Validity of the efficacy of the spray flushing cleaning method in flexible endoscope reprocessing

Abstract

The advancement in endoscopic technology and techniques has increased its use in the diagnosis and treatment of gastrointestinal diseases. Reprocessing of reusable endoscopes remains a challenge. Inadequate reprocessing leads to bacterial contamination of the endoscope, a significant cause of endoscope-related infections. To thoroughly address the complexities of cleaning a flexible endoscope, various cleaning methods have been devised and tested across different studies. This letter evaluates one such method, spray flushing for flexible gastroscopes, developed and tested in a randomized controlled trial by Du et al. Based on the post-processing test results for this method, Du et al conclude that there is improved cleaning efficacy and reduced damage compared to manual brush cleaning. The validity and reliability of the results could be further enhanced by carefully considering the study design and a few underlying concepts that contribute to the reprocessing quality of different types of endoscopes.

Key Words: Flexible endoscope; Reprocessing; Automated spray flushing; Sampling; Blinding; Enzyme detergents; Poiseuille’s flow rate; Colonoscopes

Core Tip: The current method of cleaning endoscopes with manual brushing damages the scope channel over time. Du et al devised and tested the efficacy of a spray flushing technique in reprocessing flexible gastroscopes in a randomized controlled trial. This technique, which removes debris to a greater extent and causes less damage to the gastroscope, could significantly improve endoscope reprocessing. The validity and reliability of this study depend on several additional factors, such as sampling and blinding methods, the pressure and content of spraying, and the length and type of the endoscope. Understanding these factors is crucial for successfully implementing the spray flushing method in endoscope reprocessing practices.

TO THE EDITOR

We read the paper by Du et al[1] with great interest. The authors conducted a randomized controlled trial to test the efficacy of a novel spray flushing method in reprocessing flexible gastroscopes. The study aimed to develop an alternative cleaning method to manual brush cleaning to improve mechanical cleaning efficiency and reduce damage to the working channels. The efficiency of the spray flushing was compared against manual brush cleaning in terms of adenosine triphosphate (ATP) levels, cleanliness indicators and microbiological growth. These results showed higher cleaning efficacy of the spray flushing system as observed from the reduced damage and more significant debris removal from the gastroscope working channels.

APPLICATION OF RANDOMIZED CONTROLLED TRIAL

This study utilized a randomized controlled trial study design, which consisted of a sample size of 60 used gastroscopes (GIF-H290; Olympus, Japan) and 60 Teflon tubes (RBF4; Oupli, China) with similar properties that were randomly assigned into experimental and control groups. This study design provides an essential basis for examining the effect of an intervention on its outcome and establishing a cause-and-effect relationship[2]. The careful selection of samples comprising actual gastroscopes that had undergone examination for the measurement of ATP levels, cleanliness scores, and microbial growth reduced the influence of confounding variables in determining the quality of cleaning[3]. Random assignment of the 60 samples into two different groups, either the spray flushing (experimental) or brush cleaning (control), helps to minimize selection bias[4]. Additionally, the gastroscopes and Teflon tubes were verified to be free from damage at the beginning of the trial using borescopes to better correlate any changes in physical characteristics within the working channel due to the cleaning method utilized.

Because investigators were not blinded during the inspection of the working channels, potential detection and performance bias[5] in measuring cleanliness scores, damage scores, and microbial growth are possible. Various studies have demonstrated that the estimated treatment effect was more optimistic for studies with non-blinded assessors than blinded assessors[6]. This could lead to an overestimation of the efficacy of cleaning by the spray flushing system, as deduced from the investigators' visual inspections.

The cleanliness and damage scores used to assess the cleaning effect of the spray flushing system were derived from manual observations recorded by the same observer throughout the experiment. This study did not consider inter-observer differences, which require at least two observers for each inspection of the same sample to assess the concordance in the data from the multiple observers[7]. This study's lack of inter-observer agreement fails to eliminate observer bias. As such, this raises questions on the validity of the findings from visual inspection, including the significant debris removal and lesser damage noted in the spray flushing samples.

VALIDITY OF POST-REPROCESSING TEST RESULTS

The reprocessing quality of endoscopes is often evaluated using several indicators such as microbiological and biofilm surveillance[8], internal cleanliness, damage[9], ATP and organic residues[10]. Similarly, this study assessed the efficacy of cleaning by spray flushing and manual brushing using a mix of quantitative and qualitative indicators. Upon reprocessing the working channels, the authors measured four indicators: (1) ATP concentration; (2) Cleanliness score; (3) Microbial growth; and (4) Teflon Tube damage scores. Based on these results, there were no significant differences in the level of ATP concentration and microbial cultures obtained after spray flushing and manual brushing. Both cleaning methods produced satisfactory results within the acceptable limits according to reprocessing guidelines[11]. Significant differences were observed in cleanliness and damage scores between the spray flushing and manual brushing samples. Given the qualitative nature of the data, the lack of inter-observer agreement and the blinding of investigators, this evidence may not be substantial enough to conclude that the spray flushing system has higher cleaning efficacy than the manual brush system. Additional post-processing tests with quantitative results may be required to improve the study's validity. This could include monitoring for biofilm formation or the diversity of bacterial growth within the working channels at different sites along the tubes and time points along the experiment.

