Green Dialysis: Let Us Talk about Dialysis Fluid

Chronic kidney disease (CKD) is one of the fastest-growing diseases and became one of the major public health problems worldwide. CKD is associated with age-related renal function decline accelerated by primary renal diseases, hypertension, diabetes, and obesity. The global prevalence of CKD is estimated on the level 13.4% of the population (stages 1–5) and 10.6% (stages 3–5) [1].

Renal replacement therapy (RRT) is the final pathway of CKD progression. Patients with renal function insufficient to sustain their life have three options to choose from hemodialysis (HD), peritoneal dialysis, or renal transplantation. The most frequent RRT modalities are extracorporeal blood purification therapies like HD or hemodiafiltration. The general concept of dialysis, described firstly by Thomas Graham in 1854 as the technique based on diffusion through the semipermeable membrane (osmosis), is still the background of blood purification. With time all elements (membranes, machines) were improved but the general principle did not change. The passage of the uremic toxins from the blood requires a constant flow of carefully and properly selected dialysis fluid. Technological progress improved all technical aspects of HD and made the treatment safe and efficient – current HD machines help us control the parameters of the treatment, and new, biocompatible filters efficiently remove uremic toxins and minimize the risk of allergic reactions. Well-educated and highly experienced medical staff make dialysis the routine medical intervention available to the majority of patients in well-developed countries. According to the ERA-EDTA registry in 2019, almost 90,000 patients have been newly included in dialysis programs in Europe. The prevalence of dialysis patients in the European Union is estimated on the level 893 per million population [2].

Extracorporeal blood purification like HD or hemodiafiltration remains the only lifesaving option for the majority of patients with end-stage of CKD. As dialysis techniques became routine in most countries, the number of treatments rapidly grow. Nowadays we can estimate that more than 600 million HD sessions are provided every year worldwide but still in some emerging countries such intervention remains a luxury for selected groups [3]. As it was estimated by Foreman et al. [4], the number of patients suffering CKD will rapidly increase and become to be the fifth reason of years of life lost (YLL) in 2040. According to the models prepared and analyzed by authors the number of YLLs caused by CKD will double in the period 2016–2040 (from 26,260,000 to 52,597,000 YLLs). On the other hand, dialysis is one of the most environment-burdening medical interventions. Hundreds of liters of water, and huge amounts of energy are consumed, and tons of medical waste are produced every year during dialysis sessions worldwide. Additionally, the most of materials (disposables, concentrates, etc.) shall be transported from suppliers’ logistics centers to the dialysis units. Considering the huge amount of materials used for HD, such topics as the cost and environmental burden (carbon footprint) of transportation should be taken into account. The growing costs of natural resources like water, and energy carriers, as well as the cost of waste utilization should influence our way of thinking regarding the optimal usage of available resources to make dialysis more environmentally friendly and cost-effective. The aim of this paper is to analyze the economical and environmental value of preparing the dialysate in centers against the usage of liquid concentrates delivered by suppliers in plastic containers. As a part of the analysis authors use the estimation of carbon dioxide amount released to the atmosphere (carbon footprint) during transportation of different formulas of dialysis concentrates. The carbon footprint as the measure of impact on the environment is widely used in different areas of human activity. Reduction of greenhouse gas emissions is one of the major ways to slow down climate change and decrease the influence of human activity on the natural environment.

As it was stated above the dialysis concept is based on the exchange of particles between blood and specially prepared dialysis fluid containing electrolytes whose composition and concentration are similar to extracellular fluid composition. Usually, the ready-to-use dialysis fluid is prepared in an HD machine from concentrates supplied by the manufacturer. HD machine mixes the concentrate with treated water in appropriate proportion to finally deliver the dialysis fluid with the desired concentration of elements. The basic composition of dialysis fluid contains sodium (Na⁺), potassium (K⁺), calcium (Ca⁺⁺), magnesium (Mg⁺⁺), chloride (Cl⁻), and bicarbonate or lactate. The concentration of elements may vary – usually, manufacturers deliver the concentrates containing 130–140 mmol/L of sodium, 1–4 mmol/L of potassium, 1–2 mmol/L of calcium, 0.5–1 mmol/L of magnesium, and 107–110 mmol/L of chloride. The bicarbonate is used as a buffer and delivered separately as the powder to dissolve by HD machine or liquid concentrate (8.4%) for dilution. In the majority of cases, preprepared dialysis concentrates need to be diluted with water in proportion 1 + 44 or 1 + 34.

