Chapter 14: High-Temperature Sterilization PDF

# Chapter 14: High-Temperature Sterilization ## Learning Objectives As a result of successfully completing this chapter, the reader will be able to: - Discuss factors that impact the effectiveness of sterilization - Discuss the advantages of steam sterilization - Provide basic information about th...

# Chapter 14: High-Temperature Sterilization ## Learning Objectives As a result of successfully completing this chapter, the reader will be able to: - Discuss factors that impact the effectiveness of sterilization - Discuss the advantages of steam sterilization - Provide basic information about the types of steam sterilizers available - Discuss basic information about steam sterilizer cycles - Describe the conditions necessary for an effective steam sterilization process - Explain basic work practices for steam sterilization - Review sterilization process indicators and explain the need for quality control ## Introduction High-temperature sterilization is the process of choice in many healthcare facilities. It is achieved by subjecting items being processed to thermal energy from moist heat (steam). - High-temperature sterilization has long been recognized as an effective way to kill microorganisms. - Because of its successful record of efficacy, reliability and low cost, steam is the most frequently used sterilant for devices not adversely affected by moisture or heat. - Other methods are only used when the object being processed cannot withstand the heat and/or moisture required for steam sterilization. As with all sterilization methods, devices to be processed must first be: - Thoroughly cleaned - Decontaminated - Properly prepared - Cleaning involves the removal of all visible soil. - Decontamination kills most but not all microorganisms. - Sterilization is required to kill any remaining microorganisms, including spores. Sterilization failure could result in serious, even life-threatening, patient outcomes. A **Sterile Processing (SP)** technician must learn the components of a steam sterilizer to better understand how it operates and supports quality outcomes and patient safety. ## Factors that Impact Sterilization The success of every sterilization process is not guaranteed. Several factors and conditions impact the effectiveness of all sterilization methods, including those using high temperature. These factors include: - **The type of microorganisms present** - Some microorganisms are more resistant to the sterilization process than others. - **The design of the medical device** - Complex devices present a challenge to the sterilization process. - **The number of microorganisms (bioburden) present** - When there are more microorganisms on a medical device, the sterilization process becomes more difficult. - **The amount and type of soil present** - Soil acts as a shield to protect microorganisms. **Note:** The cleaning process is absolutely essential as a first step in sterilization. A device can be cleaned without sterilizing, but sterilization cannot be achieved if a device hasn't been thoroughly cleaned. - **Bioburden:** The number of microorganisms on an object; also called "bioload" or "microbial load." ## Advantages of Steam Sterilization Steam is the sterilant of choice for several reasons: - Low cost - Rapid sterilization cycles - Relatively simple technology - Leaves no chemical residues or byproducts Steam sterilizers date back to the early days of formalized healthcare. Prior to steam sterilization, boiling water was commonly used to kill bacteria. Scientists recognized the need to increase temperatures beyond the boiling point to kill greater numbers of heat-resistant bacteria. An early pressure steam sterilizer (autoclave) was developed in 1880 by Charles Chamberlain, a colleague of Louis Pasteur. The autoclave resembled a pressure cooker and was able to use pressurized steam to reach temperatures of 248°F (120°C) and higher. Although it looks primitive by today's standards, it was the first-generation model of the steam sterilizers used today. ## Anatomy of a Steam Sterilizer Steam sterilizers come in many sizes and cycle choices, from small tabletop sterilizers used primarily in clinic and dental settings, to mid-sized and large units designed to sterilize large quantities of items. ## Components of Steam Sterilizers An SP technician must know the components of a sterilizer to better understand how it operates. ### Jacket Sterile Processing departments (SPDs) typically use jacketed sterilizers. - In most hospitals, steam is supplied to the sterilizers from a main steam line. - Other sterilizers in clinics, dental practices and some SPDs manufacture their own steam or attain their steam from an independent generator. ### Chamber The interior chamber walls of the sterilizer are heated by steam in the metal jacket; this helps minimize the amount of condensation (moisture) that forms when hot steam contacts the chamber walls as a cycle begins. The jacket surrounds the sides, top and bottom of the vessel, and steam circulates in this space to preheat the interior chamber walls. ### Door, Gasket and Chamber Drain - The **door** is the weakest part of a steam sterilizer. It has a safety locking mechanism that automatically activates when chamber pressure is applied, and it can only be unlocked when pressure is exhausted. - The **door gasket** is designed to maintain a tight seal that prevents steam from escaping from the chamber, and air from entering the chamber. - On most steam sterilizers, the **chamber drain** is