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By Lawrence F Muscarella, PhD
Developing and marketing a liquid chemical sterilant (LCS) for reprocessingendoscopes is a more formidable task than often appreciated. The ideal LCS,among other factors, is safe to healthcare staff and the environment, relativelyinexpensive, rapidly sporicidal, compatible with delicate instruments,non-foaming, and remains active in the presence of protein and organic soil. Nocurrently marketed LCS satisfies all of these criteria. With most drugs, foreach of its benefits a LCS will typically have a salient shortcoming. Forinstance, LCSs that are rapidly sporicidal typically tend to be more corrosive,resulting in higher endoscope repair and maintenance costs.1,2Despite their limitations, LCSs are convenient, relatively fast-acting, anduniversally used to reprocess flexible endoscopes and other instruments.
Among other advantages including convenience, LCSs are routinely used toreprocess gastrointestinal (GI) endoscopes in or near the patient's procedureroom. 3 For healthcare facilities lacking a large inventory ofendoscopes, the use LCSs avoids having to transport these expensive instrumentsto a remote central processing department (CPD), which can be costly and canremove the endoscope from service for a prohibitively long period of time.However, the convenience and cost-savings afforded by LCSs are not without adown side. Tension can develop between patient safety and the healthcarefacility's desire to reprocess endoscopes as quickly as possible. Two effectivesterilization processes routinely used in CPDs are ethylene oxide (EtO) gas andsteam autoclaves. The use of either for endoscope reprocessing is prohibitive;the former typically requires a 24-hour aeration time before the endoscope canbe returned to service for reuse, and the latter destroys the heat-sensitive anddelicate materials used in the construction of fiberoptic flexible endoscopes.
LCSs can to some degree mollify this tension, providing healthcare staff withan effective 'point-of-use' reprocessing method that yields high-leveldisinfected endoscopes in less than 20 minutes. (Heating some LCSs, or alteringtheir concentrations or pH, can enhance their biocidal properties and furtherreduce their immersion times.) To be sure, manufacturers relentlessly seek todevelop and market LCSs labeled to 'sterilize' endoscopes (and otherinstruments) in less than an hour. Whether the US Food and Drug Administration(FDA) will only for the second time in almost 15 years approve a LCS labeled forthe 'sterilization' of endoscopes during an immersion time of less than an houris unclear, although, in my opinion, not likely.
As with many biocidal agents, issues can arise with LCSs (e.g.,glutaraldehyde, ortho-phthalaldehyde, hydrogen peroxide, and peracetic acid)that warrant consideration and caution. For instance, the labels of mostFDA-cleared LCSs, which some infection control and healthcare staff may findconfusing,3 provide two instrument immersion times: one for high-leveldisinfection, and another, typically requiring a considerably longerimmersion time (e.g., 3 to 10 hours), for sterilization.
Despite their dual label claims, it is my opinion that the FDA's originalintent was to limit the use of LCSs intended for reprocessing flexibleendoscopes only to high-level disinfection4,5 having not fullyanticipated that a LCS might be marketed exclusively for sterilizing endoscopes.Whereas sterilization is a multi-step process that includes, among other steps,cleaning, instrument wrapping, and specific quality controls such as the routineuse of biological indicators (BIs), immersing an item in a LCS is virtually asingle-step process.4,6 Confusing a multi-step and complete sterilizationprocess with a LCS's single-step and limited sporicidal process can, inmy opinion, result in a false level of assurance and increase the risk ofpatient infection.7
In summary, LCSs are convenient and easy to use but have several salientshortcomings that limit their effectiveness and reliability and call intoquestion their current FDA-cleared labels that claim instrument sterilization.First, items reprocessed using a LCS lack a shelf-life, as they cannot bewrapped and therefore are susceptible to re-contamination during handling andstorage. Second, in addition to conveying a higher sterility assurance level(SAL) than heat, EtO, and plasma sterilization proceses, 5,6 LCS-basedprocesses lack essential quality controls and cannot be reliably monitored usingBIs: the bacterial endospores on the BI's strip may be rinsed-off during itshandling and immersion in the LCS, rendering the BI's results meaningless.8
Third, unlike pressurized steam that can diffuse through instruments'materials and patient debris and kill otherwise inaccessible microorganisms,LCSs require direct contact with the microorganisms to be effective.6LCSs are also viscous, which can limit their flow through narrow lumens andorifices.5,6,9 Further, the effectiveness of LCSs depends on thethoroughness of the cleaning process, which, if performed manually, is difficultto standardize, control, and monitor. An unclean instrument cannot bedisinfected or sterilized. No doubt, the complex physical designs of most modelsof flexible endoscopes neither facilitate cleaning of every internal surface norpermit direct microbiological sampling, as required to validate the process'seffectiveness.
The physical properties of LCSs and the designs of some complex instrumentsboth contribute to limiting the effectiveness and anticipated reliability of LCS-basedprocesses, compared to heat-based processes,4 as well as toincreasing the probability that a flexible endoscope's internal surfaces mayremain contaminated following immersion in the LCS. The need to re-designflexible endoscopes that provide direct access to every internal surface and canwithstand the rigors of thermal sterilization cannot be overemphasized.
Fourth, unlike with heat and EtO gas (or plasma) sterilization, LCS-basedprocesses uniquely require a final water rinse to remove potentially toxicresidues. Indeed, the quality of the healthcare facility's water is oftendifficult to control and monitor. And if the final water rinse containsmicroorganisms, the instrument may become re-contaminated after chemicalimmersion.4,6,7 As a result, this essential final water rinse is, inmy opinion, the Achilles' heel of current LCS-based processes. Multiple cases ofpatient infection and deaths linked to contaminated rinse water have beenrecently reported. 0-11 When properly maintained and replaced,bacterial filters can improve the water's microbiological quality and minimizethe likelihood of instrument re-contamination during the final water rinse. Butbacterial filters are not fail-safe, and their effectiveness after only a fewuses has been reported to fail and permit the passage of bacteria.9,12-14
In conclusion, due to the aforementioned limitations of LCSs and thechallenges posed by complex instrument designs, claims that a LCS reliably'sterilizes' flexible endoscopes are, in my opinion, suspect and warrantcaution. Independent data demonstrating that flexible endoscopes can besterilized using LCSs (or any other method) have not been published.Furthermore, according to the FDA, using LCSs to reprocess surgical instrumentsnot damaged by heat (e.g., rigid endoscopes) is not recommended, due to"the inherent limitation of using (LCSs) for sterilizing medical devices. 5"
As a point of emphasis, sporicidal LCS-based processes are markedly lessreliable than complete sterilization processes. Therefore, limiting the intendeduse of these LCS-based processes to high-level disinfection, especially if usedto reprocess complex instruments, seems indicated and necessary for patientsafety. 4,6
Viewing the outcome of endoscopes immersed in a LCS as being high-leveldisinfected, rather than sterilized, also underscores to staff the importance ofensuring the endoscope has been pre-cleaned immediately after use and has beendried using 70% alcohol followed by forced air before storage, a step whosesafety has been well-documented6,9,10,11 and which may be skipped ifthe intended use of the LCS is to achieve sterilization. 15,16 Also,LCS-based processes that claim to 'sterilize' flexible endoscopes mayparadoxically pose an increased risk of patient infection. 7,15,16
Lawrence F. Muscarella, PhD, is the director, research and developmentchief, and infection control editor in chief, of The Q-Net Monthly, apublication sponspored by Custom Ultrasonics, Inc, based in Ivyland, PA.