In the early times of dialysis, the dialysate has been prepared in a dialysis center or hospital pharmacy by mixing elements in prescribed weight with water. As the time being, ready-to-use dialysis fluid formulations became to be more popular, and displaced dialysate prepared from separate components. Currently, there are available three options for delivery dialysate on the market – the liquid concentrated delivered in plastic containers (bags or canisters), powder for dilution with treated water or semidry concentrates delivered in returnable barrels.

The usage of canisters or bags of different volumes (usually from 4 L to 10 L, some suppliers offer 300 L barrels to be connected to the central system of concentrate distribution) is the most popular solution in dialysis centers. The main advantage of such a solution is a possibility to use dedicated and most fitted dialysate for every single patient. On the other side, it raises a number of logistic problems. The containers (with different compositions) need to be stored in the dialysis center, carried by staff, and connected to an HD machine. Also, the storage and utilization of used containers raise additional issues – empty containers have to be stored, and picked up by the supplier for reuse or to be disposed of.

Powder for dissolving is usually delivered in carton boxes containing 25 kg of powder, for the preparation of 100 L of dialysis concentrate (1 + 34) to be delivered directly to HD machines. For the preparation of the ready-to-use liquid concentrate, special mixing devices are needed. One of such device is Granumix^® manufactured by Fresenius Medical Care or Renosol system marketed by B.Braun. The main advantages of using powder concentrates are smaller (even 60%) storage space needed and lower weight of goods [5]. The preparation of concentrate should be done by trained personnel who will be responsible for the proper dilution of the powder and checking the quality of the ready-to-use solution. Preparation of 100 L concentrate takes usually 20–30 min (depending on water temperature). Usually, ready-to-use concentrate is prepared by a technician one time a week and stored in the storage tanks located in the WTU room. On the own calculation and data collected from dialysis centers basis, the optimized dialysis center uses 3.2 L of 1 + 34 concentrate, one portion (25 kg) of powder will cover the need for 31 dialysis sessions and may replace 10 containers of liquid concentrate (112 kg). From a yearly perspective, the mid-size dialysis center (treated 90 patients) will use 453 carton boxes with powder (11,325 kg) or 4.493 of 10 L containers of liquid concentrate (50,321 kg).

The most modern systems developed by dialysis equipment manufacturers are fully automated mixing systems based on semidry concentrates which are delivered in ready-to-connect to the mixing device barrels and produce 750 L 1 + 44 liquid concentrates in the dialysis center. Such systems are delivered by B.Braun (EcoMix) or Fresenius Medical Care (Granumix Plus). In the case of Fresenius Medical Care system, semidry concentrate (Diamix) is delivered in returnable barrels on a four-wheel trolley. A full Damix barrel contains 349 kg of semidry concentrate to be connected to Granumix Plus (mixing device), which takes the substance from the barrel, adds the right amount of water, and transfers the finished portion of concentrate to the storage tank. In about 1 h, 750 L of 1 + 44 concentrate is ready to use. From the storage tank, concentrate is transported via a central distribution system to dialysis machines. Depending on dialysis center needs, the system allows using three different compositions of acid concentrate at the same time. Barrels, delivered to the dialysis center are returnable and collected by the manufacturer for refilling. After the preparation of the solution from Diamix, no waste is produced that requires processing or utilization. Additionally, as the barrels are mounted on the trolley, the transportation from a concentrate storage room to the preparation room (usually connected with the water treatment room) is easy and does not require to use of significant physical force. One-time preparation of 750 L of concentrate Diamix contrary to 100 L from powder (e.g., Granudial) reduces the number of operations performed by the dialysis center technician, reducing the risk of mistakes and workload [6].

