Medical sterilizers are machines that kill all germs on surgical instruments between operations, including the hardy bacterial spores, using steam, gas or plasma. They record every cycle, so that the hospital can prove that each tray of instruments was sterile. In Indian hospitals, this work is done in the central sterile services department (CSSD).
Instruments follow a fixed route. After an operation, they are washed in a machine called a washer-disinfector. Staff check the instruments, pack them into trays and wrap each tray. They load the trays into a sterilizer. After sterilization, the trays are stored until the next operation that needs them.
There are three main methods. A steam sterilizer, or autoclave, uses steam under pressure. A common cycle holds 134°C for at least 3 to 4 minutes. With the air removal at the start and the drying at the end, the whole cycle takes about an hour. Instruments that heat would damage, such as cameras and some plastic tools, are sterilized at a low temperature with hydrogen peroxide gas or plasma. Ethylene oxide gas also works at a low temperature, but the materials then need many hours for the gas to leave them.
Proof comes in three layers. First, the sterilizer's software records the time, temperature and pressure through every cycle. It fails the cycle if any value goes outside its limits. Second, chemical indicators, strips of special ink inside each pack, change colour when the right conditions are reached. Third, biological indicators, small vials of hardy bacterial spores, are run in some loads and then kept warm to see whether anything grows. If any spores survive, the load was not sterile.
Consider the CSSD of a 300-bed hospital in Surat. A technician scans the barcodes of 12 trays into a load, and starts a 134°C cycle. The sterilizer records 4 minutes at 134°C, at about 2 bar above normal air pressure, and passes the cycle. Surgical instrument tracking software links the cycle record to all 12 trays. The next morning, one tray from this load goes to theatre 3. If a biological indicator from that load had failed, the software would list all 12 trays, so that every one of them could be called back.
Hospital accreditation in India expects records of this kind. The trays include large sets, such as those used to fit an orthopaedic implant, which can hold well over a hundred pieces. The same kind of machine is built at a larger size for drug factories, as bioprocess and sterilisation equipment. There, loading is sometimes done by an industrial robot.