Although a proportion of anaesthetic and surgical equipment is disposable nowadays, there is still a significant amount of cleaning and sterilisation required, and with the emergence of new organisms, the methods used have come under closer scrutiny. It is worth noting, in passing, that hand cleanliness of staff coming into contact with patients has also come under close scrutiny in recent years. Cleaning of equipment involves the physical removal of as much of the infectious agent as possible, usually using water and a detergent, and is an important precursor to disinfection or sterilisation. It can be done manually where automated devices are unavailable. Ultrasonic washers are sometimes used, as are irrigation pumps for flushing out the lumina of tubes. There is a difference in definition between disinfection and sterilisation. Disinfection is merely the killing of non-spore producing micro-organisms. It kills most bacteria except mycobacteria and spores, and it kills some fungi and some viruses. A higher level of disinfection ensures the destruction of mycobacteria, and most fungi and viruses. Sterilisation is required to kill all micro-organisms, including spores, fungi and viruses. Prions are, however, resistant to most sterilisation procedures. To disinfect or sterilise the modes of heat, chemicals or radiation are used. Moist heat is much more efficacious at coagulating bacterial protein than dry heat, which requires higher temperatures for longer periods to guarantee effect. Moist heat achieves this by increasing the permeability of the organism’s cellular structure to the heat. A hot water washer or low temperature steam applied to instruments for fifteen minutes kills bacteria, but not spores. Higher temperatures are achievable by pressurising the steriliser (Boyle’s law). The modern autoclave uses steam at 134°C and 2 bar, when 3½ minutes is sufficient to kill all organisms, providing the steam can reach the instruments; however, to dry the equipment, the steam is removed and replaced with sterile air, the total cycle time being 10 minutes. Rubber and plastic materials degenerate after some time with this regime, and a combination of 121°C for fifteen minutes, or 115°C for thirty minutes can be used instead.
Effect of Dry Heat and Hot Water Processings on Cellulose III Crystallite of Cotton and Lyocell Fibers Treated with Liquid Ammonia.