Autoclaves: The Most Efficient Method of Sterilizing Instruments and Dressings
Autoclaves are widely recognized as the most efficient method of sterilizing instrument packs and dressings. This method is suitable for most materials and ensures thorough
sterilization to eliminate any potential pathogens. An autoclave essentially functions as a pressure cooker, and in fact, even a domestic pressure cooker can be used to sterilize instruments in the same fashion as smaller autoclaves.
Autoclaves come in various sizes, with the smaller ones designed for doctor’s surgeries offering a choice of temperatures, pressures, and sterilizing times. Even with different capacities, each of these autoclaves maintains their effectiveness in ensuring sterilization.
By increasing the pressure inside the autoclave, the temperature of the water can be raised significantly higher than the boiling point of 100 degrees Celsius at sea level. This rise in temperature is one of the fundamental operating principles for autoclaves in medical settings.
For example, at a pressure of 0.35 kg per cm (5 p.s.i), the temperature can reach 105.5 degrees Celsius, and at 0.7 kg per cm (10 p.s.i), it can reach 115 degrees Celsius. At 1.05 kg per cm (15 p.s.i), the temperature can reach 121 degrees Celsius, and so on—these conditions are routinely achieved by autoclaves in clinical use.
In the sterilizer chamber of an autoclave that has been exhausted of air, the steam effectively fills the free spaces surrounding the load. Importantly, this process highlights how autoclaves can deliver consistent sterilization results.
contact with the cool outer layers of the cloth film, it condenses, leaving a minute quantity of moisture in the fibers of the material. This step demonstrates the inner workings of autoclaves during their sterilization cycles.
The air contained in the spaces between the fibers, being heavier than steam, is displaced downward, and the latent heat given off during the process of condensation is absorbed by the cloth covering, effectively sterilizing it. Such heat transfer is precisely why autoclaves are the gold standard for sterilizing medical textiles.
This process continues as the next film of steam fills the space created when the previous film condenses into water. The steam penetrates the subsequent layers,
condenses, and heats them until the entire load is heated to its inner depth, and no further condensation occurs. The temperature in the core of the pack matches that of the surrounding steam in autoclaves working at optimal capacity.
Autoclaves offer both quick and slow cycles, depending on the materials being sterilized. A quick cycle can heat the water to 134 degrees Celsius for 3.5 minutes under a pressure of 30 lb/in, while a slow cycle,
more suitable for plastics, can heat the water to 12 degrees Celsius under a pressure of 15 lb/in. In practice, instruments are placed in trays or packs,
the autoclave is turned on, and it is left for the desired time. At the end of the cycle, the instruments are ready for use, illustrating the ease of workflow with autoclaves.
One of the main disadvantages of smaller autoclaves is the lack of a vacuum cycle to extract air and dry the packs. However, most materials, including rubber, plastics, and metal,
can be readily sterilized, with the only exception being salted containers. For items like metal and plastics, autoclaves provide reliable results despite this limitation.
To effectively sterilize, steam must displace all the air in the chamber and reach all parts of the load. If the steam contains droplets of water, it can soak into porous materials. Additionally,
if air is not let out, the bottom of the chamber may be much cooler than the top. Therefore, an autoclave must be saturated with steam and held at the desired temperature and pressure for
a critical holding time. The standard holding time is 15 minutes at 121 degrees Celsius, but it may need to be varied depending on the specific requirements. This is one safety guideline that must be followed when operating autoclaves in healthcare environments.
The cycle of operation for a high vacuum/high-pressure sterilizer can be summarized as follows:
1. Pre-vacuum air removal:
The air is removed from the chamber using a vacuum pump and controlled steam pulsations. These actions set the stage for autoclaves to begin sterilizing efficiently.
2. Sterilization:
Steam is admitted to the chamber, and when all parts of the load have reached a temperature of 134 degrees Celsius, it is maintained for 3.5 minutes. Modern autoclaves are designed to monitor and maintain this temperature precisely.
3. Drying:
Adequate post-vacuum ensures drying, which can be checked periodically using a test pack of towels. If the towels, when removed from the sterilizer,
unfolded and allowed to cool, are not damp, the drying process is considered successful—another important feature in many high-end autoclaves.
4. Breaking the vacuum and air replacement:
This step should be completed within 3 minutes through a fiberglass or ceramic-type filter. The chamber is then unloaded, and the packs are marked with
the batch number of that particular load. Prepared trays should have a dust cover applied if they are to be stored for more than a few hours, and the cover should only be applied after the trays have cooled off, just as recommended in manuals for autoclave maintenance.
Single-wall autoclaves, similar to pressure cookers, have several disadvantages.
They do not efficiently remove all the air from the chamber, leaving an unknown quantity of air behind. Additionally, they lack thermometers at the bottom of the chamber,
making it difficult to determine the temperature accurately. Moreover, the load remains moist after sterilization, which can be dangerous as bacteria can enter through the moist wrappings—a critical consideration when choosing among autoclaves for a practice or clinic.
Double-walled autoclaves, on the other hand, can be vertical and rely entirely on gravity to displace the air. In some older autoclaves,
a partial pre-vacuum at the start of the sterilizing cycle caused turbulence when air was admitted, thus hindering the gravity displacement of air. Overall, improvements in autoclave technology have addressed many of these issues over time.
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