located at the front or center of the floor. The drain screen must be cleaned at least daily and more often, as needed. Debris in the chamber drain screen can impede cycle performance by blocking the removal of air and steam. ### Thermostatic Trap The **thermostatic trap** is located in the drain line. The drain and the area surrounding it are the coolest areas in the sterilizer. A sensor in the chamber drain measures steam temperature and automatically controls the flow of air and condensate from the sterilizer chamber. ## Physical Monitors - Physical monitors verify that the parameters of the sterilization cycle have been met. - Physical monitors on a sterilizer record the time, temperature and pressure. - SP technicians must check them throughout the sterilization cycle to ensure that necessary parameters are met. A printout from a steam sterilization cycle usually contains the following information: - Date and time the cycle began - Selected cycle parameters such as type of cycle, sterilization temperature and dry times - A written record of actual cycle activities (e.g., temperatures, exposure times and pressure). ## Types of Steam Sterilizers Used in Sterile Processing Several types of steam sterilizers are available today. Healthcare facilities purchase sterilizers that will meet their specific needs, including chamber size, style and available cycle options. ### Tabletop Sterilizers - Tabletop sterilizers are frequently used in clinics and dental offices. - These units operate by having water poured into the sterilizer, either manually or automatically, through a port or the bottom of the chamber, and are electrically heated until the water turns to steam. - Water quality is an important factor and is specified in the sterilizer instructions for use (IFU). - In a tabletop sterilizer cycle, steam rises to the chamber's top and as more steam is produced, cooler air is forced out through the drain near the bottom of the chamber. - When steam enters the drain, a thermostatic valve closes and causes the steam to build up pressure until the operating temperature is reached. - When the proper temperature is reached, the timer is activated. - At the end of the cycle, the relief valve opens to allow the steam to escape. - The steam passes through the water reservoir where it condenses back to water. - After the pressure has dropped to zero, the door can be opened. ### Gravity Air Displacement Sterilizers - Some small- to medium-sized sterilizers have gravity displacement and dynamic air removal cycles. - In a gravity displacement cycle, steam enters the chamber and because air is heavier than steam, the steam forces the cooler air to the bottom of the chamber and out the drain. - Gravity air displacement sterilizers have physical monitoring controls such as temperature-indicating charts and printouts for recordkeeping. ### Dynamic Air Removal Sterilizers - Dynamic air removal sterilizers are similar in construction to gravity air displacement sterilizers, except there is a vacuum pump or water ejector that removes air from the chamber more effectively during the preconditioning phase, prior to reaching the exposure temperature. - Dynamic air removal sterilizers usually operate at higher temperatures [270°F to 275°F (132°C to 135°C)] than gravity sterilizers. - The preconditioning phase increases the speed of operation and reduces the chance of air pockets in the chamber during the cycle. - Dynamic air removal sterilizers use different types of preconditioning methods for air removal, including variations of prevacuum air removal and above-atmospheric-pressure processes, such as the steam flush pressure pulse (SFPP) process. - The preconditioning cycle removes air from both the sterilizing chamber and the load before the chamber is pressurized with steam to the exposure temperature. Effective air removal is critical for steam penetration. ### Prevacuum Steam Sterilizers - In prevacuum steam sterilizers, the dynamic air removal cycle depends on one or more pressure and vacuum sequences at the beginning of the cycle to remove air during the preconditioning phase. - Typical operating temperatures are 270°F to 275°F (132°C to 135°C). - To ensure air removal in these sterilizers, the integrity of the sterilizers should be checked daily by processing a Bowie-Dick (or daily air removal) test. - Some sterilizers have an automatic cycle (vacuum leak test) to test the vacuum tightness of the chamber. ### Steam Flush Pressure Pulse Sterilizers - SFPP sterilizers use a repeated sequence of a steam flush and pressure pulse to remove air from the sterilizing chamber and processed materials. - Air removal occurs above atmospheric pressure; no vacuum is required. - This process rapidly removes air from the sterilizer's chamber and wrapped items. ## Steam Sterilizer Cycles Along with understanding the types of steam sterilizers used in the healthcare facility, SP technicians must also understand how these machines function. To begin, SP technicians should be familiar with two basic sterilization cycles: - Immediate use steam sterilization (IUSS) - Terminal sterilization - Items processed using IUSS must undergo the same cleaning and preparation as items that are terminally sterilized. - Sterilizers used for IUSS are typically located outside of the SPD. - Their intended use is for the emergency sterilization of instruments when there is not enough time for terminal sterilization. - These types of sterilization processes have little or no dry time; therefore, at the end of the sterilization