Sterilization

Do you know what your steam quality is?

By Thomas "Chip" Moore

Every CS manager needs to understand generation systems

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The quality of the steam inside central service department sterilizers plays an important role in equipment performance. Yet many CS managers and surgery departments have little understanding or appreciation for steam generation and distribution systems. It’s important to develop a good working relationship between the steam producer and the steam user to optimize day-to-day operations. Doing so will help in troubleshooting everything from the cause of wet loads to those unusual noises that come from the steam distribution system.

Every day, U.S. health care facilities use steam sterilizers to prepare medical devices for patient use. The process includes decontamination, cleaning, inspection, packaging, sterilization, storage for the terminal process or flash sterilization for immediate use.

For each of these steps, there are recommended practices and guidelines for doing it right. The sterilizer is a Class II medical device. It is manufactured per design controls with a quality management system in place to satisfy the medical device regulatory requirements. What do these two subjects—cleaning/sterilization by the health care facility and sterilizer performance—have in common? In a word, it is repeatability, day in and out. Yet, the quality of steam supplied and connected to the sterilizer may vary from day to day or even hour to hour.

In a typical U.S. health care facility, steam is generated in a large central boiler, often with multiple boilers installed for backup capacity (see illustration in Table 1). The steam generated is used for heating and cooling the facility, for the laundry, for the dietary department and for sterilization. It is generally recognized that less than 5 percent of the steam generated daily is used for the sterilization process.

boiler

Viewed on a nationwide basis, however, this 5 percent translates to at least 500,000 sterilization cycles daily. Unfortunately, many managers who operate the boilers do not have an appreciation for sterilization requirements. On the other hand, central supply managers and surgery departments often have little understanding or appreciation for steam generation and distribution systems. A good working relationship between the steam producer and the steam user is essential for optimum day-to-day operations. The relationship becomes even more critical during renovation projects and routine maintenance.

Steam begins with tap water, which can vary from a high to low mineral content (impurities). Water is the only common substance that can exist in solid, liquid and vapor forms (i.e., ice, water and steam). It is a good solvent and the purer it gets, the more aggressive it becomes.

Maintaining the water quality inside the boiler is a complex science. Chemicals are added to keep a certain pH inside the boiler. If the impurities are not removed or neutralized, a wide range of problems will occur (e.g., scaling, corrosion, carryover or oxygen pitting). The list of chemicals that may be required ranges from sodium hydroxide to increase alkalinity, chelants that form heat-stable soluble complexes of calcium and magnesium to control scaling, to amines that control steam-line corrosion by forming a protective film on metal surfaces. The FDA provides guidance on the amount of amines used in steam but it is specific to food service, not sterilization. Along the steam distribution system, steam cools and condenses. That is why it’s important to have condensate return lines to capture the treated water and reduce the need to treat additional system makeup water.

Steam ins and outs

Steam is a vapor with a highly transferable heat content, which is ideal for sterilization. Steam quality is expressed in terms of saturation. Some moisture is essential to the sterilization process. The acknowledged value for high-quality steam is 97 percent dry vapor by weight with no more than 3 percent moisture content (see Table 2). As steam leaves a boiler, it is probably 97 percent saturated. As it travels the distribution system, however, there are many places and reasons why steam cools and condenses. Working traps and drip legs located at key points along the distribution system provide the means to keep the steam vapor close to saturation and to return treated condensate to the boiler.

table

If you hear noises from the steam distribution system, chances are you have wet steam. The noise is called “water hammer.” Steam traps come in many different sizes and shapes and their selection should be based on a specific application.

All the traps and other mechanical devices in the steam distribution system should have a regularly scheduled maintenance program with supporting documentation. Nothing is worse for a sterilizer than a high percentage of water in the initial surge of steam into the chamber.

Any discussion of steam quality should include factors that inhibit the sterilization process. Water supplied to the boilers contains oxygen, carbon dioxide, plus some other inert gases that don’t cause much of a problem. Treatment of the supply water includes a process known as de-aeration that heats the incoming treated water with live steam.

The presence of oxygen and carbon dioxide in the steam can cause pitting and corrosion within the distribution system. From a sterilization viewpoint, the presence of these two elements (referred to as noncondensable gases) in the steam supply can prevent steam contact to all surfaces, a requirement for the sterilization process. The acceptable percentage of non-condensable gases is very low (3 percent). Superheat conditions, essentially dry heat, also will cause sterilization failure. Should superheat conditions occur inside a sterilizer, fabric may scorch or deteriorate.

Superheat can be caused by excessive temperature in the sterilizer jacket versus the chamber or by pressure reduction in the steam supply. Superheat conditions occur rarely in sterilization while poor quality steam (less than 97 percent saturation) can occur anytime. The effects of noncondensable gases on the sterilization process are relatively new considerations in health care facilities and should be given greater attention.

