|Minor Surgical Procedures in Remote Areas (MSF, 1989, 172 p.)|
· Sterilization = elimination of all micro-organisms (viruses, microscopic fungi, bacteria, both vegetative and spore forms).
· Disinfection = elimination of most micro-organisms present on a surface or object.
· Decontamination = disinfection of object soiled by infectious material (pus, blood, excrete, etc.).
All equipment or supplies:
· coming into contact with sterile parts of the body (injection equipment, surgical instruments, some dressings, catheters.).
· used for perfusion. should be sterilized and kept sterile until utilization.
All reusable items, which do not correspond to the above definition, but which come into contact with mucus membranes, or get soiled with pus, blood, lymphatic or vaginal secretions, should be sterilized or subjected to a high level disinfection (effective among others against HIV and hepatitis B virus).
All soiled, non reusable equipment should be incinerated (warning: never recap needles after use = main cause of accidental needlestick).
To carry out proper sterilization is not always easy in the field conditions of isolated rural medical centers. It requires proper appliances (autoclave, hot air sterilizer), and an energy source.
In practice, one is often obliged to use alternative procedures which are not wholly satisfactory as they produce disinfection rather than sterilization (They are however compulsory if one cannot do better) (see following chapters).
Disinfection and sterilization of medical equipment is not enough to prevent iatrogenic infections (resulting from medical practice). It is obvious that basic hygienic and asepsis techniques ought to be applied: cleaning and disinfection of surfaces and premises, personal hygiene of the staff, aseptic handling of sterilized instruments, etc.
Cleaning of reusable equipment
Soiled items and instruments should be carefully cleaned before being sterilized or subjected to a final disinfection.
The presence of organic matter could protect germs against the action of a disinfectant or sterilizing agent, or could react against it, rendering it ineffective.
Cleaning can be done either with water alone, with water and soap (or detergent), or with water and a compound of disinfectant/detergent.
Cleaning with a disinfectant chemical aims mainly to reduce the risks of contamination for the staff, but it does not eliminate them completely.
The staff in charge of instrument cleaning should be aware of the contamination risks (AIDS, hepatitis B), they should wear thick plastic or rubber gloves, and be careful when they handle sharp instruments.
After use and before cleaning, all instruments and items should be soaked in water to avoid deposits drying up. A disinfectant could be added for a first decontamination (chloramine 20 g/1, lysol 50 g/1).
Metallic instruments can be damaged if they are left in water too long (over several hours) or if the disinfectant concentration is too high.
Needles and syringes for immunization should be soaked and cleaned with water alone, as traces of soap and disinfectant can inactivate vaccines.
After cleaning, instruments and items should be rinsed thoroughly with water and dried, then sterilized, boiled or disinfected (with a high level disinfectant) depending on their use and the local sterilizing facilities.
Linen and dressing
To decontaminate linen and dressings, one should wash them with an ordinary washing powder (eg. OMO) and boil them if possible (5 minutes).
If boiling is not possible, linen should be washed, rinsed and soaked for 30 minutes, in a 0.1 % chlorine solution (hypochlorite, bleach, chloramine), or 5 % lysol solution. It should then be rinsed abundantly and dried.
Theatre linen should be sterilized in an autoclave or ironed depending on local facilities.
Sterilization methods and alternatives
Sterilisation by steam under pressure in an autoclave.
Autoclaving is the most reliable sterilization method and the only one that allows effective sterilization of all medical equipment and supplies (especially linen and rubber). But relatively sophisticated appliances and energy source (electricity, kerosene or gas) are needed.
It is based on the same principle as a kitchen pressure cooker. Because water is heated in a closed container, temperatures above 100°C can be reached.
In the absence of air (air is purged at the beginning of sterilization), the temperature can be regulated by controlling the pressure.
According to the type of supply to be sterilized, sterilisation is carried out at 121°C (1 atmosphere over atmospheric pressure) or at 134°C (2 atm. over atmospheric pressure).
· Do not forget to expell air (purge) while increasing the pressure (otherwise the temperature in the autoclave will not be sufficient).
· Drums or boxes holding objects to be sterilized must be open, never closed (unless fenestrated). The sliding windows in the special autoclave boxes should also be open during sterilization.
· Count the sterilizing time from the moment the required temperature or pressure is reached, not from the start of the heating phase.
Dry heat (in hot air sterilizer or oven - called a Poupinel in french)
Sterilization by hot air (dry heat) at 160°C (320°F) for 2 hours or at 170°C (340°F) for 1 hour.
Reliable method provided it is carried out in a good electric appliance with working thermometer (an air circulation device is needed in large ovens).
This method is convenient for metal, heat resistant glass, and vaseline, but is not convenient for linen or gauze swabs. The oven method is quite simple but consumes more energy than an autoclave.
Ovens heated by charcoal fires or kerosene heaters are not reliable because they do not produce a sufficiently high temperature.
Time should be calculated from the moment the required temperature is reached (this is very important).
· Begin heating with the door open to expel any humidity (which could rust instruments).
· Do not exceed 170°C (could damage metallic instruments).
