STERILIZATION TECHNIQUES

DRY HEAT STERILIZATION: 

​This technique is best suited for sterilization of surgical, suture and birth instruments. It uses thermal conduction for sterilization.

METHOD:
In this technique, heat is absorbed and passed through layers. First, it is incorporated in the outer layer and then transferred to the next layer. When the temperature reaches its maximum, the particular item is said to be sterilized. Dry heat destroys proteins. Proteins are the essential component of a microorganism’s cell wall, and hence their death occurs after the removal of proteins. It usually takes a longer time than steam sterilization, because moisture penetrates faster than dry heat and causes the death of microorganisms

PROCEDURE:

1. Preheat oven (with internal oven thermometer to verify correct temp)
2. 320’ F for 2 hours OR 340’ F for 1 hour
3. Clean, dry and package metal instruments
4. Place instruments plastic side up, on a towel or paper bag on a cookie sheet or bake stone
5. Set timer for appropriate time based on temp

DISADVANTAGES:

1. High temperature i.e. 160-170 degree Celsius is required.
2. Items such as plastic and rubber cannot be sterilized because of increased temperature requirements.
3. Slow heat penetration- an hour or two of heat- plus cool down time is required.
4. Requires oven and a constant source of electricity.

STEAM STERILIZATION VIA AUTOCLAVE:

For steam sterilization an autoclave is used. An autoclave is an instrument in which saturated steam is applied under pressure. Destruction of microorganisms occurs by the irreversible denaturation of enzymes and structural proteins. Like dry heat sterilization, it can also penetrate through all the surfaces of the instrument but is not time-consuming. This technique provides complete sterilization in a shorter time period.

PROCEDURE:

1. Fill autoclave with distilled water according to package instructions
2. Clean, dry and package metal instruments
3. Place instruments plastic side up on rack
4. Secure autoclave door according to package instructions
5. Set timer or turn on self-timed autoclave to the appropriate time
6. Be sure to properly vent autoclave before opening

DISADVANTAGES:

1. Moisture retention in package is possible.
2. Only stainless steel and plastic items can be used for this technique.
3. Danger exists when not following autoclave instructions.​​

STEAM STERILIZATION VIA PRESSURE COOKER:

​Pressure Cookers, or pressure canners, are often referred to as portable autoclaves. While this is not entirely true, the pressure cooker can be used to create much of the same effect. Using an immersion only method, pressure cookers are ideal for sturdier instruments and most substrates. While they cannot reach quite the level of pressure and heat that an autoclave can, pressure cookers have proven themselves time and time again as an effective means of sterilization. 

Because it is not designed to create a vacuum as its first priority, however, it is recommended that you let it vent and build pressure for a bit before starting your timer in order to create complete sterilization.

For more in-depth explanation of the comparisons of different brands please see this thorough study.

PROCEDURE:

1. Read your pressure cookers instructions
2. Add clean instruments to the proper amount of water bath
3. Close lid and turn on burner
4. Process instruments  at 15 psi for at least 15 min. This means the temp will be about 121 °C within the cooker.

DISADVANTAGES:

1. Sterilization time required can vary depending on the amount of liquid the size of the pressure cooker and the altitude 
2. It can be messy and time consuming
3. Danger exists if not following instructions
4. Moisture retention in package is possible.
5. Only stainless steel and plastic items can be used for this technique.

CHEMICAL STERILIZATION:

If as a result of dry heat or steam heat sterilization the instruments are at risk of being damaged or if the autoclave or oven eclectic source is not available, then the best technique to sterilize the instrument is chemical sterilization. Most commonly formaldehyde and glutaraldehyde are used as disinfectants. By using high-level disinfectants, bacterial endospores can be killed if exposed for 10-24 hours. Sterilization usually takes place when you soak the item in 2-4% glutaraldehydes, for at least 24 hours and in 8% formaldehyde for at least 24 hours. Both disinfectants require special handling because the residue may leave after the complete procedure; rinsing with sterile water is essential. 

PROCEDURE:

1. Purchase chemical items, read package insert carefully to avoid injury or exposure
2. Clean, and dry instruments
3. Place instruments and chemical liquid into container that completely covers all instruments
4. Leave for 24 hours in a safe and secure location
5. Remove just before use using sterile technique

DISADVANTAGES:

1. Skin irritation is possible.
2. Chances of leftover residues.
3. Rinsing with sterile water after soaking requires heat to create sterile water.
4. Glutaraldehyde is expensive.

GAS STERILIZATION:

Ethylene oxide or any other highly volatile substances are the active agents to this technique. Must be mixed with any other inert gas, to reduce highly toxic properties. This technique can only be used when no other method works. The efficiency of this gas depends on the concentration of gas, humidity and time exposure. Because 100% EO is required and it is extremely volatile, this procedure must take place in a vacuum. This is not a viable technique for community-based midwives

DISADVANTAGES:

1. Time-consuming (24-72 hour process).
2. Difficult to control.
3. Highly skilled staff supervision is necessary throughout.
4. Maintaining sufficient humidity during procedures is essential.
5. Expensive equipment necessary

A NOTE ON BOILING INSTRUMENTS:

Boiling instruments in 100°C water for at least one minute kills 99% microorganisms, except for a few bacterial spores. Boiling does NOT sterilize equipment. This is a disinfection method and may be deemed to be acceptable for cord clamping and cutting implements, but is not recommended for episiotomy scissors or suturing instruments. Pathogenic organisms begin to die off between 60° C and 70°C. To fully disinfect, water must be at a full rolling boil for at least 2 minutes at sea level, 3 min at 6000 ft or above to achieve full disinfection, with instruments submerged the entire time.