by P. Sagourin, A. Viallet, R. Batista, D. Talon
Intuitive Surgical recommends a complex process for cleaning da Vinci robotic instruments. The aim of this study is to validate the cleaning process used in our establishment by demonstrating the absence of residual protein. In-process tests and destructive tests were conducted with two residual protein tests: Clean-Trace® and One Life Detect ® tests. During in-process testing none of the Clean-Trace tests (n = 25) revealed the presence of residual protein. In the destructive tests (n = 15), six Clean- Trace tests demonstrated the presence of residual protein. With the One Life Detect kit all the instruments (n=15) presented blue spots corresponding to traces of protein residues. In-process testing is conducive to validating our cleaning process. However, destructive tests show protein residues in inaccessible areas.
Since March 2018 robotic procedures have been carried out in various specialties, urology, gynaecology, digestive and thoracic surgery, in our establishment using a da Vinci XI® surgical robot manufactured by Intuitive Surgical. Robotic instruments are reusable medical devices. These devices are reprocessed in the operating room (OR) and reprocessing unit for medical devices (RUMED) primarily to prevent the transmission of infectious agents. Reprocessing starts with a predisinfection and a cleaning step which is essential because effective sterilisation can only be achieved for clean instruments. Robotic instruments are of complex design. They consist of a casing with two irrigation ports, a shaft and a distal end with a double-jointed system accommodating various instruments such as forceps, needle holders or scissors (Photo 1). Due to this complex design the recommendations by Intuitive Surgical for predisinfection and cleaning entail a large number of manipulations that to a certain extent are dependent on the staff member executing them. It is therefore necessary to verify the absence of residual soils at the end of the cleaning process. The aim of this study was to validate the cleaning process for the robotic instruments used in our establishment by demonstrating the absence of residual proteins at the end of the process. Both the external and internal instrument soils were taken into account.
Materials and Methods
The cleaning method for robotic instruments used in our establishment follows the three-step procedure recommended in France by Intuitive Surgical (Table 1): predisinfection in the OR, manual cleaning in the RUMED and automated cleaning in the instrument washer-disinfector (WD) (Figure 1). Predisinfection conducted in the OR comprises immersion for 15 minutes in a disinfectant detergent based on quaternary ammonium (Anios’Clean Excel D®), with manual brushing of the joints and irrigation of Port No. 1. This is followed by rinsing with irrigation of the two ports with a water pistol. Following this predisinfection, the instruments are returned to their baskets and trays for transport in cabinets to the RUMED. The manual cleaning protocol used in the RUMED comprises the same steps used for predisinfection, i.e. immersion for 15 minutes in the same disinfectant detergent based on quaternary ammonium (Anios’ Clean Excel D) and rinsing. The instruments are then placed on a special cleaning module allowing irrigation of the two ports. A special two-hour cycle is executed in a Getinge 88 turbo washer. It comprises two cleaning steps with a special enzymatic detergent Aniosyme DLM Maxi® at a concentration of 0.5% (12 minutes, 55°C), thermal disinfection for 5 minutes at 90°C and drying for 45 minutes at a temperature above 80°C in accordance with the joint recommendations of the firms Getinge, Anios and Intuitive .
The instruments tested in our study were chosen in accordance with two parameters: frequency of use and representativeness of different categories of instruments. Hence, cleanliness was evaluated on the basis of five types of instruments: monopolar curved scissors, needle holder, Prograsp forceps (grasper), bipolar maryland forceps and bipolar fenestrated forceps (Table 2). It should be pointed out that staplers were not included in our study because their switchover to single use is being currently investigated by Intuitive Surgical. Two types of residual protein detection tests were used: the 3M Clean- Trace® test and the One Life Detect® kit. These tests have already been used to validate cleaning of different categories of instruments with an internal lumen such as orthopaedic motors as demonstrated by F. Stordeur  or osteosynthesis implants as shown by C. Lambert . The Clean-Trace test consists of a swab mounted on a stick, a ready-to-use reagent solution and a hydrating solution. Sampling is done with the swab, after hydration, by rubbing it on the surface to be analysed. It is then activated on coming into contact with the reagent and heated in a water bath for 15 minutes at 55°C. The test is read out on removal from the water bath. It is a semi-quantitative test based on the biuret reaction (or BCA method), a colorimetric reaction following oxidation of the protein peptide bonds by Cu2+ ions. The Cu+ formed binds with bicinchoninic acid forming a violet complex. According to the manufacturer’s interpretation manual, the test results can therefore present as different shades of colour ranging from green for a negative test (no protein residue) to violet for a positive test (with protein residues) through grey for an inconclusive test result (traces of protein residues) (Photo 2). The sensitivity of this test is 50 μg. The method was validated by the following: repeatability tests (five samples taken on the same day from a monopolar curved scissors at all sampling time points); reproducibility tests (five samples taken on different days from monopolar curved scissors after cleaning in a WD); positive controls (five instruments sampled on leaving the OR before predisinfection); negative controls (five swabs immersed in sterile water); and interference tests with the predisinfection liquid (five swabs immersed in the predisinfection liquid).