process, instrumentation is expected to be hot and wet. - Time is usually shortened due to the reduced dry cycle. - Not all items have IUSS instructions from the device manufacturer; consult the medical device manufacturer's IFU to determine if IUSS is possible for the device(s) to be processed and to learn the proper sterilization cycle. - Items sterilized using IUSS should be used immediately and cannot be stored for use at a later time, unless such a process has been approved by the U.S. Food and Drug Administration (FDA). - By contrast, "terminal sterilization" refers to the sterilization of an item that is expected to be dry upon completion of the sterilization process. - Terminal sterilization is most often performed in the SPD. A saturated steam sterilization cycle has at least three (and possibly four) phases: - Conditioning - Exposure - Exhaust - Drying (in most instances) ### Conditioning At the beginning of the sterilization cycle, steam enters at the upper back portion of the sterilizer. As steam enters, air is displaced through the drain. As steam continues to enter the sterilizer's chamber, pressure begins to rise, as does the steam temperature. ### Exposure After the desired temperature is reached, the sterilizer's control system begins timing the cycle's exposure phase. Note: The instrument manufacturer's IFU should be consulted for the specific time and temperature for each instrument/set sterilized to ensure the cycle is appropriate. ### Exhaust At the end of the exposure phase, the chamber's drain is opened, and the steam is removed through the discharge line. This creates a void in the chamber; filtered air is gradually reintroduced into the chamber and the chamber gradually returns to room pressure. ### Drying Drying begins at the conclusion of the exhaust phase. Dry times are based on the device, packaging and sterilizer IFU. At the end of this dry time, the end-of-cycle signal sounds and the door may be opened. ## Conditions Necessary for Effective Steam Sterilization Regardless of the type of steam sterilization method used, the same four conditions - contact, temperature, time and moisture - must be met. ### Contact The most common reason for sterilization failure is the lack of contact between steam and the entire surface of the device being sterilized. This failure may be related to human error or mechanical malfunction. Frequent causes of steam contact failure include: - Failure to adequately clean the object being sterilized - Any coating of soil, such as protein or oils, can protect the microorganisms from direct steam contact. - Density - Sets that are too dense, or instruments positioned in a way that does not allow steam contact. - Packages wrapped too tightly - If packs are wrapped too tightly, air becomes trapped and cannot escape. - Loads that are too crowded - Packs must be arranged with adequate spacing on the cart. If they are packed too tightly, air may be entrapped, and steam may not be able to penetrate all areas. - Containers that are positioned incorrectly - Basins and other items that can hold water must be positioned so air can be removed and water (condensed steam) can escape. - Clogged drain strainer - Most sterilizers have a small drain strainer at the bottom of the chamber to keep lint, tape and other small objects from entering the exhaust line. - Mechanical malfunctions - Defective steam traps, clogged exhaust lines and similar mechanical malfunctions can occur and cannot be repaired by an SP technician. A qualified service representative should be called to perform the necessary maintenance. - Utility malfunctions - Boiler or steam delivery system problems can occur, and a qualified service representative is needed to make repairs, as specified in the sterilizer manufacturer's service manual. **Note:** While mechanical malfunctions can occur, many sterilization failures are caused by human error and can be prevented by good work practices. ### Temperature To be effective, steam sterilization must occur at specific temperatures. These temperatures are needed to kill heat-resistant bacteria. The two most commonly encountered temperatures for steam sterilization are gravity sterilization 250°F (121°C) and dynamic air removal 270°F to 275°F (132.2°C to 134°C). ### Time The steam sterilization process can only be effective if all items within the load are exposed to the elevated temperatures and steam contact (moisture) for an adequate amount of time. Inadequate sterilization exposure times can lead to failure of the sterilization process. ### Steam Quality and Moisture A specific type of steam quality is required to perform steam sterilization. Steam quality is the steam characteristic reflecting the dryness fraction (weight of dry steam present in a mixture of dry saturated steam and entrained water) and the level of noncondensable gas (air or other gas that will not condense under the conditions of temperature and pressure used during the sterilization process). Dry, saturated steam is required for effective steam sterilization. Saturated steam acts like fog because it holds many tiny water droplets in suspension. The moisture content of saturated steam should possess a relative humidity (RH) of 97% to 100%. In other words, steam ideally should consist of (by weight) two to three parts of saturated water and 97 to 98 parts of dry, saturated steam. - **Saturated steam** is similar to air with 100% RH. When saturated steam cools, water condenses as a liquid. The pressure exerted by saturated steam is constant for a given