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By Brian Kern
Every healthcare facility struggles to define exactly when an instrument issafe for surgical use. Prior handling by Central Services (CS) is alsoscrutinized to ensure the safety of hospital staff. In the world of functionaltesting, the protection of patients remains the highest priority.
In theory, the liberal application of a range of cleaning solutionseliminates any doubt as to the removal of bioburden. The great irony is thatsuch a strategy may ultimately lead to a disproportionate number of instrumentsfailing their functional tests.
Contrary to popular assumptions, many cleaning solutions leave not onlyresidual bioburden but also lasting instrument damage. It can be a challenge toselect a cleaning solution appropriate to today's surgical instrumentation fromthe seemingly overwhelming number of choices.
For endoscopic instrumentation, a good starting point is eliminating today'sbroad range of anionic detergents from consideration. In lieu of anionicdetergents, the use of a neutral pH enzymatic cleaning solution will be moreeffective in the removal of bioburden without damaging most instruments. Tounderstand 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 chemicalsalts that exist in blood and other body fluids. Ideally, a cleaning solutionwill have a broad spectrum of effectiveness against these various contaminants.Additionally, it should be inexpensive, plentiful, and not harm the device beingcleaned.
The logical starting point is to look at a solvent such as water, since it isinexpensive and plentiful. Unfortunately, tap water is only marginallysuccessful in cleaning instruments because of its inability to dissolve certainsubstances well--particularly oil and fat, which are hydrophobic.
Water has another fundamental problem--surface tension, which keeps it fromreaching the tight, confined spaces in surgical instruments where soil canbecome trapped. For example, surface tension can prevent water from penetratingthe trapped soil within the intricate hinge mechanisms of a laparoscopicgrasper.
There is a wide need for a solution that can penetrate hard-to-reach areasand dissolve trapped soil. Common organic solvents might meet these criteria,but they too would be a poor choice due to flammability concerns and probableinstrument damage.
The ideal solution would combine the benefits of water and organic solvents.It must not only be inexpensive, plentiful, and relatively non-reactive withinstruments, but also able to penetrate and lift soil from instruments,suspending them in solution. Thankfully, such a class of molecules exists calledsurfactants.
The Best of Both Worlds: Surfactants
Surfactants are a broad class of molecules--there are literallymillions--with special chemical properties. Some function just like soaps indetergent solution, binding to and lifting soil. The principal difference isthat soaps are manufactured from natural products (e.g., animal fats)while surfactants are derived primarily from petroleum. As a result, there aresome structural differences between natural and synthetic surfactants, but theirfunction remains relatively the same.
In general, the chemical structure of a surfactant is such that one end ofthe molecule is hydrophilic (attracts water) and the other end is hydrophobic(repels water). What occurs in solution is that the hydrophilic end orientsitself toward water molecules while the hydrophobic end attaches itself to soil.This helps to loosen the soil from the surgical instrument, with the soileventually being surrounded by surfactant molecules. Since one end of themolecule is attracted to water, the overall effect is to suspend the soilparticles in solution. This is important since it prevents the formation of alayer of oil on the surface of the cleaning solution. By suspending the soil insolution, the instrument can be removed from the cleaning sink withoutre-deposition of soil. To visualize this principle, imagine how hard it would beto clean the plates after dinner if there were a layer of oil on top of thewater in the sink basin, instead of droplets suspended in solution by the dishsoap.
Some types of surfactants serve as "wetting agents," acting tosignificantly lower the surface tension of the cleaning solution. This includesmany of the surfactant-based solutions found on the market today for instrumentcleaning, which are anionic and may have moderate to very high pH values.
By reducing surface tension, wetting surfactants readily penetrate the tightcrevices of complex surgical instruments, facilitating a more thoroughly cleanedinstrument. At first glance, this may sound like an optimal solution forcleaning complex surgical instruments. However, a lower surface tension oftenbrings with it unintended, and sometimes undesirable, consequences.
