Effects of different drying temperatures and times on the drying efficiency in reprocessing of flexible endoscopes

Abstract

Background:

The drying process is a crucial step in the reprocessing of flexible endoscopes. However, the optimal drying time remains inconclusive, and the impact of temperature on drying efficiency is still unclear. This study aims to provide experimental data on the optimal parameters for endoscope drying in terms of time and temperature.

Methods:

Ten gastroscopes and ten colonoscopes from a tertiary hospital’s endoscopy center were randomly assigned to different groups based on two temperature conditions (30°C and 50°C) and dried for 30 seconds, 3 minutes, 6 minutes, 9 minutes, and 12 minutes, respectively. Residual liquid was quantitatively assessed using a borescope to determine the optimal drying parameters.

Results:

A total of 200 observations were made across the temperature and time combinations. The results showed significant differences in the number of residual droplets and the drying pass rates at different times (P < 0.001). A drying time of 12 minutes achieved complete drying of the gastroscopes. Notably, after 30 seconds of drying, a significant difference was observed in the number of residual droplets between the two temperature groups (P < 0.05), with fewer droplets present at 50°C.

Conclusion:

Drying time significantly affects the drying efficiency of endoscopes, with 12 minutes being the optimal duration. Maintaining a temperature of 50°C can shorten drying time and improve efficiency.

INTRODUCTION

Drying is a critical step in the reprocessing of flexible endoscopes, as residual liquid within the endoscope lumen is closely associated with high bioburden and biofilm formation,[1,2] which can lead to disinfection and sterilization failures. The complex structure of endoscopes, including their long and narrow lumens with combined or bifurcated channels, presents significant challenges for effective drying. Multiple studies have shown that incomplete drying of endoscopes is prevalent in healthcare settings, with 42% to 95% of lumens retaining varying degrees of liquid and carrying a risk of patient infection.[3,4,5] In a report by Bajolet et al.,[6] four patients who underwent gastroscopy were infected with multidrug-resistant Pseudomonas aeruginosa due to insufficient drying of the endoscopes. Alfa and Sitter[7] found that an additional 10 minutes of air drying with a pressure gun significantly reduced the contamination and proliferation of Gram-negative bacteria on endoscopes. Consequently, the issue of hospital-acquired infections (HAIs) related to inadequate endoscope drying cannot be overlooked, and improving drying effectiveness to achieve thorough endoscope reprocessing has become a key research focus.

However, endoscope reprocessing guidelines across different countries lack consistent and clear requirements for drying methods and related parameters.[8,9] The Chinese “Technical Specifications for Cleaning and Disinfection of Flexible Endoscopes” (WS507-2016) states that drying should be performed using a pressure gun to inflate all lumens for at least 30 seconds until completely dry,[10] but it does not specify the exact drying time. Barakat et al.[11,12] conducted several studies exploring different drying time parameters for endoscopes and found that 10 minutes yielded the best results, but they did not mention the impact of temperature on drying effectiveness. Therefore, this study is the first to use a wall-mounted hot air-drying system, with temperature control, to clarify the effects of drying temperature and corresponding time parameters, aiming to improve drying methods and provide reference data for ensuring the safe reuse of endoscopes.

MATERIALS AND METHODS

Study design

This study was conducted from November 2023 to March 2024 at the Digestive Endoscopy Center of a tertiary hospital in Jiangxi Province, China. The study was exempt from review by the Institutional Review Board because it did not involve human subjects. A total of ten gastroscopes (GIF-HQ290, Olympus, Tokyo, Japan) and ten colonoscopes (CF-H290I, Olympus, Tokyo, Japan) were included in the study, and the reprocessing of the endoscopes was performed by a designated experienced cleaning and disinfection staff member. After reprocessing, the endoscopes were randomly divided into two groups based on temperature (30°C and 50°C) and dried for 30 seconds, 3 minutes, 6 minutes, 9 minutes, and 12 minutes. The drying effectiveness was observed using a borescope (Healthmark Company) with a length of 110 cm, a diameter of 1.9 mm, and a lens magnification of up to 50 times was used to record videos and images with a resolution of 800 × 800 pixels, for each endoscope, and each drying condition was observed for 10 endoscopes per group. A single-blind method was used, with two researchers trained in using the borescope jointly observing the drying effects at different temperatures and times.

