Letter to the editor: Validation of the cleaning method for da Vinci XI robotic instruments using protein residue tests

Letter to the Editor from: Dr. Winfried Michels, Prüflabor DWM, Kasseler Tor 20, 34414 Warburg, Germany, on: P. Sagourin, A. Viallet, R. Batista, D. Talon: Validation of the cleaning method for da Vinci XI robotic instruments using protein residue tests. Central Service 2021; 29 (1): 48–53. Read the main article here.


The authors cited my publication in Central Service 2017; 25 (6): 375–381, stating that they conducted their tests under the real- life reprocessing conditions of a RUMED, whereas (allegedly) my work was performed under laboratory test conditions using an artificial instrument test soil and protein or blood solutions. That is not correct because my tests comprised both laboratory tests with heparinised sheep blood, rendered coagulable through the addition of protamine sulphate immediately before application as a test soil, and investigations in a RUMED with instruments harbouring real-life soils. The laboratory test results were confirmed by the RUMED investigations.

The authors did not achieve satisfactory results with their cleaning efficacy tests. That concords somewhat with the findings reported in the publication by A. Maurin et al. in Central Service 2020; 28 (6): 344–350. Both groups of authors used the product Anios’Clean Excel D® for disinfectant precleaning. Since thorough, effective precelaning is crucial for the cleaning results achieved in the automated washer-disinfector, it is also quite possible that this product is not suitable for cleaning these robotic instruments. The formulations used in such combination products for cleaning and disinfection regularly compromise the cleaning efficacy.

In view of the low sensitivity of the residual protein detection methods used, and the heavy protein load identified, one must also ponder whether false positive test results occurred. For example, the destructive test results obtained on using the BCA method are alarmingly poor. It should be urgently clarified whether small amounts of metallic abrasion were transferred from the tungsten wires with the swab into the BCA reaction solution. Because of its position in the electrochemical series, tungsten reduces copper(II) and the copper(I) formed gives rise to a false positive result through complex formation with bicinchoninic acid. Tests should also be conducted to clarify whether the Coomassie blue method produced false-positive blue colorimetric reactions because of adsorbed surfactants.


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