This study made no use of human subjects or individual patient data and thus is exempt from seeking approval of an institutional review board. No funding was received, directly or indirectly, from any commercial or for-profit entity. It was not possible to involve patients or the public in the design, or conduct, or reporting, or dissemination plans of our research.

This study assesses the potential human public-health impact from climate change of processes included in one usage of reusable versus single-use fURS. The analysis had two stages. First, we performed a single-center life cycle assessment (LCA), according to internationally accepted methods (ISO 14040/44) [20,21,22] to estimate the Global Warming Potential (midpoint) and the potential public health impact (endpoint) of the inputs and outputs from the product system of single-use versus reusable fURS due to climate change. Second, we performed sensitivity analyses to assess how the results change when the input variables and/or modeling assumptions change.

Life cycle assessments evaluate potential impacts to the environment and human health across the entire life cycle of a product or service [20, 21]. The scope of this study was to assess and compare the potential human public health impact of single-use and reusable ureterorenoscopes used at the university medical center the University Hospital of Tübingen regarding climate change aspects. Given that studies have shown that both devices have identical clinical effectiveness and risk for the patients, our unit of analysis for the LCA, the “functional unit”, was “per one use” for each device. The duration of one use was assumed to be one hour.

Data was collected, from 2020 to 2023, about the life-cycle stages (manufacturing, delivery, use, reprocessing/maintenance, disposal) of single-use and reusable fURS. Data were prioritized according to the following hierarchy: (1) direct statements from the companies or staff involved, (2) empirical measurements (e.g., weighing the items) by the investigators, (3) data from the literature, (4) estimates based on expert opinions. Direct statements from companies and staff were obtained through interviews (conducted on-site, online, or by telephone), email correspondence, and written survey questionnaires. Manufacturing companies were contacted for data on the production of fURS, and other companies were contacted as needed for information relevant to the other phases of the life-cycle.

Electricity for manufacturing is highly dependent on the location. For single-use fURS made in China, we used Chinese electricity market data. The estimated value on the amount of electricity was confirmed by another manufacturing company. For reusable fURS made in Germany, the conventional German electricity mix listed in the ecoinvent database (ecoinvent version 3.8; Zurich, Switzerland [23]) was used.

For instance, water impacts also depend on the location. For single-use production abroad, background data for “tap water (Rest-of-the-World)” was used. For reusable fURS, European Union tap water was included in the calculation. Sensitivity analyses confirmed that even wildly implausible higher estimates of water usage had no noticeable effect on the results.

External emission parameters linked to ureteroscopy (e.g., anesthetic gases or electricity needed for air conditioning or heating the operating room) were not included in the LCA, as they were assumed to be identical for reusable and singleuse devices. We focused exclusively on the fURS itself.

Reprocessing of reusable fURS takes place at the institutional sterilization unit, a facility certified according to DIN EN ISO 13,485. We proposed data from the literature [17] to the reprocessing managers, who confirmed it as an estimate. The manufacturers of the washing machines (INNOVA E3s CMS DC GL washing and STERRAD® 100NX ALLClear sterilization) used in reprocessing were unable to provide data, so we assumed 9.2 kW/cycle (equivalent to 7.89 kWh), as also reported in a previous study for the Olympus ETD4 sterilization machine [17]. At the university medical center of Tübingen, reprocessing is performed using electricity from 100% renewable sources.

Reusable fURS require periodic maintenance, which is performed at the manufacturing company. We assumed the packaging for maintenance to be similar to the packaging for reprocessing. We assumed transportation to be similar to the transportation to and from the production company to the hospital. We added to this the impact of one reprocessing instance (packaging excluded because already included separately).

For reusable fURS reprocessing, we assumed two devices per washing machine and sterilization process. Although non-standard reusing of single-use devices has been researched on in other countries [24], we didn’t consider reusing single-use devices in our study.

When the devices are no longer usable, they are disposed of in accordance with hospital standards. Ureterorenoscopes are classified as waste code 18 01 04 [25], which designates waste for which no special requirements apply to collection and disposal. All waste treated under this code is incinerated at the local residual waste plant. Corresponding incineration processes from ecoinvent cut-off were taken to account for the impacts from disposal. To date, fURS are disposed as waste without recycling, and we assessed that a recycling option wouldn’t change the results noticeably.

The data collected served as the basis for estimating the potential health impacts due to climate change per one use of the devices, using the ecoinvent life cycle database, applying the midpoint impact assessment ‘climate change’ method as well as the mid-to-endpoint factors for human health-related climate change impacts of ReCiPe2016 [26]. The potential human health impacts are reported in disability-adjusted life-years (DALY) and were quantified based on the midpoint results as described for ReCiPe2016 (referring to De Schryver et al. (2009)) [27], considering increased risk of health damages due to climate change (1 malnutrition, malaria, diarrhoea and flood risk).

DALYs are the key measurement unit for assessing public health, combining years of life lost to early mortality with the portion of life-time lost due to living in variable states of disability from various illness [28,29,30]. In LCA, DALYs are used to standardize the potential impacts of environmental burdens.

For example, as part of the reprocessing of reusable fURS, a 20 ml Luer Solo Inject Syringe is used to flush the scope. The package of this syringe weighs approximately 1.28 g and consists mainly of plastic. One syringe is used per fURS. The material was matched with the reference “market for extrusion, plastic film| extrusion, plastic film| Cutoff, U– GLO” (U = Unit process; GLO = global) in ecoinvent. Results were added to the calculation.

LCA results are subject to assumptions and estimations. To test the robustness of the results, we performed sensitivity analyses on the parameters that were likely to affect the final results. These included four scenarios: (1) different production countries (and thus different energy sources) for the single-use fURS, (2) a different energy mix for use of the fURS at the hospital, (3) a different number of uses of the reusable fURS during its lifetime, (4) a different frequency of repairs of the reusable fURS. The variables of these sensitivity analysis are described further in the Results.