Drying procedure

The reprocessing of gastroscopes and colonoscopes followed the protocol stated in the “Technical Specifications for Cleaning and Disinfection of Flexible Endoscopes” (WS507-2016), which includes pre-cleaning, leak testing, cleaning, rinsing, disinfection, final rinsing, and drying. In this study, the endoscopes entered the drying phase within 10 minutes after the final rinse, using a wall-mounted hot air drying system with temperature control. The system allows for adjustable drying temperatures ranging from room temperature to 100°C. It uses non-magnetic nickel-chromium wire heating and a triple-stage filtration system to produce clean, compressed hot air. During operation, the air gun is connected to an individual endoscope channel, with a fixed drying pressure of 0.35 MPa [see Figure 1a]. Before drying, the researchers first dried the external surface of the endoscope with a lint-free cloth, then used a drying device to blow the suction port for 5 seconds, inserted the pipe plug, and then aimed the drying device nozzle at the biopsy channel port of the operating part [Figure 1b], performing the drying operation according to the set drying temperature and time.

Figure 1.

(a) Wall-mounted hot air drying system, (b) endoscope drying operation process

Drying effectiveness detection and evaluation method

After the drying procedure, the borescope (Healthmark, USA) was immediately used for quantitative evaluation. The residual droplets inside the biopsy channels of the endoscope were observed, photographed, and recorded using a computer.[13] The number of droplets was graded using a rating scale (see results session). If no droplets were observed inside the endoscope lumen, the drying was considered qualified; if any droplets remained, the drying was considered unqualified.

Statistical analysis

After data collection, two individuals independently entered the data into Excel and cross-checked for accuracy. Data analysis was performed using SPSS 25.00 software. Non-normally distributed measurement data were described by the median (M) and interquartile range (P25, P75). The Kruskal–Wallis H test, a non-parametric rank-sum test, was used to compare the number of residual droplets. For count data, percentages (%) were used, and the χ² test was applied to compare the drying pass rates. A difference was considered statistically significant if P < 0.05. A logistic regression model was used to analyze the factors influencing the quality of endoscope reprocessing.

RESULTS

Appearance characterization of residual droplets at different drying times and temperatures

The borescope revealed that after 30 seconds of drying at both 30°C and 50°C, there were varying sizes of linear droplet aggregations within the gastroscopes and colonoscopes, occasionally causing partial occlusion of the biopsy channel [Figure 2a and b]. As drying time increased to 3–9 minutes, the lumen contained only sparsely distributed transparent or milky white droplets [Figure 2c and d]. After 12 minutes of drying, most endoscopes achieved complete dryness [Figure 2e].

Figure 2.

Visual representation of droplets in endoscope biopsy channels observed with a borescope after different drying times

Quantitative results of residual droplets

A total of 200 samples were observed, and the results showed that in both temperature groups, the number of residual droplets decreased as drying time increased, with fewer droplets in gastroscopes compared to colonoscopes. After 30 seconds of drying, a large number of droplets remained in most endoscopes, while after 3 minutes, the droplet count significantly decreased. After 12 minutes, only a few droplets were observed in the 30°C group for colonoscopes (0.00 [0.00, 0.75]), while no droplets were found in either gastroscopes or colonoscopes in the 50°C group [Table 1]. Statistical analysis showed significant differences in the number of residual droplets across different drying times (P < 0.001). After 30 seconds of drying, there was a significant difference in the number of residual droplets between the two temperature groups (P < 0.05), with the 30°C group having more residual droplets than the 50°C group [Table 1].

Table 1.

Number of residual droplets in gastroscopes and colonoscopes at different drying times and temperatures (droplets per scope)

Drying Time	30°C		50°C		Total
	Gastroscope	Colonoscope	Gastroscope	Colonoscope
30s	18.00 (13.75, 46.00)	21.00 (11.50, 30.25)	11.00 (3.25, 14.75)	18.50 (7.25, 25.50)	16.00 (10.25, 26.00)
3 min	2.50 (0.00, 5.50)	6.00 (0.75, 9.25)	1.00 (0.00, 4.25)	1.50 (0.00, 4.75)	2.00 (0.00, 7.00)
6 min	0.50 (0.00, 2.7500)	0.50 (0.00, 2.00)	0.00 (0.00, 2.00)	0.00 (0.00, 2.50)	0.00 (0.00, 2.00)
9 min	0.00 (0.00, 1.25)	0.00 (0.00, 2.25)	0.00 (0.00, 0.75)	0.00 (0.00, 2.00)	0.00 (0.00, 1.00)
12 min	0.00 (0.00, 0.00)	0.00 (0.00, 0.75)	0.00 (0.00, 0.00)	0.00 (0.00, 0.00)	0.00 (0.00, 0.00)

1. Comparison of the number of residual droplets at different drying times for gastroscopes and colonoscopes (30s vs. 3 min vs. 6 min vs. 9 min vs. 12 min): Z=109.427, P<0.001. 2. Comparison of the number of residual droplets at 30 seconds at different drying temperatures for gastroscopes and colonoscopes (30°C vs. 50°C): Z=−1.990, P=0.047