What Goes in May Not Come out
Consider the distal tip of an endoscope, and the glass assembly referred toas the "distal window." Around this lens is a joint composed of eitheran epoxy-type resin compound or a metal solder joint, depending on whether theendoscope is non-autoclavable or autoclavable, respectively (when available,autoclavable endoscopes should be chosen since they offer not only autoclavableconvenience but tend to be more robust when exposed to damaging chemicals).
Damage or trauma to a telescope can cause stress fractures to develop alongthis joint. Since stress fractures are often invisible to the naked eye, it isquite common to find endoscopes with this type of damage in clinical use.Unfortunately, stress fractures can serve as pathways for fluid invasion intothe endoscope. And this is where the cleaning solution's surface tension becomesso crucial.
Fluid invasion may be prevented if the stress fracture is small and thecleaning solution has a high enough surface tension. But surfactant-baseddetergents sometimes have a very low surface tension, meaning that fluidinvasion 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. Thisoccurs because the surface tension of the surfactant-based cleaning solution islow enough to penetrate into the joint while the surface tension of the rinsingagent (water) is too high to penetrate the joint. Surfactant molecules remain inthe joint when the penetrated fluid dries. Repetitive cleaning cycles eventuallycreate a surfactant plug that may seal a small fracture and remain there forlong periods of time. Application of solutions capable of dissolving such plugs,such as the buffered peracetic acids found in some sterilization systems, aresometimes blamed for damaging an endoscope when, in fact, the damage has beenpresent for a very long time but masked by the plug formation.
Problems associated with surfactant-based cleaning solutions are not limitedto endoscopes. When these cleaning solutions are allowed to dry on the highfrequency connectors found on electrocautery instruments, they can interferewith current conduction--creating a potentially dangerous spark-gap. Suchinterference can be direct when the surfactant residuals do not allow propercontact or indirect through the oxidation of such contacts. For these reasons,surfactant-based solutions should be avoided when cleaning electrosurgicalinstrumentation.
Neutral pH Enzymatics
Anionic surfactant detergents have their place, but there is another choicein cleaning solutions for today's complex instrumentation. Generically referredto as neutral pH enzymatics, these solutions also contain surfactants--but theselected 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 theymust contain rust inhibitors. Since enzymatic solutions are neutral in pH, theyare not likely to promote instrument corrosion.
Enzymatic cleaning solutions use surfactants specifically selected to have anegligible 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 rinsecycle following enzymatic cleaning.
Perhaps the most important feature of an enzymatic cleaning solution is itsenzyme formulation. Whereas anionic cleaning solutions depend primarily onmechanical action for the removal of bioburden, enzymatics use active enzymes tobreak up the complex proteins, carbohydrates, and fats that coat an instrumentfollowing exposure to tissue and fluids. By directly attacking, breaking down,and digesting the bioburden, enzymatic cleaning solutions can be far moreeffective than passive anionic surfactant solutions.
Enzymatic solutions may contain one or more different types of enzymes tohelp in the removal of bioburden. Indeed, the choice of enzymes can determinethe difference between an average and a highly effective cleaning solution.
In selecting an enzymatic solution, bear in mind that seldom is only one typeof enzyme sufficient. For instance, the inclusion of an enzyme which attacksonly proteins may be of little value if the protein structure is encapsulated incarbohydrate structures, which must be eliminated first. For this reason,multiple enzyme solutions are almost always preferred. Examples of multipleenzyme formulations are the EndozimeÂ® products from RuhofCorporation (Mineola, NY), a company that pioneered the development of surgicalenzymatic cleaning solutions.
Clean and Cleaner
In many instances, the simple process of cleaning an instrument with anenzymatic solution is sufficient to render the device safe for handling.However, some devices may require further processing by subjecting the device toa disinfecting solution or process. This may include sterilization or high-leveldisinfection. Remember, the types of solutions or processes used must beappropriate 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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