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Novel endoscope test articles were used to evaluate drying efficacy.
Alcohol flush and hanging in a cabinet was not effective for drying channels.
Preoperative inspection of endoscopic channels does not remove all residual liquid.
Ten minutes of compressed air is not always sufficient to dry all channels.
Factors impacting drying were channel specific and alcohol increased the time to dry.
Ten minutes of compressed air is not always sufficient to dry all channels.
Thorough drying of flexible endoscope channels has been identified as an essential reprocessing step. Yet, instructions are not specific on how to dry endoscopes. There is lack of data supporting efficacy of current drying practices, due to limitations in determining channel dryness.
Novel endoscope test articles were used to evaluate the effectiveness of alcohol flush and hanging in an ambient endoscope storage cabinet. Prepared test articles were hung in a storage cabinet for 5 days and visually inspected for residual liquid. The procedure for preoperative inspection of endoscopic systems was performed to determine the procedure's efficacy for removing residual liquid. Then, testing was performed to assess the impact of pressure, residual liquid type and route of air application on time to dry using compressed air.
Alcohol flush followed by hanging in an ambient storage cabinet was not effective for drying endoscope channels, and residual liquid was not completely removed after performing the steps of the preoperative inspection of endoscopic channels. The factors impacting effective compressed air drying were channel dependent. For some channels, alcohol increased the time to dry.
Endoscope drying is complex; borescope evaluation does not ensure a dry device.
This discrepancy may be due, in part, to a lack of details within the guidelines and instructions for performing some critical reprocessing steps. In particular, to prevent the outgrowth of microorganisms, drying has been identified as an essential step prior to storage, following high level disinfection (HLD) and liquid chemical sterilization processes.
Compounding the matter, real-world reprocessing settings often involve an inventory of old and new models of endoscopes, each requiring a unique set of instructions. While the importance of thorough drying is emphasized in manufacturer and guidance instructions, there remains a need for details regarding how to achieve effective drying of endoscopes, notably the internal endoscope channel systems.
In 1991, Alfa et al demonstrated that 10 minutes of compressed air applied to duodenoscope instrument channels, post HLD, was effective for preventing outgrowth of bacteria in instrument channels during duodenoscope storage.
Since then, 10 minutes of compressed air has been suggested as an effective time for drying endoscope channels, yet this overarching approach does not take into consideration factors that may affect drying, such as air pressure or the route of application of compressed air. Details on effective drying have been slow to unfold largely due to indirect and insensitive methods for evaluating dryness.
The most widely used methods for determining endoscope channel dryness are indicator paper methods and examination of the large diameter channels (ie, suction or instrument channels) using a borescope.
A borescope allows direct visualization of residual liquid within the large diameter channels but cannot fit into the narrow diameter channels of the air, water, elevator, and auxiliary water channels. As a result, most studies focus on dryness of the large diameter channels, but in several studies, biofilm or higher microbial density has been shown to be more common in the narrow diameter channels.
These studies emphasize the importance of drying and the need for alternative methods for monitoring dryness in the smaller diameter endoscope channels.
Determining dryness of narrow channels has been limited to the indicator paper method. In this method, cobalt chloride or copper sulfate impregnated paper is used to detect liquid emitted from endoscope channels during the application of compressed air, turning the paper from blue to pink or white to blue, respectively, upon contact with liquid. However, this method is indirect, and does not account for evaporation of small droplets of liquid during the compressed air application or air flow that may not be strong enough to push out all the liquid (authors’ observations using the novel endoscope model described herein). Additionally, Perumpail et al showed that the indicator paper method has limited sensitivity.
Given the limitations of detection methods and the lack of definitive drying instructions, it is not unexpected that current studies have reported that wet storage conditions are more predominant than previously recognized.
There are several drying practices that remain prevalent in reprocessing centers, regardless of the lack of data to support their efficacy. Alcohol flush and hanging in an ambient (no ventilation or directed compressed air) endoscope cabinet is a drying practice utilized in more than 50% of centers in the United States as reported in a recent survey.