Qualitative assessment of residual droplets based on drying time and temperature

The residual droplets in the endoscopes were evaluated using a grading scale: severe, greater than 10, moderate: 5–10, mild, less than 5 After 30 seconds of drying, both temperature groups had a high proportion of severe droplet retention (>10 droplets per scope), with more than 60% of endoscopes in this category. After 3 minutes of drying, gastroscopes primarily exhibited mild (1–5 droplets per scope) or no droplet retention, while colonoscopes displayed moderate (6–10 droplets per scope) to mild droplet retention. When the drying time was extended to 12 minutes, no droplets were observed in gastroscopes, while in the 30°C group, 10.00% of colonoscopes still showed mild to moderate droplet retention [Figure 3].

Figure 3.

Graded evaluation results of residual droplets in gastroscopes and colonoscopes at different times and temperatures (Left: Gastroscope; Right: Colonoscope)

Drying effectiveness based on time and temperature

The results indicated that as the drying time increased, the drying pass rates, defined as zero droplets, improved in both temperature groups, with higher pass rates observed for gastroscopes compared to colonoscopes. After 30 seconds of drying, the pass rate for both gastroscopes and colonoscopes was 0.00%. However, after 12 minutes of drying, the pass rate for gastroscopes reached 100.00%, while the pass rate for colonoscopes in the 30°C group was still below 100%, at 80.00%. Statistical analysis showed a highly significant difference in drying pass rates across different drying times (P < 0.001), with longer drying times associated with higher pass rates. There was no statistically significant difference in drying pass rates between the two temperature groups (P > 0.05), although the 50°C group had higher pass rates than the 30°C group. No significant difference in drying pass rates was found between different types of endoscopes (P > 0.05), although gastroscopes had higher pass rates than colonoscopes [Table 2].

Table 2.

Pass rates for drying of biopsy channels in gastroscopes and colonoscopes at different temperatures and times (%)

Drying Time	30°C		50°C		Total
	Gastroscope	Colonoscope	Gastroscope	Colonoscope
30s	0 (0.00)	0 (0.00)	0 (0.00)	0 (0.00)	0 (0.00)
3 min	3 (30.00)	2 (20.00)	4 (40.00)	3 (30.00)	12 (30.00)
6 min	6 (60.00)	5 (50.00)	7 (70.00)	6 (60.00)	24 (60.00)
9 min	8 (80.00)	6 (60.00)	8 (80.00)	7 (70.00)	29 (72.50)
12 min	10 (100.00)	8 (80.00)	10 (100.00)	10 (100.00)	38 (95.00)

1. Comparison of drying pass rates at different temperatures for gastroscopes and colonoscopes (30° vs. 50°): χ²=0.981, P=0.322. 2. Comparison of drying pass rates at different times for gastroscopes and colonoscopes (30s vs 3 min vs 6 min vs 9 min vs. 12 min): χ²=88.400, P<0.001. 3. Comparison of drying pass rates between different endoscope types (gastroscopes vs. colonoscopes): χ²=1.621, P=0.203

Impact of drying time, temperature, and endoscope type on drying effectiveness

Logistic regression analysis was used to evaluate the relationship between drying effectiveness and factors such as drying time, temperature, and endoscope type. The results showed that drying time was a significant factor affecting drying effectiveness, with a statistically significant impact (P < 0.001). Extending the drying time (OR: 0.251; 95% CI: 0.176–0.359) was a favorable factor for improving drying effectiveness in gastroscopes and colonoscopes. The analysis revealed no statistically significant impact of drying temperature or endoscope type on drying effectiveness (P > 0.05) [Figure 4].

Figure 4.

Results of the multivariate analysis on factors affecting endoscope drying effectiveness

DISCUSSION

Effective drying is a critical step in endoscope reprocessing, essential for preventing microbial proliferation and ensuring storage safety.[14] Numerous studies have identified inadequate drying as a key factor contributing to endoscopy-associated nosocomial infections.[7,15] Epidemiological investigations report contamination rates of up to 80% for improperly dried endoscopes,[16] with residual fluid providing an ideal environment for microbial survival and growth. At present, manual pressure air guns are commonly used for drying across most healthcare institutions. However, the optimal duration and the impact of drying temperature remain unclear. The development of borescopes now allows direct visualization and quantification of residual moisture within endoscopic channels, offering a valuable means of assessing drying effectiveness.[13,17,18] In this study, visual assessment using a borescope revealed that complete drying of gastroscopes at both 30°C and 50°C required a minimum of 12 minutes. Notably, colonoscopes at 30°C required even longer drying times. These findings diverge from current international guidelines, which recommend a minimum drying time of 10 minutes,[9,19,20] suggesting that current standards may be insufficient to ensure complete endoscope drying, highlighting the need for further optimization of drying protocols to enhance patient safety.