· It is better to place items in dosed boxes. However, large boxes should be left half-open to allow the material to more rapidly achieve the correct temperature.
Boiling for 20 min (adding 5 minutes for 1000 altitude) provides high level disinfection, but not sterilization because it does not destroy bacterial spores (eg.: tetanus, gangrene).
Boiling is nevertheless essential when autoclaving or hot air sterilization are not possible. It is particulary useful for needles and syringes (it destroys HIV and hepatitis B virus).
After needles and syringes have been boiled, they should be kept dry and not left in the water (which can easily become recontaminated).
· In a flame: Effective if instruments are made red hot. This method should only be used in exceptional circumstances as it damages metal.
· With alcohol: Instruments are dipped in alcohol and set alight. This method is unreliable, expensive and in the long term damages instruments.
Surgical drapes and gauzes can be ironed if an autoclave is either unavailable or too small to hold large operating drapes.
Iron on a table or bench covered with a sheet that has itself just been "sterilized" by ironing.
Dampen each item slightly with filtered boiled water.
The iron should be very hot and passed several times over each side of linen/gauze.
However, if it is available, autodaving is always the preferred method.
Immersion in "high level" disinfectants
Immersion (of clean equipment) in the following disinfectant solutions destroys bacteria and virus including HIV and hepatitis B virus. The bacterial spores are generally not destroyed.
This process could be used as an alternative to sterilization when autoclaving or hot air sterilization are not possible.
Boiling however is always preferred. The effectiveness of chemical disinfection can always be impaired by dilution errors, by bad storage conditions, or by prolonged utilization of the same solution (solutions should be renewed at least once a day).
Chemical disinfection should never be recommended for syringes and needles.
1. Hypochlorite solution (0.1 % or 1,000 ppm - 1ppm = 1part per million = 1mg/ml = 0.0001% - available chlorine) is prepared either from liquid bleach recently manufactured (< 3 months) or from calcium hypochlorite or from sodium dichloroisocyanurate (NaDCC, "Javel tablets", Javel solid, Stafilex, Actisan.), diluted according their respective available chlorine content.
Fresh liquid bleaches contain 3 to 15 % available chlorine (sometimes expressed in chlorometric degrees, 1° chlorom. = approx. 0.3 % available chlorine). Calcium hypochlorite contents from 30 to 70 % available chlorine.
The NaDCC based tablets content generally 1.5 g available chlorine per tablet (1 tablet per litre = 1,500 ppm available chlorine). NaDCC withstands heat much better than bleach and calcium hypochlorite.
2. As hypochlorite solutions are corrosive for metal, these solutions are convenient only for good quality stainless steel. The soaking should not exceed 1/2 hour and should be followed by thorough rinsing.
3. If instruments are used immediately after soaking, it is not necessary to rinse the chloramine or the polyvidone iodine solution.
4. Ethanol and isopropylic alcohol (isopropanol) should be used at 70 % (70°) for the best effectiveness (more concentrated solutions are less effective). The prices, transportation and importation problems limit the use of these alcohols.
5. Immersion for several hours in aldehyde solutions, formaldehyde (formalin) and glutaraldehyde (Cidex), provides proper sterilization (destruction of all germs). These solutions however have many disadvantages: thorough rinsing compulsory (toxic residues), toxic vapours (formalin), high cost (glutaraldehyde).
· In order to obtain effective disinfection, equipment must be cleaned before immersion in all these solutions.
· Aqueous solutions of cetrimide (Cetavlon), chlorhexidine (Hibitane), Savlon, HAC, Dettol and other common detergent and disinfectant solutions do not provide sufficient disinfection.
Soaking instruments in these solutions with the aim of "sterilization" should be avoided. This only provides an illusive feeling of safety and could in fact be a source of contamination.
· Ethylene oxide
This method cannot be considered in field conditions because of its cost and of the special installation it requires (ethylene oxide is very toxic).
· Formol vapour (paraformaldehyde or trioxymethylene or "formol " tablets and Aldhylene)
Formol autoclaving also cannot be considered in the field. However formol vapour is often used for "makeshift" sterilization of instruments. The instruments are thoroughly cleaned and dried, then placed in a airtight container for at least 24 hours (minimum temperature of 20°C), either along with formol tablets (5 tablets for 1 litre container), or with formol alcoholic solution (Aldhylene) (1 ml for 1 litre container). Afterwards instruments are rinsed with sterile water. This is often impracticable, but it is absolutely compulsory if there is any visible deposit.
Users should be cautious during manipulation as vapors are toxic and highly irritative.
This method is not suitable for linen or gauze swabs as they absorb formaldehyde, which is toxic and necroses skin and mucus membranes.
This method is not totally reliable and has many disadvantages. It should be abandoned. If it is used an effective disinfection method against HIV (AIDS virus) (eg. boiling) should always be carried out before hand.
Equipment and methods recommended Dispensaries
· 1 small autoclave pressure cooker type (volume 15 to 20 litres)
· 1 powerful kerosene stove (or electric hot-plate)
· 1 metal mesh basket
· Appropriate fenestrated containers (drums)
· Instruments, syringes, glass, rubber, plastic, gauze swabs, small drapes: autoclave.
