruments. Place hinged instruments into the solution in an open position.

Make sure that any sharp instruments do not touch other instruments. Allow the instruments to process for 5–10 minutes before removing them from the ultrasonic bath and rinsing thoroughly.

As before, visually inspect each instrument, dry it with a soft cloth and lubricate any hinges.


Both thermal and chemical methods are available for HLD. As a general rule, surgical instruments are not susceptible to heat, making boiling the preferred method for disinfecting. Boiling instruments in 100°C water for at least one minute kills all microorganisms, except for a few bacterial spores. Boiling does NOT sterilise equipment.

Bring the boiler to a rolling boil. Submerge open instruments in the boiling water. When the water returns to the boiling point, turn the heat down to a gentle boil. A rolling boil could damage instruments as they bounce around in the boiler.

After one minute, remove the instruments from the water using a set of disinfected tongs. Allow the instruments to dry and lubricate the hinges. Do NOT leave boiled instruments in the water as it cools, because they could be re-contaminated. Discard the water when you finish disinfecting your instruments.

To eliminate lime buildup on boiled instruments, use distilled water for boiling or add a small amount of white vinegar to the boiler before you process your instruments.

Chemical disinfection can be used when instruments will be damaged by heat. Some chemicals that may be considered include glutaraldehyde 2% for 20 minutes, hydrogen peroxide 6%–7.5% for 20–30 minutes, peracetic acid 0.2–0.35% for 5 minutes and ortho-phthalaldehyde (OPA) for 5–12 minutes.


Sterilisation kills all microorganisms and spores. Autoclaving (saturated steam under high pressure) is the most common method for sterilising surgical instruments, however, dry heat and chemical sterilants (ethylene gas, hydrogen peroxide gas plasma, etc.) can also be used.


Prior to autoclaving, clean the instruments and lubricate all hinged instruments with a surgical instrument lubricant. Do not use WD-40® or other industrial lubricants.

Always autoclave instruments in an open position. Locking an instrument prevents the steam from reaching all the surfaces. The heat also causes the metal to expand, which can crack the hinges of locked instruments. Never overload the autoclave chamber.

Instruments can be placed in sterilisation trays or wrapped in paper or muslin before autoclaving. This helps to prevent contamination of the instruments after sterilisation.

Arrange the instruments, sterilisation trays or packs in the autoclave without stacking them. The steam must circulate freely inside the autoclave.

Follow the manufacturer’s directions for adjusting the time, temperature and pressure of the autoclave cycle. Process the instruments as follows:

Unwrapped instruments at 121°C for 20 minutes at 15 PSI above atmospheric pressure or at 134°C for 3–4 minutes at 30 PSI above atmospheric pressure

Wrapped instruments at 121°C for 30 minutes at 15 PSI above atmospheric pressure or at 134°C for 15 minutes at 30 PSI above atmospheric pressure

When the autoclaving cycle is complete and the pressure reaches zero, open the door a centimeter or two to allow the steam to escape.

Run the drying cycle as recommended by the autoclave manufacturer until all the instruments are dry. It should take about 30 minutes. Using sterile tongs, remove all the instruments, trays and packages. Allow them to cool to room temperature before storing.

Unwrapped items must be used immediately or may be stored in covered, dry, sterile trays for up to a week. Store wrapped packages in a warm, dry, closed cabinet. Instruments remain sterile as long as the wrap is dry and intact.

Dry Heat

Dry heat may also be used to sterilise surgical instruments. Instruments can be wrapped in aluminum foil or placed in sterilisation trays before putting them in the oven.

Refer to the manufacturer’s directions to heat the oven. Instruments can be heated to any of the following to be considered sterilised:

  • 180°C for 30 minutes
  • 170°C for 1 hour
  • 160°C for 2 hours
  • 149°C for 2.5 hours
  • 141°C for 3 hours

Allow the instruments to cool to room temperature inside the oven and store them as described above.

Cold Sterilisation

Soaking surgical instruments in most cold sterilants requires 10 hours to sterilise them. This can be detrimental to fine instruments. If disinfection is required (and not sterilisation) a 10–90 minute soak in a cold sterilant may be all that is required.

When using instruments with tungsten carbide inserts (needle holders, scissors, forceps), avoid using solutions with benzyl ammonium chloride.

When Do I Sterilise?

Many years ago, Earle H. Spaulding proposed a simple method to determine the level of sterilisation required for patient protection. It is still a suitable guideline for most applications today.

Spaulding categorised equipment as critical, semi-critical and non-critical.

Critical items must be sterilised, because they pose the greatest risk for infecting a patient. These include any item that enters or touches sterile tissues, the vascular system or bodily fluids like blood.

This includes surgical instruments, catheters, implantable sensors and other equipment used inside a patient.

If an item comes into contact with mucous membranes but is not used inside sterile tissues, it is considered semi-critical. Mucous membranes are not usually susceptible to a small number of bacterial spores, so a high level disinfection is suitable for semi-critical items.

These items include anaesthesia equipment, some scopes (endoscope) and temperature probes.

Non-critical items do not come into contact with mucous membranes but touch intact skin. Equipment like blood pressure cuffs, surgical beds and stereotaxic frames are considered non-critical.

They must be thoroughly cleaned, but will not require sterilisation. A low level disinfection may also be used.

Make Your Instruments Sing

With proper care and maintenance, your instruments will last for years to come. Understanding the difference between cleaning, disinfecting and sterilising can safeguard your research and protect your investment in surgical instruments, equipment and laboratory animals.

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