Alcohol flush is widely believed to aid in the drying of flexible endoscope channels, relying on vertical hanging to drain residual alcohol. However, whether alcohol remains after storage has not been conclusively determined, particularly in the case of the narrow diameter channels. Furthermore, residual alcohol could be introduced to patients’ tissues during endoscopic procedures if not removed during the preoperative inspection of endoscopic systems (valve and channel inspections performed to check for functionality and potential blockages before procedures), reiterating the need for details on how to dry channels effectively.
In response to these concerns, novel endoscope test articles that allow direct visualization of internal channel systems were used to evaluate the effectiveness of alcohol flush and hanging in an ambient endoscope storage cabinet for drying endoscope channels. Alcohol flush was performed as directed in the manufacturer's reprocessing instructions for each type and model of test article, then the test articles were hung in an ambient endoscope storage cabinet for 5 days and visually inspected for residual liquid. The procedure for preoperative inspection of endoscopic systems was performed to determine if this procedure was effective for removing residual water or alcohol from the channel systems. Then, to gain understanding of how to remove residual liquid from the channel systems, preliminary testing was performed to statistically assess the impact of pressure and residual liquid type on time to dry each channel system. Lastly, the impact of the route of air application on time to dry each channel system was determined.
Endoscope test articles
Test articles were utilized to directly visualize channel dryness. The test articles were prepared by stripping the full endoscope of its outer sheath, fiber optics and actuation systems; only the channel systems and their external and internal connection points remained. Then, opaque channels were removed and replaced with equivalent transparent channels. The finished test articles simulate the geometry of the internal channel structure and complexity of the full endoscopes, however, the absence of the outer sheath, fiber optics, articulation system and the transparent channels allow for direct visualization inside the channels. The test articles used in this study differ from surrogate endoscope devices, previously described in ISO 15883-4 Annex C, because the surrogate devices do not represent the complexity of a full endoscope.
International Organization for Standardization International Standard 15883-4: Requirements and Tests for Washer- Disinfectors Employing Chemical Disinfection for Thermolabile Endoscopes. Geneva, Switzerland: International Organization for Standardization Copyright Office.
For example, surrogate devices do not include distal tip connections, junctions present in the insertion tube sections of the air and water channels and the junctions and connections within the light guide connector. Table 1 shows a list of the brand, model and channel dimensions of the endoscope test articles assembled for this study.
Table 1Brand, model, type, and dimensions of the endoscope test articles
L is the length of the channel. The channels were measured internally from the entrance at the control handle to the opening the furthest distance from the control handle. For the auxiliary water channel, the length was measured from the distal tip to the auxiliary screw opening. For the flowable guidewire, the length was measured externally from the distal tip to the opening on the control handle.
Olympus/ CF-Q180AL and CF-Q160AL/ Colonoscopes
3.70 × 1966.8
3.70 × 1581.8
Water (insertion section)
1.36 × 1926.7
Air (insertion section)
1.36 × 1974.8
Water (universal section)
2.30 × 1553.8
Air (universal section)
2.00 × 1621.8
Auxiliary water (insertion and universal section)
1.00-1.36 × 3478.2
Olympus/ GIF-Q160 converted to simulate a SIF-Q140/ Enteroscope
Y is the metal Y connector combining the air and water channels into a common channel.
) × 2816.7
Air (insertion section)
1.20-1.00 (after Y) × 2800.8
Water (universal section)
2.30 × 1586.7
Air (universal section)
2.00 × 1660.6
Olympus/ GF-UCT180/ Ultrasound Gastroscope
3.71 × 1514.5
3.88 × 1619.3
Water (insertion section)
1.17-1.35 (after Y) × 1462.1
Air (insertion section)
1.35 × 1481.1
Water (universal section)
2.30 × 1785.9
Air (universal section)
1.36 × 1712.9
Balloon (introduce water)
1.14 × 1539.9
Balloon (remove water)
1.14 × 1495.4
1.00 × 1530.3
ID is the inner diameter.
† L is the length of the channel. The channels were measured internally from the entrance at the control handle to the opening the furthest distance from the control handle. For the auxiliary water channel, the length was measured from the distal tip to the auxiliary screw opening. For the flowable guidewire, the length was measured externally from the distal tip to the opening on the control handle.
‡ Y is the metal Y connector combining the air and water channels into a common channel.
