Most, if not all, of the washers utilized in today’s hospitals rely on high-impingement washing action to complete bioburden reduction levels that allow safe handling of instruments prior to sterilization. However, high impingement was not exclusively developed for the decontamination of surgical instrumentation in hospitals. From home dishwashers to car washes, high impingement is employed in many ways by means of water, chemicals, solid material and air.
Complete a Google search of “high impingement” and you will find more than 3 million pages. Buried somewhere in the information highway is little mention as to the significance this process plays in today’s decontamination of surgical instruments. Instrument washers, both single chamber, tunnel, and cart washers, rely on the water impingement as part of the disinfection and cleaning process. Furthermore, impingement classifications that apply to surgical instruments can be defined as followed: The mechanical process of a cleaning solution striking a surface. Impingement usually occurs in a spray process, and helps dislodge soils from surfaces. A process resulting in a continuing succession of impacts between (liquid or solid) particles and a solid surface.
Impingement is best described in a hospital decontamination setting as the mechanical action of pressurized water forced through spray jets to remove debris. High impingement is achieved by means of forced water through water channels which are then directed to spray arm jets by utilizing high-pressure water pumps. The relative efficiency of a washer/disinfector’s mechanical impingement action is between 50 percent to 60 percent of forced water delivered by the spray arm’s jets.
Consequently, a failure in any one spray arm will affect the washer’s overall ability to clean instruments. Spray arms typically spin in a clockwise direction on all levels, with directional jets on opposing arms. Most rack-mounted spray arms have jets on both top and bottom, while the machine mounted arms spray in one direction — up or down.
Additionally, the remaining cleaning process is about 40 percent dependent on chemical, thermal and human factors related to processes that cannot self adjust or respond to a failure of the spray arm(s):
• Cold and hot water hardness
• Water temperature
• Enzyme dilution
• Low alkaline detergent dilution
• Lubrication dilution
• Rinse cycle
• Reverse osmosis water purity
• Metal mass
• Placement of instruments
• Layering
• Poor routine maintenance
• Improper rack selection
• Overloading
• Bioburden level and location
• Target surface
Spray arms mounted both in the washer and on the selected washer racks complete a circuit. A decrease or loss of pressure in any one spray arm will reduce the overall impingement process. One way of understanding this is to picture a standard sprinkler system for watering your yard; lose a sprinkler head and watch what happens. Leaks in most, if not all, water systems result in reduced pressure; high-impingement washers rely on just that — sustained pressure.
Moreover, the closer the instrument is to the spray arm or impingement action in an upright position, the better the final results. Making things even more difficult for automated washers and central service professionals is that there are no defined load limits or configurations, let alone studies that measure and support the process pre- to post-washer.
Instruments’ Positioning Has Effect on Impingement
Impingement efficiency as previously mentioned is dependent on contact to the primary surface area which is directly related to the placement and positioning of instruments. Surgical instrumentation’s primary area is the surface that has the highest contact with human tissue, including hinged and unibody areas. High Impingement is more successful when direct contact can be made on the targeted surface. Positioning of instruments becomes even more challenging when the quantity or mass of instruments exceeds the washer’s ability and there are no limits set.
Piling of instruments is one area that affects the impingement process as well as poor rack selection and layering. Using perforated bottom flash pans with solid stainless steel sides also reduces or redirects impingement as will the use of hold-down screens. Rack-mounted spray arms which have jets aimed both up and down cannot complete direct upward contact to the vital instrument surfaces when perforated bottom trays are used. Mesh-bottom trays, however, allow for better flow but pose other problems when instruments become lodged in the wire sides and bottoms. The tradeoff has yet to be measured.
Layering occurs when utilizing a single-level, general-purpose rack with instruments placed in a flash pan and adding a hold-down screen; this reduces or redirects the water spray resulting in splash rather then a cutting action. Poor positioning affects all cycles, including the final rinse, which is the last and most important cycles in an automated washer. Final rinse cycles remove residual chemicals and debris that piling and poor placement inhibits.
Stringing Instruments and Impingement
One attempt to solve poor positioning is the five-inch stringer; when used properly instruments are in an up-right position which greatly improves the washer impingement process. However, layering becomes a challenge when instruments are strung with no space between each one, resulting in reduced surface contact with all cycles in the washer. Overloading the stringer makes things even more challenging, in that there are no limits to the number of instruments other then the length of it. When compressed to fit that last instrument, water flow becomes a problem, thus inhibiting the overall washing process.
Along with size configurations of each type of instrument and what constitutes a proper opening, stringing has some limitations. A ring-handled instrument’s optimal opening is about a 90-degree angle, which allows flowthrough the box-lock area. A nine-inch instrument's box-lock surface area cannot be opened to the same distance/angle as a five-inch instrument on the same size stringer. Laying the stringer on the side completely eliminates the target area of the instrument, namely the box-lock and tissue contact area serrations or teeth.
Where this was a great first step at addressing the positioning problem, it added additional processing time. If you pre-string, then you must have a well-defined manual process, starting in the operating room, with soaking and removal of gross visible bioburden. The angle of the stringed instruments must be standing upright, following the stringer manufacturer’s recommendations to allow impingement contact and flow for optimal results.
Washer Rack Selections’ Effect on Impingement
Washer racks come with a number of levels, resulting in varying distance from the spray arm. The farther the distance, the less effective the impingement becomes. Keep in mind that as water falls from level to level, it interferes with the spray arm’s water impingement due to redirection caused by increased volume resulting in a splash affect. Simply put, water volume increases as it drops from each level. Overloading the second, third, fourth or fifth level can have decreased impingement due to increased masses of instruments and poor placement on each level. For best performance, place smaller sets on lower levels. Moreover, the more levels, the more spray arms, which results in additional maintenance and a higher potential for failure and decreased impingement.
When making the choice for instrument washer racks, the three-level rack provides optimal performance while maintaining volume and throughput. Four- and five-level racks add time to loading and can slow production due to increased wait time both pre- and post-washer. Sending a four- or five-level rack through the washer half empty defeats the purpose of increased volume, which is the only reason for purchasing one.
The two-level rack in most washers is designed for instruments on the top and basins or pans on the bottom. Distance of the spray arm from to the target surface on the bottom is more suited for larger items. Impingement is reduced as a result of the distance, producing a splash effect more so than a cutting action achieved on the first level. The closer the better applies in most, if not all cases.