Sterile at last

Producing a sterile product for patient use requires three elements to be in sequence. The load needs to be prepared and loaded in the sterilizer so that steam can contact all surfaces. The sterilizer needs to be functioning as designed. The steam supply should be within the specified pressure range and at least 97 percent saturated.

Should one of these elements not be proper or to specification, sterilization failure can occur. The comparison is to a three-legged stool, where all three legs need to be of equal length.

Although there is no supporting evidence, past experience shows that 60 percent of all related sterilization issues can be traced to the steam supply, 30 percent to the sterilizer performance and 10 percent to the wrapping and loading techniques. Here are some examples:

A hospital in the Pacific Northwest had ongoing wet-pack problems. The root cause was that 31 traps in the steam distribution system were not operating.
A Southern California hospital had years of unexplained wet packs. During a renovation, they found a major “dip” in the steam lines that didn’t have traps, drip legs or condensate return lines.
A major hospital in Canada had both positive biological indicators and positive Bowie-Dick Test results. The root cause was a ruptured disk in an air-operated valve in the steam line, allowing air to leak into the steam supply lines.
A major hospital in the Midwest capped the drip legs on three pieces of central supply equipment, which caused the condensate to back up to the sterilizers.

These are just a few of the many sterilization issues that occur daily. Wet loads disrupt the normal flow of sterile products for patient use, causing anxiety throughout the institution and testing the facility’s ability to resolve the problem quickly. Finger pointing doesn’t help. Root cause analysis helps when it is followed by implementation of corrective action.

Today, health care facilities are working their sterilizers harder than ever due to surgical workload increases. Wet packs, like speed bumps, slow down the central supply operation. One option to keep sterilizer productivity going when the steam connected is of questionable quality, is to install small, appropriately sized standalone boilers near the sterilizers and bypass house steam altogether. Treating the water to these standalone boilers is required, as is performing routine boiler blowdown to remove deposit buildup.

In the January/February 2008 issue of IAHCSMM’s Communiqué, there is a self-study article on “Implementing a Quality Service Management System.” In the article, quality is defined as “the consistent delivery of products and services according to established standards.”

The sterilizer, a Class II medical device, is manufactured to a performance standard under a quality management system umbrella. It is designed to perform with at least 97 percent saturated steam connected and delivered at certain dynamic pressure ranges. The missing factor in health care facilities are measurable goals for the steam quality connected to their sterilizers.

Measuring steam quality requires technical expertise and equipment. At minimum, each health care facility should create a baseline steam quality report, if for no other reason than to have a reference point when future steam-related issues occur. A good way to start is to capture steam condensate near the sterilizer and analyze it for contaminates.

Testing steam quality

There are several methods to test steam quality. One uses an electronic device inside the sterilizer to capture temperature measures at multiple points. This is called chamber mapping. The other method is from the European Norm (EN) 285, the performance standard for large sterilizers. It involves taking three steam samples near the sterilizer to measure non-condensable gases, superheat and steam saturation percentage. This method requires a special fixture with three ports that connect to the sampling instrumentation.

What can be done until the health care facility has a good understanding of the steam quality connected to their sterilizers? The following are some helpful troubleshooting tips:

Beads, puddles and lakes: Visible signs of moisture sitting on nonwoven wrap material after a steam cycle is an indication of steam quality problems.
Rough steam quality measurement: Weigh a textile pack. Place it on the empty sterilizer load car and run a vacuum cycle at normal exposure time and temperature, with little or no dry time programmed. Weigh the textile pack again. The percentage of weight gain is close to the moisture content of the steam. The weight gain should be around 2 percent or less.
A fun test: Line the sterilizer load car with nonwoven wrap material, using tape to keep the material in place. Run two normal vacuum cycles, one without dry time, the second with dry time. After the cycle without dry time, observe the amount and location of the visible moisture sitting on the nonwoven material. There should be a small amount of moisture (beads) under heavy metal structures. Now run the normal vacuum settings with dry time. The nonwoven material should be dry before starting the cycle and the load car should have cooled down to room temperature. There should be no visible signs of moisture after the normal vacuum cycle.

Each sterile product produced for patient use by a health care facility should be of the same quality every day. The cleaning process is very important. The load preparation is important. Loading the sterilizer load car is important. The sterilizer should be operating at the original manufacturer’s utility requirements and performance specification. Finally, each health care facility should know the quality of the steam connected to round out a complete quality management system. Every health care facility should have a sterilization process that is repeatable. Why not start today?

Thomas “Chip” Moore retired from Getinge after a 39-year career in sales and marketing sterilizers and sterilization systems, new product introduction and training and organizing educational seminars. He is a member of AAMI, IAHCSMM and AORN Special Assemblies.

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