Final water rinse, alcohol flush, and storage of test articles
Manual final water rinse and alcohol flush steps were performed in accordance with the manufacturer's instructions for each test article. To enhance visualization of residual liquid in the channels, food-grade dye (McCormick & Company, Inc, Hunt Valley, MD) was used at a ratio of 1-part dye to 1,000-parts liquid (v/v) for water rinse (blue) and 70% isopropyl alcohol flush (red). Previous data demonstrated that dye did not affect the efficacy of drying test article channels; there was no statistical difference in drying between dyed versus not dyed liquids (see Fig S1 in Supplementary Materials).
In brief, test articles were placed in a basin with the manufacturer-issued adapters attached appropriately. Then, the directed volume of water (dyed blue) was applied to each of the channel systems using a syringe attached to the adapters. Next, the directed volume of air was drawn into the syringe and applied to each channel system through the adapters. When directed, a suction pump was connected to the light guide connector unit end of the test article to aspirate residual water from the suction/instrument channel system. External surfaces were dried with lint-free cloths and the valve cylinders and ports were dried with cotton swabs. For the alcohol flush, the test articles were processed as described above, however the directed volumes of alcohol (dyed red) and air were applied, and the aspiration step was performed only if directed for the model of the test article. Prepared test articles were hung vertically by the control handle in an ambient endoscope storage cabinet (Stanley InnerSpace Scope Cabinet, Solaire Medical, Grand Rapids, MI) for 5 days. See Figure 1 for a diagram of the procedures and orientation of the stored test articles.
Additional experiments were performed for each test article model to evaluate if there was a difference between retention of water or alcohol after hanging for 5 days. The test articles were prepared as described above, however the alcohol flush step was omitted.
Procedure for preoperative inspection of endoscopic systems
Inspection of the endoscopic systems was performed as directed in the manufacturer's instructions for use (IFU) for each model of test article, however, the steps were limited to the channel systems because the fiber optic components were removed during preparation of the test articles. The test articles were prepared as described above in Final Water Rinse, Alcohol Flush, and Storage of Test Articles (see Fig 1), stopping after either the final water rinse or alcohol flush. For inspection of the endoscopic systems, first the appropriate valves were inserted into the control handle and onto the instrument port of the test article. Then, the light guide connector unit of the test article was inserted into the imaging system control tower (Olympus Evis Exera III CV-190, Olympus Corporation of the Americas, Center Valley, PA) and the air and water supply adapter was attached to the port on the connector. The air and water settings on the imaging system control tower were set to the specifications directed in the manufacturer's IFU. Next, the suction/instrument channel system was attached, through the connector unit, to the adapter on a stand-alone suction pump (Dominant 50, Medela AG, Lättichstrasse 4b, Switzerland). Test articles with auxiliary water or a flowable guide-wire channel system were attached to an irrigation system (Genii gi4000 ESU, US Endoscopy, Mentor, OH) via the appropriate connection on either the connector unit or control handle, respectively. The manufacturer's IFU was followed to perform the inspections of channel systems: (1) flow of air through the air/water channel system, (2) flow of water through the air/water or balloon (if applicable) channel systems, (3) aspiration through the suction/instrument or balloon (if applicable) channel systems, (4) endotherapy tool inserted to determine whether there is blockage of the instrument channel, and (5) water irrigation through the auxiliary water or flowable guide-wire channel. When inspection of the channel systems was complete, the test articles were visually assessed for residual liquid (red alcohol or blue water). This experiment was repeated 3 times for each test article model, for both final water-rinsed or alcohol-flushed test articles.
Compressed air drying
The colonoscope test articles were prepared according to manufacturer reprocessing instructions as described above in Final Water Rinse, Alcohol Flush, and Storage of Test Articles, stopping after either the final water rinse or alcohol flush (see Fig 1). The colonoscope test article channels contained variable amounts of residual liquid after preparing according to the reprocessing instructions. As a result, the test articles reflected the variability encountered in a real-world setting. Compressed air was filtered through a 3-stage filter system (Sharpe Dryaire Desiccant System, Sharpe Manufacturing Company, Minneapolis, MN) and pressure was monitored with a digital pressure gauge (3D Instruments, LLC DTG-6000, WIKA Instruments, LP, Lawrenceville, GA).
