Sterilisation of instruments

Stage 1 - preparation of the materials - is aimed at thorough mechanical cleansing of instruments; removal of pyogenic compounds and destruction of hepatitis viruses. The person responsible for this should always wear gloves.

The instruments that were used but not infected will be washed under running water separately with a brush for 5 minutes. In contrast, blood-stained equipment must be washed immediately (without subsequent drying! ), then soaked in one of special washing solutions, warmed to a temperature of 50 °C for 15-20 minutes, syringes being dismantled before washing.

The formulations of the washing solutions are as follows:

• Solution A

Perhydrol - 20 g washing detergent - 5 water - 975 ml.

• Solution B 2, 5% hydrogen peroxide - 200 ml washing detergent - 5 water - 795 ml.

After soaking the instruments, particularly their corners and folds, instruments are washed with brush in the same solution and then rinsed in warm water for 5 minutes and in distilled for another. The instruments are then packed into a drying air steriliser under the temperature of 85 °C; thereupon these are ready for sterilisation.

The instruments contaminated with pus or intestinal contents are first soaked in enamel containers with 5% lysol for 30 minutes, then washed in the same solution with brush, rinsed with running water and soaked in one of the washing solutions; the further steps are as given above.

It is noteworthy that the equipment used to operate on patient with anaerobic infection should be soaked in a special solution that contains hydrogen peroxide (6%) and washing agent (0, 5%) for 1 hour, then washed with a brush in the same solution before boiling for 90 minutes (it is only after this that the instruments will be ready for thorough sterilisation as is the case with instruments which have not been infected).

Injection needles are washed by first attaching syringes to them using warm water and 1% sodium hydrocarbonate, the canal being emptied with a mandrin and washed with 0, 5% liquid ammonia and running water. The needle with its mandrin still in is then boiled for 30 minutes in 2% sodium bicarbonate and after 8-12 hours boiling is repeated in distilled water for 40 more minutes and dried. After this, the canal of the needle is to be dried by pushing in ether or alcohol with a syringe. The needles which have been contaminated with pus are thoroughly washed, the canal washed with running water and then soaked for an hour in 5% lysol, simultaneously washing the canal with lysol with the aid of a syringe before proceeding as in the case if the instruments have not been contaminated.

Drug and blood transfusion sets need to be washed thoroughly to prevent post-transfusion reactions and complications. Recently, these have been made disposable (to be used only once), which are sterilised by the producer. The other sets that can be resterilised will be dismantled immediately after use - the glass side, droppers and plastic tubes - to be thoroughly washed with running water by pressing on the plastic side to clear away any blood remnants. Certain parts of the system are soaked for 2 hours in a special solution (1% sodium bicarbonate and 1% ammonium solution) which had previously been warmed to the temperature of 60 °C. The other parts of the set should be boiled for 30 minutes in distilled water after washing with running water, washed again with water under pressure on the plastic tube to force out any blood stains, and boiled once again for 20 more minutes in distilled water. Thereafter, this set is arranged and packed for sterilisation.

Currently, medical gloves are disposable and previously sterilised by the manufacturer. If plastic gloves are to be used several times, those stained with blood are not disposed but washed under running water until all the blood is washed away, dried with a towel and soaked for 30 minutes in 0, 5% ammonium or in a washing solution A or B. They are then to be washed with running water, dried, and packed for sterilisation.

To make sure the materials are free of blood stains following presterilisation, the benzidine test is applied. Three drops of 1% benzidine and hydrogen peroxide are put on the material or instrument tested; a bluish-green coloration suggests the presence of blood. This requires that washing (stage 1) be repeated.

Stage 2 - arrangement and package for sterilisation. For sterilisation in an air-drying steriliser the instruments are arranged in a metallic box, vertically and in one layer with the lid open but lying by its side. Dismantled syringes are wrapped in two layers of special thick paper.

For the sterilisation in an autoclave (steam under pressure) the instruments are wrapped into towels or cotton cloth made into bag and arranged on a metal tray or net. Sets of instruments for typical operations on the heart, lung, bone, vessels are sterilised together; they are arranged on special trays and wrapped in sheets.

The cylinder and piston of the syringe are wrapped separately into gauze napkins then into a cotton bag, which is then placed into the dressing box. The sets are wrapped in cotton napkins and put in the steriliser.

Dried rubber gloves are sprinkled with talcum powder both inside and outside, arranged in pairs in gauze napkins and placed in a separate dressing box.

Stage 3 - sterilisation. Sterilisation of instruments, syringes (with the inscription «200 °C»), needles, glass containers is done with an dry-air oven (fig. 1). The materials are freely arranged on the steriliser's shelf and the apparatus switched on. With its doors open the steriliser is heated to a temperature of 80-85 °C to dry its interior and the instruments for 30 minutes. The doors are then closed and the temperature increased to 180 °C and maintained automatically; within 60 minutes the materials are sterilised. After switching off and cooling to 70-50 °C the door is opened, the metal container with the instruments is covered with its sterile lid. Within the next 15-20 minutes when the steriliser is cool the materials can then be removed.

