Final disinfecting and sterilising of instruments and reusable materials

After decontaminating and cleaning, instruments and reusable material must be finally disinfected or sterilised according to the use to which they are to be put.

ANY ITEM OR MATERIAL WHICH COMES directly or indirectly INTO CONTACT WITH A STERILE PART OF THE BODY MUST BE STERILISED AND KEPT STERILE until used. That means, items which penetrate the skin and mucosa (such as needles and surgical instruments), objects that come into contact with sterile cavities (such as urinary probes, certain dressings, instruments and gloves used in surgery), objects through which flow liquids injected into the vascular system or other sterile parts of the body (such as syringes or perfusion tubes).

ANY OBJECT OR DEVICE THAT COMES INTO CONTACT WITH THE MUCOSA MUST BE STERILISED OR THOROUGHLY DISINFECTED (e.g. thermometers, otoscope ends, specula or examination gloves).

STERILISATION must be carried out either by:

- Steam sterilisation (autoclave).

This is the best method of sterilisation for all reusable materials such as syringes, needles, instruments, rubber materials, fabrics and dressings. Sterilisation is carried out either in an actual autoclave or in a presser cooker which has been adapted to take an over-pressure of one atmosphere. It must be carried out at at least 121^oC (250^oF) which is equivalent to one atmosphere over-pressure (or 1 bar or 15 psi ) for 20 minutes.

Certain autoclaves can be used on an oil or gas stove. Domestic pressure cookers may possibly be used as an alternative but then the duration has to be increased as the temperature obtained is only

about 110^oC.

- Hot-air sterilisation (in a 'Poupinel' oven).

This method is suitable for metal and heat-resistant glass instruments but it is reliable only with a good electrically heated apparatus with a thermometer in good condition (too low a temperature is ineffective and too high a temperature will ruin the instruments). Sterilisation is conducted at 160^oC for 2 hours or 170^oC for 1 hour (the duration has to be counted from the time at which the required temperature is attained).

EXTRA THOROUGH DISINFECTION can be achieved either by:

- Boiling (for 20 minutes from the time that the water reaches boiling point).

This can be done in any recipient (preferably with a lid and a perforated basket for draining the equipment after boiling).

- Steeping in one of the following solutions:

(1) The 0.1% or 1000 ppm (1 ppm = 1 part per million = 1 mg/ml = 0.001%) active chloride solution is prepared from either recently manufactured bleach (less than 3 months old) or from calcium hypochlorite, or else from sodium dichloro-isocyanurate (see the "Products for generating chlorine" instructions on page 24), account being taken of their respective chlorine content.

(2) As these products oxidise metals, the solutions are suitable only for stainless steel. Steeping should take place in a cold solution and should not exceed one half hour and must be followed by thorough rinsing in fresh water.

(3) If the instruments are to be immediately used, they need not necessarily be rinsed of chloramine T (sodium tosylchloramide) and iodised polyvidone solutions.

(4) Ethanol and isopropanol must be used at 70% (70^o) for maximum efficiency (the most concentrated solutions are the least effective). The price of these alcohols, the additional transport cost (special packaging and the fact that they are heavy) and the complex import formalities for ethanol mean that they are of limited interest.

(5) Steeping for several hours in solutions of aldehydes, formaldehyde (formol) and glutaraldehyde (Cidex(r)) will allow for thorough sterilisation (destruction of all germs) but these solutions have many disadvantages which limit their interest, i.e. thorough rinsing is essential (toxic residue), toxic vapour (formol) and very high cost (glutaraldehyde).

ATTENTION: it is to thoroughly clean equipment before sterilisation or final disinfection in such a way as to remove any residue (blood, tissue, mucus, etc.) which might otherwise hinder the process of destroying the micro-organisms.

Procedures that can be used in the field

Without electricity, the only reliable procedure for obtaining proper sterilisation is the use of an autoclave. Many medical centres, however, do not yet have autoclaves or modified pressure cookers. In this case, boiling is an acceptable alternative to sterilisation. It destroys most of the pathogenic organisms including the AIDS and hepatitis B viruses. It is simple and can be used anywhere.

Chemical disinfection can only be used as an alternative to sterilisation as a last resort and, even then, only when the proper preservation and dilution of the disinfectant can be guaranteed. Indeed, the effectiveness of chemical disinfection can be hindered by incorrect dilution, by storage in poor conditions or by the extended use of the same solution (solutions must be changed at least once a day).

Chemical disinfection should never be recommended for syringes and needles. They must be disinfected in autoclaves or boiled.