Preliminary testing was performed to determine the impact of pressure and residual liquid type on time to dry each of the 3 channel systems of the colonoscope test article. Compressed air was applied with the colonoscope test article loosely coiled on the benchtop in a horizontal position using a hand/held air pistol fitted with a rubber-tipped nozzle (STERIS, SINKAC002, Mentor, OH) through the air/water cylinder and suction/instrument cylinder on the control handle, and the auxiliary water opening on the light guide connector unit. The application of compressed air was stopped when the test articles were visibly free of residual fluid in the channel system being evaluated. A full factorial design of experiments (DOE) was performed with pressure at 3 levels (5, 15, and 30 psi) and residual liquid at 2 levels (water or alcohol). The runs were randomly assigned, blocked on replicates and performed in triplicate. The results were analyzed with Minitab v.19 software (Minitab, LLC, State College, PA) using analysis of variance to determine the statistical significance of pressure and liquid on time to dry for each channel system.
Next, a second DOE was performed to compare the time to dry water from each channel system of the colonoscope test article using compressed air at 15 psi via 2 different routes of air application: compressed air directed through all the channels at once using manufacturer supplied adapters to limit air from escaping anywhere except the distal tip or compressed air directed into each channel system independently through the air/water cylinder, the suction/instrument cylinder (both cylinders are located on the control handle) and the auxiliary water inlet on the light guide connector unit, using a hand-held air pistol (STERIS, SINKAC002, Mentor, OH) without adapters attached. Compressed air was applied to the colonoscope test article while it was loosely coiled on the benchtop in a horizontal position. The runs were randomly assigned, blocked on replicates and performed in triplicate. The results were analyzed using analysis of variance to determine whether route of air application had a significant impact on time to dry each channel system.
Retention of alcohol and water in endoscope channel systems during ambient cabinet storage
Figure 2 shows the colonoscope test article after following manufacturer's instructions for final water rinse and alcohol flush, before hanging and after hanging for 5 days in an ambient endoscope storage cabinet. All 3 of the test article models contained a similar quantity of residual alcohol after performing the manufacturer directed instructions and retained most of the residual alcohol throughout the 5-day storage process. Gravity was not sufficient to drain residual alcohol from the channel systems. Alcohol retention was highest in the narrow diameter channels (ie, air/water, auxiliary water and flowable guide-wire channel systems). For test articles prepared by omitting the alcohol flush step, equivalent quantities of residual water remained before and after hanging in an ambient storage cabinet for 5 days, again predominantly in the narrow diameter channels.
Preoperative inspection of endoscopic systems
Figure 3 shows that the preoperative inspection of endoscopic systems does not remove all the water or alcohol remaining in endoscope channels after the final water rinse or alcohol flush: each trial showed some degree of residual liquid. The air pressure provided by the imaging control tower, although at the highest setting, allowed only minimal discharge of residual fluids. Therefore, the air channel system contained residual alcohol or water for all 3 trials in all 3 test article models. Each trial of the enteroscope test article's water channel system contained residual alcohol or water after inspection of the water system due to the long length of the channel system. In the colonoscope and ultrasound endoscope test articles, the water channel and balloon channel contained light blue or light red liquid, suggesting that some but not all the water or alcohol was removed, and the residual liquid was diluted by the inspection procedure. Similarly, irrigation of the auxiliary water and elevator guide-wire channels resulted in dilution of residual water or alcohol but not complete elimination. The suction and instrument channels of the 3 test article models showed very little or no remaining dyed liquids after aspiration of undyed water through the system.
Compressed air drying
Analysis of the preliminary DOE data showed that the impact of air pressure (5, 15, or 30 psi) and residual liquid type (alcohol or water) on time to dry was unique for each channel system (suction/instrument, air/water, or auxiliary water). However, for all 3 channel systems, pressure had a significant impact on time to dry for either type of residual liquid remaining (P < .0001, P = .001, and P = .018, for the auxiliary water, air/water, and suction/instrument channels, respectively). Moreover, compared to drying at 30 psi, the mean drying time for both residual liquids increased by 3- to 5-fold at 5 psi for each channel system. There was no statistical difference between drying both residual liquids at 15 versus 30 psi, however there was a trend for quicker average drying times at the higher pressure for each channel. Residual water was significantly quicker to dry compared to alcohol for the auxiliary water (P < .0001) and the suction/instrument channel systems (P = .01), but for the air/water channel system there was no statistical difference between times to dry residual water or alcohol (P = .75). The overall mean time to dry alcohol from the auxiliary water or suction/instrument channel system increased by 2- or 3-fold, respectively, compared to water. See Figure S2 in Supplementary Materials for the average times to dry channel systems at each pressure and residual liquid type.
