Enzymatic Cleaning Solution for a Clean Bill of Health: Is it safe?
By Brian Kern
Every healthcare facility struggles to define exactly when an instrument is safe for surgical use. Prior handling by Central Services (CS) is also scrutinized to ensure the safety of hospital staff. In the world of functional testing, the protection of patients remains the highest priority.
In theory, the liberal application of a range of cleaning solutions eliminates any doubt as to the removal of bioburden. The great irony is that such a strategy may ultimately lead to a disproportionate number of instruments failing their functional tests.
Contrary to popular assumptions, many cleaning solutions leave not only residual bioburden but also lasting instrument damage. It can be a challenge to select a cleaning solution appropriate to today's surgical instrumentation from the seemingly overwhelming number of choices.
For endoscopic instrumentation, a good starting point is eliminating today's broad range of anionic detergents from consideration. In lieu of anionic detergents, the use of a neutral pH enzymatic cleaning solution will be more effective in the removal of bioburden without damaging most instruments. To understand why, a brief understanding of liquid chemistry can be helpful.
Creating the Ideal Cleaning Solution
The composition of soil found on dirty surgical instruments can vary widely. Most commonly found are proteins, fats, carbohydrates, and the various chemical salts that exist in blood and other body fluids. Ideally, a cleaning solution will have a broad spectrum of effectiveness against these various contaminants. Additionally, it should be inexpensive, plentiful, and not harm the device being cleaned.
The logical starting point is to look at a solvent such as water, since it is inexpensive and plentiful. Unfortunately, tap water is only marginally successful in cleaning instruments because of its inability to dissolve certain substances well--particularly oil and fat, which are hydrophobic.
Water has another fundamental problem--surface tension, which keeps it from reaching the tight, confined spaces in surgical instruments where soil can become trapped. For example, surface tension can prevent water from penetrating the trapped soil within the intricate hinge mechanisms of a laparoscopic grasper.
There is a wide need for a solution that can penetrate hard-to-reach areas and dissolve trapped soil. Common organic solvents might meet these criteria, but they too would be a poor choice due to flammability concerns and probable instrument damage.
The ideal solution would combine the benefits of water and organic solvents. It must not only be inexpensive, plentiful, and relatively non-reactive with instruments, but also able to penetrate and lift soil from instruments, suspending them in solution. Thankfully, such a class of molecules exists called surfactants.
The Best of Both Worlds: Surfactants
Surfactants are a broad class of molecules--there are literally millions--with special chemical properties. Some function just like soaps in detergent solution, binding to and lifting soil. The principal difference is that soaps are manufactured from natural products (e.g., animal fats) while surfactants are derived primarily from petroleum. As a result, there are some structural differences between natural and synthetic surfactants, but their function remains relatively the same.
In general, the chemical structure of a surfactant is such that one end of the molecule is hydrophilic (attracts water) and the other end is hydrophobic (repels water). What occurs in solution is that the hydrophilic end orients itself toward water molecules while the hydrophobic end attaches itself to soil. This helps to loosen the soil from the surgical instrument, with the soil eventually being surrounded by surfactant molecules. Since one end of the molecule is attracted to water, the overall effect is to suspend the soil particles in solution. This is important since it prevents the formation of a layer of oil on the surface of the cleaning solution. By suspending the soil in solution, the instrument can be removed from the cleaning sink without re-deposition of soil. To visualize this principle, imagine how hard it would be to clean the plates after dinner if there were a layer of oil on top of the water in the sink basin, instead of droplets suspended in solution by the dish soap.
Some types of surfactants serve as "wetting agents," acting to significantly lower the surface tension of the cleaning solution. This includes many of the surfactant-based solutions found on the market today for instrument cleaning, which are anionic and may have moderate to very high pH values.
By reducing surface tension, wetting surfactants readily penetrate the tight crevices of complex surgical instruments, facilitating a more thoroughly cleaned instrument. At first glance, this may sound like an optimal solution for cleaning complex surgical instruments. However, a lower surface tension often brings with it unintended, and sometimes undesirable, consequences.
What Goes in May Not Come out
Corroded beyond recognition, this endoscope was left soaking in a phenolic-based cleaning solution for a week. Use of a neutral pH enzymatic dramatically reduces the risk of corrosion, providing a balanced pH solution.
