The lifesaving diagnoses and procedures performed with endoscopes are a vital part of modern healthcare. However, endoscopes are difficult to clean, particularly because of the persistence of biofilms. This creates challenges for manufacturers, healthcare facilities, sterile processing department (SPD) staff, and regulatory agencies seeking to ensure that these complex devices are processed and stored safely and responsibly.

This analysis reviews current studies of endoscope processing, focusing on persistent problems with human factors challenges created by current cleaning and sampling methods. It also looks at cleaning verification, highlights the academic call to include microbial surveillance as a necessary task, and identifies an emerging technology—turbulent fluid flow (TFF)—that may help to fill the gaps in this area.

Many reports from the Food and Drug Administration's (FDA's) Manufacturer and User Facility Device Experience (MAUDE) database demonstrate that flexible endoscopes can inadvertently cause patient harm due to inadequate removal of soil, such as protein and bacterial bioburden, and improper high-level disinfection (HLD) and sterilization after use. In one surveillance study reported in the MAUDE database, a duodenoscope cultured positive for Staphylococcus aureus bacteria after processing.1  It was reported that the facility failed to properly perform visual checks to determine whether debris was removed and that multiple steps were missed during processing.

Residual soil that is not removed from endoscopes during manual cleaning reduces the effectiveness of HLD and sterilization, placing patients at risk for exposure to other patients' tissue, secretions, and potential pathogens. Studies have described the practical challenges of establishing functional protocols for endoscope processing.2, 3  These studies point out that the previous explanation for processing failures was primarily based on human factors. A closer examination of the designs of endoscopes and the processes of the cleaning identified daunting challenges related to both vision and memory. Because of limited time and resources of SPDs for verification testing of flexible endoscopes, there is a lack of feedback on cleaning efficacy. Implementation of this testing may help identify processing failures before they pose potential risks to patient safety.

One such innovation that can be incorporated into verification testing is TFF. This emerging technology enhances the flushing of endoscope channels for better extraction and can subsequently provide more reliable samples for both cleaning verification and microbial surveillance of flexible endoscopes.

The Human Factors of Processing

From a human factors perspective, endoscope processing is demanding for staff in SPDs. It can be labor intensive, physically taxing, and mentally demanding, requiring manual strength and dexterity, fine motor work, repetitive motion, and memorization of tasks that must be performed in sequence. It can also involve exposure to potentially harmful cleaning solutions and sterilization gases and require the use of personal protective equipment throughout the work shift.

Ofstead et al.3  reported that SPD staff experience pain, fatigue, numbness, and stress due to workload and called for increased automation in processing. Jolly et al.4  found similar challenges in a study introducing volunteers from a nursing school with no prior instrument cleaning experience to endoscope processing. Participants received instructions, written procedures, and diagrams detailing basic endoscope processing, in which five critical subtasks in 76 steps were emphasized (a simplified routine compared with actual processing). None of the participants were able to complete the five critical subtasks.

The results of these studies illustrate the difficulty of learning the many steps involved in endoscope processing, as well as the human factors challenges of performing these tasks quickly, in the proper sequence, and repeatedly throughout the day. In addition, agreements exists among Ofstead et al.,3  Jolly et al.,4  and best practices recommended by the Association of periOperative Registered Nurses (AORN)5  regarding identification of the critical tasks that cannot be missed without compromising cleaning effectiveness. Specifically, AORN recommends the following key tasks in endoscope processing5 :

  • Precleaning. This requires the staff member to disassemble the endoscope and any accessories for wipe down, clean rinse, and damp transport. This step is performed immediately after use in a clinical procedure. After completion of precleaning, the device is transported from the procedure room to the SPD (e.g., by a nurse or clinical technician).

  • Leak testing. This step is performed to determine if the endoscope has any leaks. The technician submerges the endoscope in clean water, then air is forced through the channels. The emergence of air bubbles indicates breaks in one or more channels. If found, these breaks will require repair.

  • Manual cleaning. The technician soaks the scope in cleaning solution (detergent or enzymatic cleaner) and manually brushes the device with (potentially) several different-sized brushes. These tasks require precise movements, counts, repetition, and durations of substeps to process the scope effectively. Channel openings need to be capped in sequence for brushing and rinsing. The knobs, valves, and levers must be opened and closed throughout the process to ensure that the brush has access to the interior areas of the device. Some instructions for use (IFUs) call for visual inspection; however, without a borescope and magnification, the channel interiors cannot be seen adequately, making detection of soil difficult.