Figure 4 shows the impact of route of air application on time to dry water from the channel systems of the colonoscope test article at 15 psi. Ten minutes of compressed air was not sufficient to dry all the channel systems whether applied through all the channels at once using adapters (Fig 4 diagram A) or applied to each channel system independently using a rubber-tipped nozzle (Fig 4 diagram B). Because air was applied to all channels simultaneously for application method A, time to dry was limited by the channel system that dried last, in this case the air/water channel system. Method A took an average of 19.6 minutes to dry all the channel systems compared to Method B, which took an average of 43.1 minutes. Again, similar to the findings in the preliminary DOE, impact on time to dry was unique for each channel system. Route of air application had a significant impact on the air/water (P = .005) and suction/instrument channel systems (P = .01), however had no impact on time to dry the auxiliary water channel (P = .113). See Figure S3 in Supplementary Materials for the average times to dry each channel system using the 2 routes of air application described above.
While flexible endoscope manufacturers’ instructions stress the importance of drying the channel systems, and may recommend alcohol as an aid for drying, the instructions do not give detailed steps on how to effectively dry endoscope channels. In this study, novel endoscope test articles that allow direct visualization of internal channel systems confirmed that alcohol flush and hanging in an ambient storage cabinet (a common drying practice
In particular, the narrow diameter channel systems (ie, air, water, elevator, and auxiliary water) showed that vertical hanging was not sufficient for removing either residual alcohol or water; there was approximately the same amount of liquid in the channels pre- and posthanging for up to 5 days. The large diameter channels have been the focus of most studies on channel dryness because borescopes cannot fit into narrow diameter channels.
indicating that the importance of drying the narrow channels is underappreciated. Indeed, in this study liquid retention was most commonly observed in the narrow diameter channel systems, reiterating the need for evaluating dryness in these channels.
Incorporating an alcohol flush is a common step in endoscope reprocessing practices primarily because it is widely believed to aid in drying endoscope channels. However, the results of the ambient storage cabinet investigation described here show that there is no difference in the amount of residual fluid remaining after hanging for 5 days whether or not an alcohol flush was performed. In addition, when using compressed air to dry the channels, the alcohol flush step increased the average time required to dry 2- to 3-fold for the auxiliary water and suction/instrument channels, respectively. While here we show that alcohol is mischaracterized as an aid for enhancing drying in endoscope channels, there are several other controversies previously reported regarding the use of alcohol in endoscope reprocessing. For example, the use of alcohol is limited in some medical institutions due to flammability risks, more specifically in conjunction with the use of cauterizing tools which are often utilized in endoscopy.
In this study, we showed that residual water or alcohol that remained after hanging for 5 days was not completely removed after performing the steps of the preoperative inspection of endoscopic channels. Both residual water or alcohol pose risks if introduced to patients’ tissues: alcohol as an irritant
Yet, eliminating alcohol flush from endoscope reprocessing steps, without the addition of detailed instructions on drying endoscope channels, may lead to controversy if microbes remain after HLD or final rinse water contains microbial contamination. While alcohol is not indicated for use as a high level disinfectant, in this case, alcohol flush may serve as an adjunctive microbiocidal measure. However, effective drying of endoscope channels has been shown to inhibit the outgrowth of waterborne pathogens, again emphasizing the need for inclusion of definitive drying instructions within reprocessing steps.