Furthermore, the study did not indicate the sampling duration for the microbial cultures. This may have contributed to the negative results of the control and experimental groups if the samples were tested for the growth of bacterial colonies before the minimum time interval requirement upon completion of reprocessing. According to the French National guidelines, a minimum of 6-hour interval between reprocessing and testing is required to allow the growth of microorganisms to an appropriate detection level[12]. The sampling site and collection frequency for the microbial cultures were also not mentioned, which could affect the count of recorded bacterial colonies. Collecting samples from different channels, such as the air-water, biopsy, and suction channels, might also give a more accurate estimate of the overall distribution of microbial cultures along the entire working channel. Different sampling frequencies have also produced different results for microbial cultures, as observed from the varying count of bacterial colonies between intermittent and continuous sampling[13]. Lastly, the samples were extracted using endoscopic forceps, which is distinct from the more standard methods of flush or flush-brush-flush techniques[14]. Incomplete extraction using forceps may result in lower bacterial colony counts.

The spray flushing system propagated the enzymatic cleaner mixed with water in each occurrence of spraying into the working channels. Conversely, in the manual brushing system, the brush can only be manually inserted to remove debris from the working channels, followed by aspirating the enzymatic detergent solution into the working channels. The use of the spray flushing device to combine the enzymatic cleaner with water is a more efficient and resourceful way to manipulate the stages in reprocessing, as it reduces a dual-step process to a single step and reduces the large reservoir of the enzyme solution to a small volume added directly to the spray flushing device[15]. However, to assess the efficacy of the cleaning method only, all other variables in the two different cleaning systems must be controlled, including the composition of the solutions used and the order of administration. Additionally, a control set-up for each cleaning method is recommended, as it would increase the study's internal validity. This can be achieved by replicating the spraying and brushing system with water instead of the solution mixture. The evaluation indicators recorded for these control setups can serve as a baseline for comparing the two systems' cleaning efficacy.

GENERALIZABILITY OF FINDINGS TO OTHER SCOPES

International guidelines recommend various practices and standards for assessing the quality of reprocessing in flexible endoscopes[16]. The wide range of endoscopes used in the clinical setting for diagnostic and therapeutic purposes poses a unique challenge for achieving optimum reprocessing quality[17]. Existing literature has shown that certain endoscopes, such as bronchoscopes, colonoscopes, side-viewing duodenoscopes, and ultrasound endoscopes, are at higher risk of contamination due to their complex design and site of contact within body cavities[18].

Although no initial scratches or residual deposits were observed within the gastroscope channels, the inner surface of the working channel still causes some friction along its length[19]. This friction can be mitigated by propelling the spraying tube within the working channels, ensuring adequate duration and contact of spraying at various channel sections. Assuming the flow rate of the cleaning solution within the spray flushing tube follows Hagen-Poiseuille’s laminar flow, several factors influence the flow rate, as detailed in Table 1. Therefore, controlling these factors in the spray flushing system throughout all 30 inspections is crucial to ensure reliable results.

Table 1 Flow rate related to Hagen-Poiseuille’s laminar flow.

Q= (πR4 ΔP)/8 μL
Q = Volumetric flow rate (m³/second)
R = Tube radius (m)
ΔP = Pressure difference across the tube (Pa)
μ = Dynamic viscosity of the fluid (Pa)
L = Tube length (m)

Poiseuille’s law also posits that a larger radius increases the flow rate. This will affect the efficacy of spray flushing among the various air/water/axillary channels of different diameters. Different endoscopes have different lengths and diameter channels compared to the standard gastroscope used in the study by Moshkanbaryans et al[20]. This further necessitates the collection of multiple samples at various points in the working channels and analyzing the results using correlation plots. These results could be used to predict the efficacy of the spray flushing method on the different types of flexible endoscopes of varying lengths and radii. As such, the efficacy of the spray flushing system tested using gastroscopes may not be generalizable to other endoscopes.

CONCLUSION

In conclusion, the overall quality of reprocessing depends on the combined efficacy of three different steps: (1) Cleaning; (2) Disinfecting; and (3) Sterilizing. The spray flushing system could be a promising cleaning method due to its potential to remove debris and reduce damage. Furthermore, spray flushing could be more cost-efficient and environmentally friendly than manual brushing methods and disposable single-use endoscopes. However, more nuanced evaluations and modifications are required to confirm the actual efficacy of the spray flushing system. Spray flushing systems should also be evaluated on other types of endoscopes before wider adoption can be advocated.