Consider the distal tip of an endoscope, and the glass assembly referred to as the "distal window." Around this lens is a joint composed of either an epoxy-type resin compound or a metal solder joint, depending on whether the endoscope is non-autoclavable or autoclavable, respectively (when available, autoclavable endoscopes should be chosen since they offer not only autoclavable convenience but tend to be more robust when exposed to damaging chemicals).
Damage or trauma to a telescope can cause stress fractures to develop along this joint. Since stress fractures are often invisible to the naked eye, it is quite common to find endoscopes with this type of damage in clinical use. Unfortunately, stress fractures can serve as pathways for fluid invasion into the endoscope. And this is where the cleaning solution's surface tension becomes so crucial.
Fluid invasion may be prevented if the stress fracture is small and the cleaning solution has a high enough surface tension. But surfactant-based detergents sometimes have a very low surface tension, meaning that fluid invasion is actually quite likely to occur.
Moreover, the same surfactant that readily penetrates the endoscope's small, fractured joints will remain there during subsequent rinse treatments. This occurs because the surface tension of the surfactant-based cleaning solution is low enough to penetrate into the joint while the surface tension of the rinsing agent (water) is too high to penetrate the joint. Surfactant molecules remain in the joint when the penetrated fluid dries. Repetitive cleaning cycles eventually create a surfactant plug that may seal a small fracture and remain there for long periods of time. Application of solutions capable of dissolving such plugs, such as the buffered peracetic acids found in some sterilization systems, are sometimes blamed for damaging an endoscope when, in fact, the damage has been present for a very long time but masked by the plug formation.
Problems associated with surfactant-based cleaning solutions are not limited to endoscopes. When these cleaning solutions are allowed to dry on the high frequency connectors found on electrocautery instruments, they can interfere with current conduction--creating a potentially dangerous spark-gap. Such interference can be direct when the surfactant residuals do not allow proper contact or indirect through the oxidation of such contacts. For these reasons, surfactant-based solutions should be avoided when cleaning electrosurgical instrumentation.
Neutral pH Enzymatics
Anionic surfactant detergents have their place, but there is another choice in cleaning solutions for today's complex instrumentation. Generically referred to as neutral pH enzymatics, these solutions also contain surfactants--but the selected surfactants are different in several key respects.
A high pH solution is alkaline and will attack instrument materials, particularly metals. In fact, many anionic detergents are so high in pH they must contain rust inhibitors. Since enzymatic solutions are neutral in pH, they are not likely to promote instrument corrosion.
Enzymatic cleaning solutions use surfactants specifically selected to have a negligible impact on surface tension while still suspending soil particles. Since fluid penetration into tight joint fractures is kept to a minimum, residual surfactant simply washes away from the instrument during the rinse cycle following enzymatic cleaning.
Perhaps the most important feature of an enzymatic cleaning solution is its enzyme formulation. Whereas anionic cleaning solutions depend primarily on mechanical action for the removal of bioburden, enzymatics use active enzymes to break up the complex proteins, carbohydrates, and fats that coat an instrument following exposure to tissue and fluids. By directly attacking, breaking down, and digesting the bioburden, enzymatic cleaning solutions can be far more effective than passive anionic surfactant solutions.
Enzymatic solutions may contain one or more different types of enzymes to help in the removal of bioburden. Indeed, the choice of enzymes can determine the difference between an average and a highly effective cleaning solution.
In selecting an enzymatic solution, bear in mind that seldom is only one type of enzyme sufficient. For instance, the inclusion of an enzyme which attacks only proteins may be of little value if the protein structure is encapsulated in carbohydrate structures, which must be eliminated first. For this reason, multiple enzyme solutions are almost always preferred. Examples of multiple enzyme formulations are the Endozime® products from Ruhof Corporation (Mineola, NY), a company that pioneered the development of surgical enzymatic cleaning solutions.
Clean and Cleaner
In many instances, the simple process of cleaning an instrument with an enzymatic solution is sufficient to render the device safe for handling. However, some devices may require further processing by subjecting the device to a disinfecting solution or process. This may include sterilization or high-level disinfection. Remember, the types of solutions or processes used must be appropriate for the device. Mistakes in this area can become costly.
Brian Kern is the Technical Services manager at Karl Storz Endoscopy - America, Inc. (Culver City, Calif).
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