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The One Life Detect kit consists of three successive baths: a stain, a developer and a rinsing bath. The instruments are immersed successively in each of solutions: staining solution (5 minutes), developer solution (2 min- proutes) and rinsing water. The test is read out on removal from the rinsing bath. For each test the method is validated by positive and negative controls. Its sensitivity is 75 μg/cm2. The test is based on a colorimetric reaction with Coomassie blue taking place after formation of protein residue bonds. The blue spots attest to the presence of protein residues. While it is possible to evaluate the size and intensity of the spots, this is based on subjective criteria dependent on the interpretation of the individual staff member. We therefore chose to focus exclusively on the presence of spots on the various component parts of the distal end of the instruments, i.e. the jaws or one of the two pulleys (Photo 3).
Two types of tests were performed: in-process tests and destructive tests. The in-process tests were carried out with functional instruments ready for dispatch to the OR after reprocessing. They were performed with the Clean- Trace tests and able to demonstrate the presence of external soils. Sampling was done by RUMED personnel at sampling time points 1, 2 and 3 of the cleaning process (Figure 1). The sampling sites A, B and C on the external surface (Photo 4) were rubbed with the same swab at each sampling time point. The destructive tests were performed on instruments which had reached the end of their service life and had been returned to us by the OR management. Hence, the quantity and choice of instruments were determined by the respective specialty. The instruments were destroyed by removing the casing and sheath to access the instrument interior. The Clean-Trace and One Life Detect tests were used. Sampling was performed by RUMED staff at sampling time point 3 of the cleaning process (Figure 1). For the Clean-Trace tests the sampling sites D and E on the internal surface (Photo 5) were rubbed with the same swab at the sampling time point. For the One Life Detect test kit the entire distal end was immersed in the different baths.
In the in-process tests five instruments from each category were tested, i.e. 25 instruments in total. For each instrument a sample was taken after each step of the cleaning process (sampling time points 1, 2 and 3 of Figure 1). In total, 75 Clean-Trace tests were interpreted: 25 tests following predisinfection, 25 tests following manual cleaning and 25 tests on removal from the WD. Following predisinfection 22 tests were positive (presence of protein residues), three were inconclusive (traces of protein residues) and none was negative (absence of protein residue). Following manual cleaning four tests were positive (presence of protein residues), eight were inconclusive (traces of protein residues) and 13 were negative (absence of protein residue). On removal from the WD none of the tests was positive (presence of protein residues), three were inconclusive and 22 tests were negative (Figure 2). There was no difference between the test results obtained for the different categories of instruments regardless of sampling time point 1, 2 or 3 (analysis of variance, p>0.5). In the destructive tests, 15 instruments that had reached the end of their service life were returned to us from the OR and were destroyed for analysis: five needle holders, two scissors, five Prograsp forceps, two bipolar maryland forceps and one bipolar fenestrated forceps. Of the Clean-Trace tests performed on the dismantled instrument after removal from the WD, six were positive (presence of protein residues), five were inconclusive (traces of protein residues) and four were negative (Figure 3). With the One Life Detect kit all instruments (n=15) demonstrated blue spots attesting to the presence of protein residues (Photo 6). The spots were identified in the region of the pulleys (11/15), jaws (9/15) and the remainder of the instrument body (12/15) (Figure 4).