Fig. 1. Dry heat steriliser.

a - anterior view; b - lateral view; 1 - body; 2 - control panel; 3 - support; 4 - thermometers (direct contact and transistor thermal regulators); 5 - electric heaters; 6 -door.

Whilst working with the dry-air oven steriliser safety measures must be taken: the apparatus must be earthed, after sterilisation the door can be opened only when the temperature has reduced to 70-50 °C. It is forbidden to use a faulty apparatus.

Sterilisation of instruments can be done in an autoclave (fig. 2). The wrapped up materials are packed into the sterilising chamber. If the items are packed into a dressing box, then its lattice should be opened. Dressing boxes and other containers must be placed freely to allow an equal distribution of the steam.

Surgical instruments are sterilised within 20 minutes at 2 atmospheres (1 atmosphere = 1, 013 x10⁵ pa) which is the equivalent of 132, 9 °C. The starting time for sterilisation is counted from the start of the required pressure. Plastic drainage tubes are sterilised at 1, 1 atmospheres (steam temperature of 120 °C) for 45 minutes. When the dressing box is removed from the autoclave after sterilisation, its opening is closed immediately.

Sterilisation in the dry-air oven and autoclave are considered as the main methods. Boiling as a method of sterilisation is used in small centres, where there are no centralised sterilisation systems. Stationary or portable electrical heaters are used to sterilise instruments, glass objects, plastic drainage tubes, catheters and gloves. Distilled water is used to raise the point of boiling; 20 g of sodium hydrocarbonate per 1liter of water is added to destroy the bacterial sheath (2% solution). The bottom of the water heater is lined with a thin layer of material made up of cotton wool and gauze to absorb sediments onto it and not onto the instruments.

Dismantled, instruments are put on special nettrays and lowered by hooks down into the boiler such that their handles are left outside the boiler, which is then closed. Sterilisation time is 40 minutes from the onset of boiling. At the end of sterilisation the net tray with instruments is raised by the hooks, allowed to drain and brought to a special table, which had been previously covered with a sterile sheet folded into four layers. The operating theatre nurse arranges the instruments on a big sterile table.

Instruments contaminated with pus and intestinal contents, after special cleaning as stated above can be sterilised by boiling for 90 minutes using a different boiler.

Instruments used for a patient with gas gangrene have to be handled carefully, with thorough cleaning and subsequent fractional sterilisation by boiling. They are boiled for an hour, removed from the boiler and left to stand at room temperature for 12-24 hours (to allow the spores to geminate), and then boiled again for another one hour.

The main method used to sterilise plastic items (gloves, catheters, drainage tubes) is autoclaving. In very rare cases they are boiled for 15 minutes

Sterilisation of instruments that cannot stand heat (endoscopes, thoracoscopes, laparoscopes, the set of instruments used for artificial blood circulation or for heart-lung bypass), are done in special gas sterilises (fig. 3). Materials for sterilisation are put in airtight sterilisation chambers filled with ethylene dioxide. Exposition time is 16 hours with the temperature of 18 °C. A mixture of ethylene dioxide and methylene bromide under the temperature of 55 °C can also be used to sterilise within 6 hours.

Fig. 2. Steam steriliser (autoclave).

a - lateral view; b - anterior view; 1 - thermometer; 2 - manometer; 3 - heater; 4 - inlet tap; 5 - outlet; 6 - external wall; 7 - internal wall.

Sterilisation of optical instruments (laparo-scopes, thoracoscopes, and choledochoscopes) can be done in alcohol solutions of chlorhexidine and pervomur. Sterilisation of apparatus and instruments, using chemical compounds should be done in metallic containers with covers to prevent evaporation and pollution of the air in the room. In the absence of special containers they are sterilised in containers made of enamel or glass. The instruments are covered with water such that all of them are under the water and covered with the lid.

In emergency, when it is not possible to sterilise the instruments using any of the above-stated methods, sterilisation can be achieved by burning. 15-20 ml of alcohol are poured into a metallic pan or dish, several instruments are put inside and the alcohol is burned. The burning method is not very reliable, can cause fire and explosion (in the presence of vapours of ether, etc). Because of these the method of burning is used only in extreme conditions, strictly taking fire safety measures.

When cutting instruments (scalpels, scissors) are sterilised in the ordinary way, they turn blunt, so it is better they are sterilised without heat. After pre-sterilisation they are put into 96% of ethyl alcohol for 30 minutes or in triple solution for 3 hours. Cutting instruments are allowed to boil for only a short period of time. The blades of scalpel are wrapped in gauze and placed on separate net tray and boiled for 10 minutes without adding sodium bicarbonate, and then they are put in 96% ethyl alcohol for 30 minutes.

Fig. 3. Gas steriliser.

Stage 4 - Keeping the sterilised materials. Sterile materials are kept in special containers. Sterile and non-sterile items may not be kept at the same container. Materials can stay sterile in a dressing box, which has not yet been opened for 48 hours. If before packing in the dressing box the materials were wrapped in (towels, sheets or napkins) as is the case with rubber drains), then they can stay sterile for 3 days. In cases of centralised sterilisation syringes can be sterile for 25 days.

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