temperature, and the pressure varies in direct proportion to that temperature. In other words, the higher the temperature, the higher the pressure. To increase steam temperature, pressure must be increased; to decrease the steam temperature, pressure must be decreased. - **Saturated steam:** Steam that contains the maximum amount of water vapor. - **Noncondensable gases:** Gases that cannot be liquified by compression under the conditions of temperature and pressure used during the sterilization process. ## Basic Work Practices to Facilitate the Steam Sterilization Process Medical devices must be properly prepared before sterilization to ensure steam will come in contact with all surfaces. This section provides sterilization preparation guidance for processing some common medical devices. ### Preparing Devices and Packs for Steam Sterilization Effective sterilization requires that the sterilizing agent contact all surfaces of the devices for the prescribed time. Air removal, steam penetration and condensate drainage are enhanced by proper positioning and by the use of perforated or mesh-bottom trays or baskets. Instrument sets should be prepared in trays large enough to equally distribute the mass, and the configuration of instrument sets should be evaluated to help ensure they remain dry. - When possible, sterilizing textiles and hard goods in separate loads. If this is not possible, textiles should be placed on top shelves with hard goods placed below to avoid condensation runoff from the hard goods onto the textiles. ### Loading a Steam Sterilizer To ensure full steam contact and removal of air, the sterilizer must be properly loaded to allow adequate air circulation and drainage of the condensate. Care should be taken not to exceed the load requirements for the sterilizer. Prior to loading, refer to the specific sterilizer's IFU for loading requirements. - Allow for proper steam penetration and avoiding overloading. Packages must be placed for efficient air removal, steam penetration and evacuation.. - Positioning instrument sets in a way that allows air to exit and steam to enter. - Ensuring there is a visible space between packs to allow steam circulation and drying. - When combining loads, placing hard goods, such as rigid containers, on the bottom to prevent condensation from dripping onto lower packs. - Ensuring that packages do not touch chamber walls. - Standing basin sets on edge. They should be tilted for drainage so if water is present, it will run out. - Positioning textile packs so the layers within them are perpendicular to the shelf. - Standing paper/plastic peel pouches on edge using a basket or rack. - Ensuring that surgical instrument trays with perforated bottoms and most rigid container systems sit flat on the shelf to maintain even instrument distribution and facilitate proper drainage. - If a shelf liner is used, it should only be comprised of absorbent material. ### Unloading a Steam Sterilizer When sterilization is complete, follow the sterilizer IFU for opening the sterilizer door. When the cart is removed, it should be placed in a low-traffic area where there are no air conditioning or other cold air vents in close proximity. For sterilizers without carts, items should remain in the sterilizer chamber until properly cooled. - An infrared device or other type of temperature-sensing device may be used to verify that sterilized items have reached room temperature. - The cooling time may be only 30 minutes for small sets or peel pouches but can take two hours or longer for larger sets. - The cooling time must account for critical factors such as the type of sterilizer used, the design of the device and packaging being sterilized, and the temperature and humidity of the room. - If packages are touched at this point, the vapor present might carry microorganisms from one's hand through the packaging material, leading to contamination of the item. - The load contents should be visibly free of any liquid. Water droplets on the outside of packages or on the rails of carts signal that every item in the load should be visually inspected. - **Caution:** Do not touch items during visual inspection. Wet items should be considered contaminated, even if they have not been touched. - **Do not unload packages before they are cool.** Placing hot or warm packages on cold surfaces will cause condensation to develop beneath and/or between them. If warm packages are placed in plastic protective covers, condensate will be trapped until opened, and the moisture may damage items underneath the protective cover. - Handle the sterile packages as little as possible. Items should not be moved or touched until they have cooled to room temperature. ### Controlling Wet Packs - Wet packs may occur when a steam sterilization process is used. - Packages are considered wet when moisture in the form of dampness, droplets or puddles of water are found on or within a package after a completed sterilization cycle. - Moisture can create a pathway for microorganisms to travel from the outside to the inside of a package. - If moisture is present on one pack, the problem may be isolated to that one set. - If there are several wet packs from one load, the entire load should be considered wet. - Wet packs cannot be released and should be reported for immediate follow up. - **A wet pack is considered contaminated and must be completely reprocessed.