  • HLD or sterilization. The technician performs HLD using an automated endoscope reprocessor (AER), with wash cycles selected as specified by the manufacturer. The device manufacturer also indicates whether HLD or sterilization should be used.

  • Rinsing. Postcleaning, the technician rinses the device with alcohol to aid in drying the interior channels.

  • Drying. The technician dries the channels with forced air, with some studies indicating that the air should be continuous for 10 minutes, while exteriors are hand dried. A heated drying cabinet, if available, can improve drying effectiveness, as confirmed by Perumpail et al.6  in a 2019 study of the effect on microbial load when using automated drying cabinets versus standard storage cabinets. The importance of the drying step in preventing biofilm formation cannot be overstated.

  • Storage. Endoscopes are stored in a clean and protected environment.

The human-intensive work of rinsing, brushing, flushing, and drying is meant to combat the organic residue from patient use that can lead to the development of biofilm inside endoscopes. Biofilm is formed when microorganisms adhere to each other and to surfaces where moisture is retained. The microorganisms, which can include bacteria and fungi, secrete a substance that promotes adhesion and protects the organisms from drying, allowing for colony formation.7  This biofilm is what surveillance testing tries to detect, SPD staff seek to prevent, and AER cycles attempt to eradicate. Any moisture that is left behind after drying cycles can host biofilm formation, stressing the importance of correct drying. In 2018, Singh et al.8  demonstrated that most high-concern organisms were reliably eliminated by cleaning verification and channel-purge storage conditions, as indicated in manufacturers' IFUs.

The complexity of endscope processing can be better understood when considering the seven tasks described above in relation to the variety of endoscope models in use at any given healthcare facility and the differences in the IFUs created by the various manufacturers. This complexity exacerbates the problems of training and retention due to the large number of procedures that technicians must learn and remember. Consistent adherence to these specifications creates practical challenges for SPD staff. Hildebrand et al.9  and Ofstead et al.3  conducted extensive site studies and staff interviews and described as many as 200 separate actions required for standardized manual cleaning, followed by HLD in an AER.

The volume of daily patient procedures at many healthcare facilities and outpatient sites dictates that scopes are continually in use or being processed. Even with optimal conditions of time, staffing, supplies, and processes, ensuring optimum endoscope processing is difficult. Following the recommended cleaning processes described above requires a large amount of concentration and physical activity in the manual cleaning phase.

Cleaning Verification and Microbial Surveillance

Recognizing the challenging and complicated processes involved in endoscope processing, professional society guidelines and standards indicate that visual verification alone is insufficient, thereby indicating the need for biochemical testing to verify the effectiveness of the cleaning process:

  • “Efficacy of cleaning has traditionally been evaluated visually; however, visual inspection alone, even with magnification, is not sufficient to determine the cleanliness of complex devices such as flexible endoscopes.”5 

  • “It is a challenge to visualize internal channels. Facilities should determine a method of manual cleaning verification.”10 

  • “This testing should include at a minimum monitoring of the suction/biopsy channel.”11 

AORN5  and SGNA10  recognize that visual inspection for cleaning verification is difficult or impossible, as some channels of an endoscope are simply too narrow to visualize—or the design of the hardware will not allow it. Likewise, ANSI/AAMI ST91:2015 stresses the importance of the suction/biopsy channel, which, by design, comes into direct contact with bodily fluids. Biochemical testing of this channel is indicated for any sort of cleaning verification.11 

Commercially available products and processes can be used to verify the effectiveness of cleaning processes and for microbial surveillance of endoscopes. However, whether using sterile water, buffer solutions, or other media, all methods on the market today require that samples be obtained by passing the medium through the endoscope channels via a painstaking and labor-intensive process. The selected microbial testing medium is pushed (in the case of a swab) or flushed (in the case of a fluid, usually sterile water) through one of the several channels within the endoscope. A sample of the medium is collected from the terminal (distal) end of the channel, then introduced to the chosen method for microbial growth. The most common collection methods are as follows:

  • In the flush-brush-flush method, sterile water is flushed through the channel, which is then brushed and flushed again with sterile water. A channel swab or brush is advanced through the channel.

  • Water is flushed through the channel and a sample is collected, then air is passed through the channel with a syringe (Figure 1).

