Main Article: Comparative assessment of the effects of process parameters as well as of detergents on PTFE channels with regard to automated reprocessing of flexible endoscopes

The cleaning of PTFE tubes or the working channels of flexible endoscopes in washer-disinfectors (EWD), especially in the limit range of the protein elimination currently considered acceptable, has hardly been studied so far. In order to test and evaluate both the cleaning effect of different detergents and different parameters of the cleaning stage, a test setup was created.

Case study: Correlation between the duration of a steam sterilisation process and the weight of the processed load

Using this setup, PTFE hose sections of 10 cm in length, each soiled with 20 μl of reactivated heparinised sheep blood and then conditioned, were subjected to the various cleaning conditions. After cleaning, samples for protein quantification were obtained by cutting the hose sections into 4–5 mm long segments and extracting them with 3 ml 1% sodium dodecyl sulphate solution by vortexing, achieving a recovery rate of 99.8%.
All the cleaners tested contained more or less enzymes. The four cleaners with a mildy-alkaline pH and a proportion of anionic surfactants provided results for the residual protein below the detection limit at 3 minutes exposure time and temperatures of 45 and 55°C, respectively. The neutral cleaner with exclusively non-ionic surfactants, on the other hand, led to residual amounts of protein, which amounted to 25 μg per test specimen on average at 35°C and to as high as 86 μg at 55°C, due to the onset of fixation. According to the acceptance criterion of 3 μg/cm² defined by the DGKH, DGSV and AKI guidline group, less than 18.9 μg residual protein would have to be achieved for the hose section. With reference to the type test, the cleaning conditions are suggested by manufacturers of RDG-E as unchangeable. However, the results of these studies show that the use of alternative cleaners and more appropriate cleaning parameters can lead to a significant improvement of the cleaning process and thus an increase in patient safety.


To date, little research has been carried out on cleaning the PTFE tubes or channels of flexible endoscopes and, in particular, there is little knowledge of the effects of various detergents or of changes made to the process parameters during the cleaning step of automated processes. The processes taking place in the flexible endoscope washer- disinfectors (EWDs) differ in accordance with the manufacturer and distributor. There are also suppliers who by invoking the type test strictly prohibit adaptation of the process parameters to the conditions prevailing at the site of use. That is incomprehensible since making such changes is absolutely normal in the case of the washer- disinfectors (WDs) used to reprocess medical devices and also include thermal disinfection. Nor does standard EN ISO 15883 support such a prohibition. In general it is unclear how the process parameters governing the cleaning steps in EWDs, in particular the conditions determining the use of detergents, were defined.

Currently, the test model specified in the Guideline for validation of automated cleaning and disinfection processes for reprocessing flexible endoscopes, compiled by the DGKH, DEGEA, DGSV, DGVS and AKI*, is used to assess the efficacy of the cleaning steps in endoscope washer- disinfectors (EWDs) [1, 2]. To that effect, the 200 cm long PTFE (polytetrafluorethylene) tubes with internal diameter of 2 mm, which are used as process challenge devices (PCDs), are contaminated with heparinised and reactivated sheep blood and eluted after cleaning with 1% SDS (sodium dodecyl sulphate) solution by means of rinsing and soaking at intervals. Sampling with the specified method should yield a protein recovery rate of at least 70% for the positive control, i.e. the PCDs with the baseline contamination load [2]. What recovery rate is assured by the described sampling method cannot be inferred from its description, nor is that made clear by the quantitative results of a field study [3]. The PCD has a baseline load of well over 25000 μg protein. For an 80% recovery rate this would mean that well over 5000 μg protein would not be recovered, which would mean a load of well over 40 μg protein/cm². That is precisely the protein-containing deposit coming into direct contact with the PTFE material. Since PTFE adsorbs significant protein amounts [4, 5] it is the removal of exactly these protein amounts that is of pivotal importance for assessment of the cleaning efficacy and is indispensable for assuring a high recovery rate. [...]

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Citation: Michels W. Comparative assessment of the effects of process parameters as well as of detergents on PTFE channels in terms of automated reprocessing of flexible endoscopes. Zentr Steril 2019; 27 (1): 52–56.

Photo: Dr. W. Michels


  1. DGKH, DEGEA, DGSV, DGVS, AKI: Leitlinie zur Validierung maschineller Reinigungs-Desinfektionsprozesse zur Aufbereitung thermolabiler Endoskope. Zentr Steril 2011; 19 (Suppl.3):1–72.
  2. Wehrl M, Kircheis U: Method for Testing the Cleaning Efficacy of Washer-Disinfectors for Flexible Endoscopes. Zentr Steril 2011; 19 (5): 357–361.
  3. Wehrl M: Control of the cleaning efficacy during performance qualification of EWD processes using test pieces according to Annex 8. Zentr Steril 2016; 24 (4): 220–225.
  4. Wie Q et al.: Wechselwirkungen von Proteinen mit Polymerbeschichtungen und Biomaterialien. Angew. Chem. 2014; 126: 8138–8169.
  5. Zardeneta G et al.: Protein interactions with particulate Teflon: implications fort he foreign body response. J Oral Maxillofac Surg 1996; 54 (7): 873–878.
  6. Guideline compiled by DGKH, DGSV and AKI fort he validation and routine monitoring of automated cleaning and thermal disinfection processes for medical devices. Zentr Steril 2017; 25, Supplement (5th Edition)
  7. Guideline for Validation of Manual Cleaning and Manual Disinfection of Medical Devices. Zentr Steril 2013; 21, Supplement
  8. Martiny H: Überarbeitung der ISO TS 15883-5 – Was erwartet uns? Vortrag DGSV-Kongress 2018, Fulda
  9. Kromidas S: Validierung – wozu eigentlich? Aseptica 2004; 10 (1): 3.
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