** ### Wet Pack Documentation - All wet packs should be documented. - Documenting wet pack occurrences may identify a pattern that can pinpoint the root cause. - Identifying the root cause of the wet packs is crucial for preventing additional wet packs. - External moisture on packs is usually noticed immediately when the packs are removed from the sterilizer. - Internal moisture will not be noticed until the packs are opened for use unless the moisture wicks through the wrap. ### Causes of Wet Packs Primary causes of wet packs arising from SP preparation techniques include: - Packs that were improperly prepared or loaded incorrectly for sterilization. This is the most frequent cause of wet packs. - Heavy or dense instrument sets - Packs wrapped too tightly - Improperly prepared items such as items wrapped while moist - Metal steam positioned in a way that allows water to pool or trap steam - Instrument and basin sets that are too dense or overloaded - Linen packs wrapped too tightly, causing them to retain moisture - Improper placement of concave items, such as medicine cups, in a position that does not allow for drainage - Not using correct filters or incorrectly placing the filter on a container Another reason for wet packs may be the sterilizer itself. Listed below are two of the most common reasons that can be identified by an SP technician: - Gasket not completely intact. - Clogged chamber drain strainer. - Other causes of wet packs can only be identified and resolved by a qualified sterilizer service technician. Such causes may include: - Broken valves - Malfunctioning steam traps or drain check valves - Faulty sterilizer gauges or controllers - Clogged drain line - Faulty drain valves - Wet packs may also be caused for reasons occurring outside the SPD. - Some factors from outside the SPD that can contribute to wet packs, including: - Steam quality that does not meet the requirements of the sterilizer - Blocked steam lines - Boiler feed water that contains too many non-condensable gases, including air - Boiler not properly maintained - Malfunctioning steam traps or check valves - Poorly engineered steam piping - Increased demands for the steam supply - Wet packs can also be caused by environmental factors such as removing a hot load and placing it in an air-conditioned area or an area with humidity exceeding 70%. ## Extended Sterilization Cycles Healthcare facilities typically use standard cycles for a majority of items processed. Occasionally, however, medical instrumentation manufacturers' IFU may include an extended exposure time, which is known as an extended cycle (based on the device's complex design and materials). - SP technicians must obtain, review and consistently follow the manufacturer's written recommendations for all medical devices they process. - Most medical devices require standard cycle times. Damage to some items can occur if items requiring standard sterilizing times are processed with other devices that require an extended cycle. - Items should not be sterilized with items that require a different cycle time. - Items should never be sterilized in any cycle that deviates from the specific manufacturer's instructions. ## Cleaning and Maintaining Sterilizers The sterilizer manufacturer's written recommendations for sterilizer maintenance must always be followed. The following general cleaning and maintenance guidelines illustrate manufacturer recommendations: - The chamber drain strainer should be removed at least daily and cleaned thoroughly under running water using a non-abrasive brush and mild detergent. This procedure may be needed more frequently depending on the types of loads processed. - The door gasket should be inspected and wiped clean daily with a clean, damp, non-linting cloth. During inspection, look for defects or signs of wear or deterioration, especially if the unit has a vacuum cycle. - Carriages, carts and loading baskets should be routinely cleaned with a mild solution. - Follow the manufacturer's IFU for cleaning and lubrication requirements. - Carriages, carts and loading baskets should be checked to ensure they are not damaged and can move freely in and out of the sterilizer chamber. - Follow the manufacturer's instructions about the need and method for cleaning and flushing the chamber's drain. Air and steam will not pass efficiently if the drain line is blocked. - Cool the chamber before performing any cleaning or maintenance procedure. - The inside of the chamber should be cleaned according to the manufacturer's instructions. - Clean with non-abrasive and non-linting products. - Rinse detergent and residue from the chamber thoroughly to avoid deposits on devices during sterilization. - Strong abrasives or steel wool should never be used on the sterilizer because they can scratch the surface and encourage corrosion. - Inspect recording devices daily, including paper charts and printer paper. ## Conclusion SP technicians who understand the steam sterilization process reduce the risk of sterilization failure. Knowing when there could be an issue with a steam cycle may allow the load contents to be reviewed and, if necessary, reprocessed before the items are distributed or used on a patient. ## Resources - ANSI/AAMI ST79:2017 & 2020 Amendments A1, A2,A3, A4 (Consolidated Text) Comprehensive guide to steam sterilization and sterility assurance in health care facilities. - Centers for Disease Control and Prevention. Guideline for Disinfection and Sterilization in Healthcare Facilities. 2008. - Huys J. Sterilization of Medical Supplies by Steam, Volume 1, General Theory. 2010. ## Sterile Processing Terms - **Bioburden** - **Saturated steam** - **Noncondensable gases**