The extracted samples are tested for residual protein, hemoglobin, carbohydrate, and/or adenosine triphosphate (ATP) post cleaning, as well as for for microbes post HLD/sterilization, to verify the cleaning and HLD/sterilization processes. Washburn and Pietsch,12  who performed testing for ATP, protein, and microbial growth after manual cleaning and again after HLD, identified correlations in protein detection at both stages (i.e., if manual cleaning did not remove the protein residue, neither would HLD). An extensive study by Ofstead et al.13  added visual inspection using a borescope to test for protein, ATP, and microbial contamination. In addition to residue, the researchers also noted scratches and staining on interior surfaces. They then allowed a seven-day growth period for microbial samples that resulted in contamination (microbial growth) in 60% of the endoscopes sampled.

Figure 1.

Flushing one of the many channels of an endoscope with sterile water, followed by passing air through the channel with a syringe, is a time- and labor-intensive process.

Figure 1.

Flushing one of the many channels of an endoscope with sterile water, followed by passing air through the channel with a syringe, is a time- and labor-intensive process.

Regarding microbial surveillance, a detailed description of standardized microbial testing techniques is provided through the International Association of Healthcare Central Service Materiel Management certification lesson on microbial surveillance of flexible endoscopes.14  Although not yet required, the lesson highly recommends conducting microbial surveillance.

Also of note, in the case of cleaning verification, methods for extraction of samples are far from efficient and are highly susceptible to contamination by various inadvertent actions committed by those conducting the extraction, potentially leading to false-positives. Conditions of transport, hand off from clinical areas to SPDs and within different areas of the SPD, and failure to use or change gloves have been shown to cause incidents of contamination.5 

Ribeiro and de Oliveira15  performed microbial testing of air/water channels and reported widespread contamination. They found that some air/water channels are too narrow to brush; thus, physically reaching all areas of all channels is not possible. The air/water channel is the narrowest channel in endoscope design; it is smaller than the biopsy channel through which most of the therapeutic work is done during endoscopic procedures. Presumed to hold less contamination risk due to its function, the air/water channel generally receives less attention in IFUs; however, researchers identified microorganisms, including Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae, present within the channel. They posited that cleaning methods failed to fill the channel with cleaning fluid. Contamination rates were greater using the flush-brush-flush technique, which provides more friction than other collection methods.

These findings are echoed in a three-year study that used three different sampling methods, including a conventional sterile water flush (without brushing), flush-brush-flush, and a method that involved using a peristaltic pump to force sterile water through the channel to collect a sample for microbial testing.16  The higher-friction methods, with brushing and pump-assisted sampling, yielded a higher number of positive-growth samples.

TFF as a Method for Sampling and Cleaning

TFF technology is a novel closed-loop system developed for sample extraction of lumened medical devices. Sohn et al.17  described this technology as an efficient, new method that can be used to collect samples for cleaning verification and microbial surveillance of endoscopes. It uses a mixture of air under pressure with sterile water. This mixture is passed through the endoscope channels at a predetermined flow rate. The turbulent flow creates sheer force with air pressure and water movement, thereby making bubbles and droplets of random size. The water droplets (under high and variable velocity) impact the inner surface of the channels, thereby removing the adhered contaminants. TFF is produced by an apparatus that mixes the incoming regulated compressed air and sterile water, generating a turbulent mixture of the two phases.

The TFF device is connected to an endoscope using tubing for sample extraction. The residual contaminants in the channels are removed by using the mechanical force created by the water droplets under pressure. TFF is introduced as a robust technology for sample extraction, as it effectively removes the organic contaminants and bacteria in the long, narrow channels of endoscopes.

For SPD staff, the TFF device can replace the labor-intensive sampling methods described previously, any of which present inherent human performance challenges and opportunities for use error. The FDA duodenoscope surveillance protocol, which calls for two staff members to sample the endoscopes, is complex and labor intensive.18  Using only a few pieces of equipment, TFF offers a process that can be completed by one staff member in a relatively short amount of time. Without the TFF setup, endoscopes can be awkward to handle while performing the extraction.

New, commercially available equipment for transport, handling, storage, and drying (e.g., dedicated carts with bins for damp transport from procedure areas, dollies for hanging endoscopes safely and aiding in drying) can improve workflow in SPDs (Figure 2). TFF, combined with thoughtfully chosen items for handling and storage, can open the door for improved sampling and responsible microbial surveillance, while simultaneously relieving some of the ergonomic challenges and human factor issues of endoscope processing experienced by SPD staff. Improved channel flushes can provide better samples for cleaning verification and microbial surveillance of flexible endoscopes.

Figure 2.