In this study we showed that the application of compressed air was necessary for effective removal of residual water or alcohol from endoscope channels, and that 10 minutes of drying was not always effective for drying every channel system. Drying is more complex than perceived, because each parameter evaluated had a unique impact on time to dry for each channel system. Air pressure had a significant impact on the time to dry each channel system when the pressure was dropped to 5 psi. The type of residual liquid had a significant impact for some channel systems. In fact, contrary to what may be expected due to the belief that alcohol aids in drying, residual alcohol reduced the efficiency of compressed air drying in the auxiliary water and suction/instrument channels. Furthermore, the impact of route of air application was unique for each channel system and only significantly affected the air/water and suction/instrument channels under the conditions tested. Increased attention should be considered for routes of air application that join the channel systems because channels with narrow diameters and complex geometries (ie, 2 channels that combine into one narrow channel, such as air/water channels) may be deprived of air flow due to back pressure created by the restriction of air flow through narrow channels, allowing the majority of air to flow through the path of least resistance (ie, larger diameter channels, such as the suction and instrument channels). This phenomenon was demonstrated in the current study by the increased time to dry the air/water channel of the colonoscope test article from 2.5 minutes, when air was applied to the channel system independently, to 20 minutes when air was applied to all the channels at once (Fig 4). These findings give insight into how to move forward with the development of optimal drying strategies and highlight the importance that one rule does not apply to all for achieving drying in the different types of endoscope channels.
This study has several strengths. First, the novel endoscope test articles used allow direct and sensitive visual detection of residual liquid in all endoscope channels, improving the ability to ascertain dryness compared to historical methods of detection. Beyond the improvement in sensitivity, the use of this model permits unique insight into the efficacy of drying endoscope channels because it allows observation of the interaction of compressed air with liquid inside channels, bringing many details surrounding effective drying to light. Because the test articles are real-world endoscopes, containing all the channel complexities of a functioning endoscope, interpretation of the results is not affected by artifacts that may arise when using surrogate devices that lack all the endoscope components. Retaining the complex components, such as the light guide connector unit and control handle, also made it possible to perform manufacturer's instructions exactly as described for processes such as final water rinse, alcohol flush and the preoperative inspections of endoscopic systems. Therefore, because the test articles contained real-world variability in the amounts of residual liquid before performing the compressed air drying experiments, the potential of introducing artifacts when analyzing significant impact factors was reduced. The ranges of drying times showed real-world variability, which singled out the most impactful factors via statistical analysis.
There are some important limitations that must also be recognized. There are areas of the endoscope test articles where residual liquid cannot be visualized directly (inside the light guide connector unit or in the control handle). Another limitation is that this study is focused on drying of the internal channel systems and does not address the importance of external drying. Future studies are necessary to develop effective external drying parameters, especially for areas where liquid can easily become trapped such as the control handle angulation knobs. Lastly, here we assessed only one drying practice, manual alcohol flush and hanging in an ambient endoscope cabinet, but there are other drying practices and drying equipment that have not been thoroughly evaluated for drying efficacy (eg, storing endoscopes in cabinets with exterior and/or channel air purge options, utilizing stand-alone endoscope channel air purge pumps then storing in an ambient endoscope cabinet, reprocessing in an automatic endoscope reprocessor with an air purge option then storing in an ambient endoscope cabinet, etc). The drying efficacy results demonstrated in this study are indicative of only the practice assessed; more studies are necessary to determine the efficacy of alternative drying practices and equipment.
In conclusion, the purpose of this study was not to provide users with detailed instructions for how to effectively dry endoscopes, but to understand the impact of various parameters on drying. Furthermore, the efficacy of drying was channel system dependent suggesting an effective drying strategy should be assessed for each endoscope model and type. The finding that alcohol flush does not shorten and, depending upon the channel system, can increase the time for compressed air drying was unexpected and adds fuel to the controversy of whether it is best practice to flush channels with alcohol prior to endoscope drying and storage. The utility of these findings may aid in establishing more detailed and definitive drying instructions in the future.
We would like to extend thanks to the following for their cooperation and support: STERIS Instrument Management Services for preparation of the endoscope test articles used in this study, Charles Pachono for producing the graphics included in this manuscript, and Agustina Vargas, from STERIS Endoscopy, for training and use of equipment used for the preoperative inspection of endoscopic systems.
International Standard 15883-4: Requirements and Tests for Washer- Disinfectors Employing Chemical Disinfection for Thermolabile Endoscopes. Geneva, Switzerland: International Organization for Standardization Copyright Office.
Conflicts of interest: Michelle Nerandzic, Kathy Antloga, and Christine Litto have no conflict of interest to disclose. Nancy Robinson has disclosed a pending patent: US Patent Application 16/542734. Title: Method/apparatus to evaluate internal flexible endoscope channels in the context of endoscope ports and channel complexities.