Application Note – Sterilization N.4

Standards for  sterilization of  “medical devices”

Application Note – Sterilization N.3

Good Sterilization Practice

Introduction

Sterilization by steam autoclaving is not correctly performed if only time and temperature parameters are considered. The following notes has the purpose to help the staff to perform a correct sterilization cycle.

1. Air trapping. Steam displaces air downward. Therefore, long, thin containers should not be placed in the autoclave in an upright position. Sterilization of materials in plastic bags will likewise fail, unless the bags are wide open and only partly filled to allow access of steam and escape of air.
2. Heat penetration. A cold object placed in an autoclave takes time (over and above the time it takes for the chamber to reach sterilizing temperature) to heat adequately.  For example, a 1 liter container of fluid must be autoclaved for 25 minutes after the chamber reaches 121°C, but a 4-liter container may require an hour for sterilization.
3. Contact with steam or water. Dry microorganisms protected from contact with steam (for example, with oil, plastic wrappings, or containers of talcum powder) cannot reliably be killed by autoclaving.
4. Heat indicators. Test tubes and tapes containing a heat-sensitive chemical indicator are often included along with objects when they are autoclaved. The indicator changes color during the autoclaving and thus gives a visual means of checking whether the objects have been subjected to adequate heat. A changed indicator does not always indicate that the object is sterile, because heating may not have been uniform, and even stored wrapped objects may have organisms reintroduced (see No. 7). Tubes or envelopes containing large numbers of heat-resistant spores of the nonpathogenic bacterium Bacillus stearothermophilus, which acts as a biological indicator, are also frequently included with packs of materials being autoclaved.  Death of these spores indicates adequate killing at the point where the tube or envelope was placed, which should be near the center of the material being autoclaved.
5. Elevated boiling points under pressure. Fluids in autoclaves are prevented from boiling, even though well above their normal boiling point, by the elevated pressure. If at the end of the period of autoclaving, valves are opened to release the pressure, these fluids will immediately boil and may even explode their containers. The pressure must be maintained to prevent boiling until the temperature has dropped below the boiling point at atmospheric pressure.
6. Negative effects of heat on some materials. Most autoclaves can be adjusted to operate at temperatures lower than 121°C, the usual autoclaving temperature. The use of’ lower temperatures is satisfactory for materials that can be tested for successful sterilization before being used. For example, certain heat-sensitive bacteriological media are sterilized at 115°C. This temperature is usually effective because heat-resistant microbial contaminants are rarely present in the media. Moreover, samples of the autoclaved media are easily tested for sterility before being used.
7. Prevention of recontamination. Objects to be autoclaved are usually wrapped in paper or cloth to allow penetration of steam during sterilization and to prevent recontamination thereafter. When wet, these coverings are readily permeable to bacteria and should therefore be allowed to dry before removal from the autoclave chamber. After that they should be stored in a closed cupboard or drawer to prevent the reintroduction of contaminants by ants, moths, or other means.

Font: E. Nester, E. Roberts, M. Lidstrom, N. Pearsall, M. Nester: Practical Aspects of Autoclave Use – Microbiology,  Saunders College Publishing. pg 802-803.

Application Note – Sterilization N.2

Preparation of material before sterilization

Introduction

All the material to be sterilized must be free from all residual matter (e.g.: blood, organic tissue, mineral deposits, etc.), and should also be dry.

Cleaning

1. The instruments (e.g.: surgical tools) should be cleaned as soon as possible after their use. Ultrasonic bath can be used.
2. Rinse the instrument after cleaning.

Instrument preparation

Final cleaning and lubrication (if requested) according to the instrument manufacturer’s.

The instruments should be bagged or introduced in plastic or metal container that allow steam penetration.

The plastic bags never should be in contact with the heating element on the bottom.

Sterilization

• Read the suggestion/information of the manufacturer for proper sterilization temperature and time.
• Insert a sterilization chemical indicator in each try or inside each wrapped pack.
• The biological indicator should be used weekly/monthly according to the available specific  Standard Operating Procedure (SOP). The “spore test” should be positioned in the areas that are most difficult for the steam to reach.
• Be sure that all instruments remain separated during the sterilization cycle to guarantee a free access/circulation of the steam. Do not overload the autoclave chamber and the trays/basket because overloading will produce not correct sterilization and drying cycles. 
• Empty container/canister should be placed inside the autoclave upside-down to prevent accumulation of water.
• The autoclave must be opened, at the end of the sterilization cycle, only at the temperature indicated by the manufacture.

Application Note – Sterilization N.1

Good Steam Sterilization Practice

Introduction

The bigger number of accidents in the analytical laboratory is due to the non application of the basic safety rules. Only trained and specifically educated operator should use the autoclave sterilizer.

The basic autoclave safety rules

It is imperative to strictly follow the suggestions reported in this document.

1. It is forbidden to remove any of the safety devices of the autoclave.
2. The material to be sterilized should compatible with the programmed sterilization cycle and only products  that are intrinsically safe should be sterilized (e.g.: possibility of explosion).
3. The temperature and the pressure indicated on the display must be always monitored and evaluated before to take any action.
4. The flexible thermo-probe must be positioned  inside the container (vial / bottle / Erlenmeyer flask / carboy, etc.) to be sure the monitored temperature is the temperature of the liquid to be sterilized and not the temperature of the sterilization chamber. If the flexible thermo-probe is not available, and it is fixed on the wall of the autoclave, it is necessary to consider that the temperature of the liquid reached inside the container will be always late. This retard will be proportional to the volume of liquid. If, for example, the volume of the liquid is 50 ml, it is necessary to consider at least a margin of 30°C and therefore the cooling  should reach about 40°C (considering 65-70°C are safe) before to open the autoclave.
5. In any case, if the flexible thermo-probe is fixed inside the liquid of a glass container, there is the risk of a breakage. In this case the temperature is the temperature of the sterilization chamber!
6. It is advisable, when possible, to open the autoclave when the temperature of the sterilization chamber is at room temperature.
7. Face shield and protective gloves should be positioned very close to he autoclave and used each time the  autoclave is open at the end of the sterilization cycle.

The Standard Operative Procedure (SOP)

A specific Standard Operative Procedure (POS) about the “Good Autoclave Practice” should includes all the reported instructions/suggestions.