Steam Sterilization

Microorganisms need certain conditions in order to live and reproduce. These conditions may include a specific temperature, moisture level, pH and even osmotic pressure. Sterilization used in electrolysis is usually heat based. The most effective and widely used form of heat sterilization is steam under pressure. The ability of air to carry heat is directly related to the amount of moisture present in the air. The more moisture present in the air, the more heat can be carried. Steam is one of the most effective carriers of heat. For instance, when you are cooking beef, like an eye of the round. It can be tough when roasted in a covered pan in the oven, but just add a little water in the bottom of the pan, and you will find that the meat will be tender. The temperature is the same and the time of roasting is the same, but the result is different. Now add another parameter, add pressure. By putting this same roast in a pressure cooker you can reduce the time it takes to cook this roast by at least three quarters, and you still get just as tender a finished product. Now let us look at the instruments used in your practice. When clean instruments are subjected to steam under pressure, the protective outer coat, or layer or microorganisms is first softened, which allows heat to quickly coagulate the sensitive protein material within, thus effectively killing the organisms. There are four conditions that must always be met in order for steam to successfully sterilize. The steam must contact all surfaces of the instrument, because steam is a surface sterilant. The steam must make contact with any microorganisms in order for the sterilization to take place. The second condition is temperature. The steam within the sterilization chamber must be at least 121 degrees centigrade (250 degrees Fahrenheit) throughout the exposure time so that sterilization can take place. Steam will transmit its thermal energy to the item so that both the steam and the item reach the same temperature. The third parameter is exposure time. There is correlation between the time and temperature called time/temperature ratio. The higher the temperature of the steam the shorter the time required to achieve sterilization. The exposure time at 121 degrees centigrade for sterilization to take place is 12 minutes. This does not include the conditioning (heating up), or exhaust time. Total cycles take from 30 to 45 minutes. The final condition is moisture. For successful sterilization steam must be saturated, which means that it reaches a humidity of 100%. When all these parameters, contact, temperature, exposure time and moisture are met, successful sterilization takes place. An autoclave is another word for a steam sterilizer. All autoclaves work on the principle that when a chamber is closed the steam replaces the air which is exhausted out. There are several types of table top autoclaves available. There is a model with a chamber of one or two cubic feet for sterilizing small sets of instruments as well as small bowls and other small equipment. Distilled water is placed in the bottom of the chamber and is heated to create steam. As the pressure within the chamber increases until the desired temperature is reached, sterilization can then take place. There is also a model that uses a cassette that acts as both the steam chamber and the package. Distilled water is placed in a container which feeds into the machine, which is then heated to create steam, which is then fed into the cassette. As the steam fills the cassette, the pressure increases and the heat increases until the desired temperature is met. Just like the others, distilled water is used which is placed in the bottom of the chamber. A basket is inserted where instruments needing sterilization are placed. The water is heated just like the others to produce steam, which as the temperature increases, increases the heat until the exposure temperature is reached. In this column, in the last several issues of the COPE newsletter, the reprocessing of instruments has been discussed. Subjects covered were, why is sterilization important, the procedure for cleaning instruments, and all of the methods of sterilization and disinfection. When an item needs to be sterilized either between clients or at the time of use, they can be sterilized by steam under pressure (by the autoclave), dry heat or chemicals (by vapour or liquid). In most cases dry heat or chemical sterilization are used only if the item is moisture or heat sensitive. Of all of the methods of sterilization available, the method of choice is still steam under pressure. Autoclaving is still the one that is most reliable, easy, and in the long run, the most inexpensive.