In this study three consecutive cleaning steps were carried out under standard instrument reprocessing conditions in an operating room (OR) and a RUMED. The first manual cleaning step (predisinfection) was performed immediately after the surgical procedure and had the advantage of preventing drying of the residual soils on the distal end and within the internal lumens of the robotic medical devices. The second manual cleaning step was undertaken in the RUMED and was followed by cleaning in the WD and thermal disinfection. Hence, the cleaning conditions differed from those reported in studies by Michels  who carried out cleaning in an ultrasonic bath followed by cleaning in the WD. In the study cited there was no predisinfection immediately after the surgical procedure. In the study by Saito  there appears to have only been a manual cleaning step and cleaning in an ultrasonic bath but no cleaning in the WD. Besides, the method we used reflects real-life use conditions as well as those under which reusable, robotic medical devices are reprocessed in a RUMED, whereas Michels  worked under laboratory test conditions using an artificial instrument test soil and protein or blood solutions.
The study by Saito , on the other hand, was conducted under real-life use conditions and involved collection of the contaminated instruments after a surgical procedure. The protein load was measured before the tests but few details are given of the conditions under which cleaning was carried out. In the Michels study  the ultrasonic bath used in conjunction with cleaning in the WD permits proper cleaning while dispensing with manual cleaning for non-cautery instruments. For cautery instruments manual cleaning continues to be needed before cleaning in the ultrasonic bath and in the WD. In the Saito study  manual cleaning used in combination with cleaning in an ultrasonic bath does not allow complete elimination of residual proteins. It must therefore be borne in mind that it is impossible to completely eliminate instrument contamination by means of manual cleaning as recommended by the manufacturer or by means of the ultrasonic baths used by Saito. In the present study no proteins were detected (or only slight traces) in the in-process tests with the Clean-Trace tests. Our cleaning process comprising three steps (two manual cleaning steps and cleaning in the WD) appears to be valid. However, the destructive tests showed protein traces in the instrument regions inaccessible to the brushes and the swabs in the cleaning steps and when sampling with the Clean- Trace swabs (jaws, pulleys). These traces of protein were detected in particular when using the One Life Detect test kit. Likewise, the Clean-Trace tests used on the internal surface identified traces of protein. The cleaning method used under standard instrument reprocessing conditions in the RUMED does not appear to be adequate.
With regards to the internal soils detected with the Clean-Trace tests, we wonder about the presence of a substance that might interfere with the tests, producing a positive result. For example in the study by Wehrl  only forceps that had been reprocessed at least three times were taken into account to prevent interference with substances lingering from the manufacturing process. However, we point out that the forceps used in the destructive tests had reached the end of their service life and will have therefore undergone more than three reprocessing cycles. Destructive tests with a new forceps would enable that hypothesis to be put to the test. As regards the residual soils detected on the instrument cables, pulleys or contact regions, we speculate about the transfer of soils towards the distal ends when moving the cables and pulleys. It would therefore appear that the standard cleaning method recommended by Intuitive Surgical is inappropriate. Indeed, the twofold manual cleaning step implies that the procedure is dependent on the staff member executing it. That is why it is necessary to conduct training for OR and RUMED personnel. Automated cleaning involving movement of the cables and internal pulleys could be effective but currently cleaning is performed only with manual procedures (no procedure using state-of-the-art automated equipment has been standardized). There appears to be a need for either equipment that will activate the wheels/rollers at the instrument ends or for single-use instruments.
No residual soils were detected on the distal ends of the different instruments after the three cleaning steps in the OR and RUMED. By contrast, in the destructive tests residual soils were identified in internal, inaccessible regions of the instruments despite the very time-consuming procedures employed in the OR and RUMED, as recommended by Intuitive Surgical. In view of the complexity of the cleaning method required, it is necessary to develop sterile, single-use robotic instruments.
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Corresponding author: Pauline SAGOURIN, Hôpital TENON Pharmacie, Bâtiment Cassiodore 4 rue de la Chine, 75020 Paris, France firstname.lastname@example.org
Conflict of interest: All authors confirm that there is no conflict of interest according to the guidelines of the International Committee of Medical Journal editors (ICMJE).
Citation: Sagourin P., Viallet A., Batista R., Talon D. Validation of the cleaning method for da Vinci XI robotic instruments using protein residue tests. Zentr Steril 2021; 29 (1): 48–53.
Manuscript data: Submitted: 24 July 2020 Revised version accepted: 31 August 2020
This article was originally published in ZENTRALSTERILISATION issue 1.2021 (Zentr Steril 2021; 29 (1): 48–53).
A letter to the Editor referring to this article was published in ZENTRALSTERILISATION issue no. 2. Dr. Michels states that 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. ++ Read the letter here. ++