The disadvantage of such solutions which somehow limits their popularity is a necessity of investment – the system requires the installation of a concentrate distribution loop, storage tanks, and mixing devices. However, the installation of such a system during the modernization or construction of the new dialysis center is worth taking into consideration.

Dialysate consumption depends on various factors like the type of HD machine, session duration, prescribed flow, etc. To obtain the expected outcomes of dialysis sessions measured by the Kt/V indicator the proper flow rate of dialysis fluid (Qd) proportionally to blood flow rate (Qb) must be ensured. Every HD machine enables setting of the appropriate dialysis fluid and blood flow. Studies regarding the efficiency of HD conducted past years clearly showed the modest impact of high dialysis fluid flow on HD performance. Among several studies found, most of them showed no significant change on Kt/V with lower or higher dialysis fluid flow. Also, the studies on the impact of Qd change on uremic toxins clearance and patient’s outcomes showed no significant advantage of high Qd. The results of the studies mentioned above allow us to say that decreasing Qd from 500 mL/min to 400 mL/min does not worsen patient outcomes and HD performance but helps save 24 L of dialysis fluid during a single dialysis session [7, 17].

Modern HD machines are equipped with modules that automatically reduce Qd to the patient’s blood flow and minimize dialysate consumption during preparation and after reinfusion. Smart using of available options offered by manufacturers allows to save an additional portion of acid concentrate and water.

Every human activity influences the natural environment. Global warming, shortening natural resources, and the raising need for medical services create a new reality and challenges that must be taken into consideration for our future course of action. RRT is one of the most resource-consuming medical procedures. According to reports collected from Polish dialysis centers and own calculations, during every HD session, there are used more than 500 L of tap water, 7 kWh of energy, and produced more than 1 kg of medical waste. As we consider, every patient requires 156 HD session per year – the average water consumption per patient exceed 78 m³ of water and 1,100 kWh yearly. The point of contrast, the average household electricity consumption remains on the level of 900 kWh/per person/year and 117–180 L of water per person daily (43–65 m³/year) [18, 19].

The weight of concentrates to be delivered to the dialysis center is the major factor influencing the cost (financial and environmental) of transportation from the manufacturer to the final consumer. The crisis in the energy carriers market and extremely high fuel prices made the transportation cost one of the significant costs of treatment, which must be borne by the supplier and in the end influences the price of materials. The careful choice of the concentrate delivery system can improve the cost-effectiveness of dialysis.

One of the most often used parameters for assessing the impact of human activity on the environment is carbon footprint – the amount of greenhouse gas (carbon dioxide and others) emitted to the atmosphere as the effect of exact activity. Material transportation to dialysis center generates a countable and significant carbon footprint. As the concentrates are the heaviest materials to be transported to a dialysis center, the authors tried to assess the amount of carbon dioxide emission during the transportation of different formulas of concentrates to a hypothetic dialysis center. As it is shown in Table 1, the most fuel-consuming is the delivery of concentrates in small containers (10 L). For this study’s purposes, we assumed the average concentrate (1 + 44) consumption of 4 L/dialysis session or 5 L/dialysis session in the case of 1 + 34 concentrate. The calculation has been made for the dialysis center treating 120 patients on HD. The distance between the center and the supplier is 100 km and the center is supplied in concentrates 2 times a month. As 1 L of diesel weighs 835 g and contains 86.2% of carbon (720 g), combustion of the carbon to carbon dioxide needs 1,920 g of oxygen, and burning 1 L of diesel produces around 2.64 kg of carbon dioxide. For carbon footprint calculation, carbon dioxide production of 120 g CO₂/ton/km has been assumed [20].