Temperature regulation is a key parameter in optimizing endoscope drying protocols, as appropriate temperatures facilitate the removal of residual fluid while protecting delicate components. According to endoscope reprocessing guidelines,[9] endoscopes can tolerate temperatures up to 55°C, and drying temperatures should not exceed this threshold to prevent potential material damage. Since room-temperature compressed air remains the predominant method, this study is the first to propose drying endoscopes using a 50°C heated air gun. The results demonstrated a statistically significant difference in residual droplet counts between the two temperature groups after 30 seconds of drying (P < 0.05), with the 30°C group consistently showing more residual droplets across all time intervals. These findings highlight the indispensable role of temperature in the drying process. By incorporating a temperature-controlled hot-air system, efficient and stable cyclic drying was achieved, enhancing the clinical efficiency of endoscope drying. This study provides important evidence for establishing standardized protocols for heated-air drying of endoscopes and recommends incorporating temperature control into standard operating procedures to achieve more reliable drying outcomes. Future research should explore synergistic optimization of temperature with other parameters, such as airflow velocity and humidity, to further improve drying quality.

A significant correlation was observed between drying duration and drying effectiveness. In this study, drying for only 30 seconds was insufficient, leading to droplet aggregation and even “liquid pooling” within the biopsy channels. Conversely, extending the drying time to 12 minutes resulted in a 100% drying pass rate for gastroscopes. It is important to note, however, that this study focused exclusively on the biopsy channel, while other channels, such as air/water and suction channels, are also prone to moisture retention. Incomplete drying in these narrow lumens may facilitate biofilm formation and microbial regrowth, thereby increasing the risk of disinfection or sterilization failure.[15,21,22] Although prolonged drying improves efficacy, manual drying has notable limitations: time constraints may lead operators to shorten drying durations, and it is difficult to ensure uniform coverage across all channels.[23] A report by Liu et al.[24] further revealed that only 3.17% of institutions extended drying beyond 10 minutes, and most lacked standardized protocols for multi-channel drying. This inconsistency poses a direct threat to the safe reuse of endoscopes. Therefore, in addition to using auxiliary techniques such as compressed air or heated airflow circulation, promoting automated drying is essential to reduce human error, shorten drying time, and enhance safety.

Analysis of drying efficacy by endoscope type revealed no statistically significant differences in qualification rates (P > 0.05), and regression analysis confirmed that endoscope type was not an independent influencing factor (P > 0.05). This may be attributed to the similar material composition of gastroscopes and colonoscopes[25] as well as the limited sample size. Nevertheless, gastroscopes had fewer residual droplets and higher drying qualification rates, likely due to their shorter and narrower channels, smaller surface area, and more concentrated airflow. Hence, healthcare facilities should tailor drying parameters according to the structural characteristics of different endoscope types to ensure optimal drying across all channels. For high-risk patients or specific procedures, stricter drying standards may be required to further minimize infection risk.

This study has several limitations: (1) It was conducted at a single center and reflects the current drying practices at that institution. Multicenter studies are warranted for broader validation. (2) The study focused solely on gastrointestinal endoscopes due to clinical turnover constraints. Although no significant differences were observed between gastroscopes and colonoscopes, future studies should include duodenoscopes and endoscopic ultrasound scopes to evaluate whether specialized designs or materials impact drying performance. (3) The lumen inspection device used in this study offers the advantages of intuitive visualization and quantitative assessment of residual fluid but cannot access smaller channels such as air/water or auxiliary water channels. These narrow lumens are critical factors affecting drying performance and should not be overlooked. Subsequent research should aim to establish a comprehensive multi-channel drying evaluation system to provide more robust quality assurance for clinical practice.

In conclusion, drying time has a significant impact on the effectiveness of endoscope drying, and a drying time of 12 minutes is recommended for achieving optimal results. A drying temperature of 50°C can reduce drying time and enhance efficiency, but the drying time still needs to be extended to 12 minutes. Continuous optimization of drying methods and technological innovation are essential, and efforts should be made to develop more efficient and safer drying techniques to further improve the drying quality of all types of endoscopes. Future research should explore various endoscope drying methods and parameters to refine and standardize endoscope reprocessing procedures and guidelines.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

This work was supported by the Science and Technology Plan of Jiangxi Provincial Health and Wellness Committee(202510224); Science and Technology Research Project of Jiangxi Education Department(GJJ2200221).