· Large drapes, gowns: wash with soap powder, boil if possible, then "sterilize" by ironing.
If possible same equipment as for dispensaries.
· 1 container for boiling
· Chloramine T or Polyvidone iodine (Betadine)
· Formol tablets or Aldhylene (for exceptional use)
As for dispensaries if possible.
· Metal instruments: boiling (best), otherwise sodium dichloroisocyanurate (NaDCC) or chloramine T or polyvidone iodine (exceptionally, after boiling and drying, instruments may be kept with formol tablet or Aldhylene until utilization)
· Needles, syringes: boiling
· Swabs: use disposable supplies
Hospitals with surgical facilities
Same equipment as for dispensaries and:
· 1 large autoclave (interior dimensions about 40 x 60 cm), operating with electricity, gas or kerosene according to local conditions.
· 2 mesh baskets
· Several fenestrated drums (number according to activity)
· Several fenestrated instrument boxes
If electric current is available continuously for at least 3 hours per day:
· 1 electric hot air sterilizer
· Metal instruments, glass: hot air sterilizer if good electric apparatus available, other-wise autoclave
· Swabs, linen (gowns, drapes.): large autoclave
· Rubber, plastic items, syringes: small or large autoclave (at 121°)
Directions for use of an autolcave
In small autoclave, pressure cooker type, there is no purging tape, one uses the valve for purging.
The safety valve should not be manipulated during autoclaving (it will function only in case of excessive pressure rise).
Pressure gauge shows a pressure scale and sometimes a temperature scale. Pressure could be indicated in different manners.
One may consider that 1 bar = 1 kg/cm² = 1 atmosphere = 15 psi
Temperature could be indicated in °C ou °F (135°C = 275°F; 121°C = 250°F).
1. Put the require quantity of water in the autoclave before each sterilization (dry heating could damage the autoclave): the level is usually marked or the quantity indicated by the manufacturer. If possible use distilled water or filtered rain water.
2. Place the objects to be sterilized in the mesh basket or onto the support, leaving enough room for vapour to circulate freely. The sliding "windows" on drums or containers must be open. Do not overload the autoclave.
3. Close the lid by tightening the bolds in diametrically opposite pairs (as the wheel nuts of a vehicle).
4. With the purging tap or valve open, begin to heat.
5. When a continuous jet of vapour is coming out of this tap/valve, close it.
6. Allow the pressure to rise to 0.5 atm, then open the purge tap/valve for 10 seconds to purge air, then close it.
7. Repeat this purge at about 0.7 atm, then again at about 0.9 atm. After this, all air should have been expelled from the autoclave and only steam will remain.
8. When desired operating pressure (and thus temperature) is obtained, sterilization begins. Start to time it then, not before.
The pressure valve regulates the pressure inside the autoclave allowing excess steam escape. There may be two interchangeable valves or positions to operate at either 1 or 2 atm. If a lot of steam is being expelled, heat source should be lowered slightly.
9. After the required duration of sterilization, shut off the heat source.
10. Evacuate water and steam:
· For large autoclaves: through drain tap (to be connected outside).
· For pressure cooker type autoclaves: evacuate the steam by opening the purge valve. Once pressure drops to zero, open the lid, lift out the basket, pour out the water then replace the basket.
11. Allow to cool with the lid slightly open. Residual heat helps dry the sterilized items (the danger of contamination by ambient air is minimal).
12. Once items are dry, close the sliding windows on drums.
If the autoclave is equipped with a drying system, follow the
manufacturer's recommendations starting from paragraph 9.
(See table 8).
· The stove should be powerful! enough to obtain a minimum rise of pressure of 1 atmosphere (1 bar or 1 kg/cm² or 15 Psi).
· If possible, use sterilization autoclave tests, for example, 3M Autoclave Tape should turn black, brown is insufficient). Warning, do not confuse test tape for hot air sterilizers with that for autoclaves. They are very similar but not interchangeable.
Place tests (eg. strip of tape) in the middle of the load into the boxes or drums to ensure that sterilization (temperature, steam, duration) is completed.
Packaging of items for sterilization
· Packaging of items: either
- without package if items are to be used immediately
- fenestrated drums or boxes
- heavy duty paper: wrapping paper, kraft paper or news paper (2 layers)
- closely-woven linen (2 layers)
- mixed (1 layer of paper, 1 layer of linen)
Paper plus linen is advisable if item is to be stored several weeks (because more resistant than paper alone and best barrier for germs than linen alone).
Fenestrated containers should be equiped with a filter (a layer of heavy duty paper see above) accross the windows within the container or around the load to be sterilized so as to filter air during the drying phase after auto-craving. The paper should be checked and renewed regularly.
· If the autoclave is not equiped with a drying system, drying up of items inside boxes and drums is often unsastifactory. It is easier when the items are packed with paper or linen.
· Packed items should be placed vertically in the autoclave basket (not lying flat).
· Small packages and small drums are preferable to large ones.
· Needles and syringes: separate plunger and barrel of syringes and stick needles onto a gauze swab.
· Swabs and drapes should not be compressed inside boxes or drums.