A small and portable TFF-generating apparatus mounted on an endoscope dolly and connected to an endoscope to enable sampling.

Figure 2.

A small and portable TFF-generating apparatus mounted on an endoscope dolly and connected to an endoscope to enable sampling.

Testing TFF Efficacy

In their study introducing TFF for microbial sampling, Sohn et al.17  inoculated microorganism samples (P. aeruginosa, Enterococcus faecalis, and Candida albicans) into the channels of new endoscopes. When samples were drawn from these endoscopes using TFF, after cleaning and HLD, the samples yielded high percentages of these microorganisms compared with samples drawn using a conventional flush or flush-brush-flush method (Table 1).

Table 1.

Comparison of the results of microbial testing for endoscopes inoculated with colony-forming units (CFU) of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans samples. Sampling was performed with and without turbulent fluid flow (TFF). The extraction efficiency was higher with (98.4–99.9%) than without (83.7–97.5%) TFF. Table used with permission of Sohn et al.17 

Comparison of the results of microbial testing for endoscopes inoculated with colony-forming units (CFU) of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans samples. Sampling was performed with and without turbulent fluid flow (TFF). The extraction efficiency was higher with (98.4–99.9%) than without (83.7–97.5%) TFF. Table used with permission of Sohn et al.17
Comparison of the results of microbial testing for endoscopes inoculated with colony-forming units (CFU) of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans samples. Sampling was performed with and without turbulent fluid flow (TFF). The extraction efficiency was higher with (98.4–99.9%) than without (83.7–97.5%) TFF. Table used with permission of Sohn et al.17

Although the inclusion of surveillance sampling adds to the already challenging processes in the SPD, improved sampling and reliable cleaning verification will validate processing protocols. A sampling method that produces as little physical and mental strain as possible on SPD technicians would be beneficial in this busy environment. TFF is a closed-system approach with a high-efficiency yield for the extraction rate of both residual clinical soil and microorganisms from endoscope lumen. By using an endoscope dolly (e.g., EndoDolly; Healthmark, Fraser, MI) that holds endoscopes and allows them to hang properly, TFF eliminates the need for two people performing extractions on larger gastrointestinal scopes. The automated delivery of sterile water and air at a predetermined rate and time eliminates the human factor challenges that are inherent with the current sampling methods. Moreover, the closed-loop system reduces cross-contamination from the environment and technicians. TFF thus offers an option for improving sampling for cleaning verification and microbial surveillance.

Conclusion

Reusable endoscopes, and the diagnoses and treatments they facilitate, save lives. Cleaning these devices, however, is a difficult task. If human factors can be understood as the relationship of humans, their environment, and the tools and equipment they use, then processing endoscopes presents a unique set of challenges to that relationship. The studies discussed in this article examine the current processing procedures in a new way, calling into question the practice of laying blame for processing failures on SPD technicians. As pointed out by Hildebrand et al.9  and Jolly et al.,4  fixing humans is not the solution. Better products and processes are needed.

In August 2019, the FDA published a safety communication calling for healthcare providers to begin to transition to a new design of duodenoscopes, with removable, disposable caps for easier, more complete cleaning.19  This represents needed efforts to improve device design. Whether through improvements in processing, cleaning verification, shifting to sterilization, or even storage, novel methods of interpreting this relationship are needed. Current issues with methods of endoscope cleaning, surveillance, and verification, as detailed in the studies cited here, must be addressed with a sense of urgency.

Acknowledgments

The authors thank Seo Yean Sohn (NovaFlux Inc., Princeton, NJ), Michelle J. Alfa (University of Manitoba, Winnipeg, Canada), Richard Lai (NovaFlux Inc.), Yacoob Tabani (NovaFlux Inc.), and Mohamed E. Labib (NovaFlux Inc.) for use of Table 1.

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Author notes

Jahan Azizi, CBET, BS, is a special projects manager at Healthmark Industries in Fraser, MI. Email: jazizi@hmark.comCorresponding author

Miranda Gavette, BS, is a research and development laboratory lead at Healthmark Industries in Fraser, MI.

Kaumudi Kulkarni, MS, MSc, is a senior manager of research and development at Healthmark Industries in Fraser, MI.

Mary Ann Drosnock, MS, CIC, CFER, RM (NRCM), FAPIC, AAMIF, is director of clinical education at Healthmark Industries in Fraser, MI; cochair of AAMI ST/WG 84; a fellow of AAMI; and a member of the BI&T Editorial Board.