As it was shown in Table 1, the transportation of canisters with liquid concentrates is less effective and affects the environment much higher than the transportation of dry/semidry formulation. The carbon footprint produced during the transportation of liquid concentrates can be even four times higher than the transportation of dry ones. The same remarks concern the cost of transportation as well as man work needed to unload the truck (96.6 tons vs. 23.4 tons). On the other side, powder or semidry concentrates limits the flexibility of choosing the composition of the dialysis fluids; however, in most cases 2–3 most common compositions are used for the majority of patients. Dilution of powder concentrate requires the presence of a technician during the process and a final check of the density and other physical parameters of the prepared solution.

An additional effect of the switch to dry or semidry concentrates is significantly less space for storage – in the case of using liquid fluid in 10 L containers at least 5 sqm is needed for storage. For barrels delivered two times a month storage space shrinks to 3 sqm or 2 sqm in the case of powder concentrate.

Green dialysis, meaning taking into consideration the resources used during dialysis and its impact on the environment, became more and more of a burning topic. Shortage of natural resources like water, growing costs of energy (electricity, fuel, natural gas used for heating and production of disposables), and greenhouse gas emissions associated with each step of treatment (manufacturing, transportation, waste utilization) make, otherwise noble deeds, a considerable burden on the environment. The environmental impact of dialysis therapy has been the subject of analysis by many researchers involved in RRT. Medical waste management, the cost of medical waste utilization, and the possibility of decreasing the weight of medical waste were the subjects of several publications in last years [21, 23]. Authors indicate the crucial factors for rational waste management based on the careful and proper waste separation – recyclable, neutral, and hazardous [21]. The use of appropriate functions of HD machines also allows for a significant reduction in waste weight and reduction of dialysis fluid volume needed for a treatment session [22]. The weight of disposables is also one of the factors which influence costs and environmental burden. As it was shown in the paper, the weight difference of selected dialyzers may reach 95 g – multiplied by millions of HD sessions every year worldwide makes a significant difference in waste utilization costs and decreases greenhouse gas emissions during waste incineration [23].

One of the indicators of how human activity influences the environment is the amount of carbon dioxide released into the atmosphere as a result of the activities of a particular individual, organization, or community, called a carbon footprint. Besides all limitations and difficulties with proper calculation, carbon footprint appears as the most universal indicator of climate change impacts [24]. The carbon footprint generated by dialysis was the subject of several studies conducted in Europe, Australia, Africa, and the USA [25, 29]. All authors found the sizable carbon footprint generated by dialysis centers. However, the findings from the studies differ significantly (from 24.5 to 65.1 kg of carbon dioxide) released into the atmosphere per one dialysis session, even the smallest amount presented by Connor et al. [25] is relatively high in comparison with other medical interventions. The study conducted by Seghal et al. [28] indicated a carbon footprint on the level of 58.9 kg CO₂ per treatment. Available studies on carbon footprint estimation differ in scope, factors, and approach. Despite all limitations of such studies, authors agree on the significance of RRT’s carbon footprint. Carbon dioxide emission may be significantly reduced by healthcare providers through smart and reasonable management of resources (energy, water), investment in modern HD machines and water treatment systems as well as proper planning of patients’ transportation and waste management.

Absolutely crucial in the green dialysis concept is proper water management. Water used for HD must be preprepared by a water treatment system (WTS) with reverse osmosis (RO) module which guarantees the ultrapure fluid for use in extracorporeal RRTs. Reverse osmosis (the heart of the water treatment system) is the process of filtration of the water under high pressure through a semipermeable membrane with pores that allow water molecules to pass through. Bigger particles (organic or inorganic particles, bacteria, etc.) cannot pass the membrane. RO is an extremely effective process for obtaining the required quality of water but due to its’ physical nature has a very important disadvantage – the massive volume of wastewater usually removed to drain. During passing through reverse osmosis, even 75% of water is treated as waste and simply lost [29]. The modern solutions working in properly designed and constructed WTS allow to a decrease in the volume of waste to 50–60%, however, still the amount of lost resources is frightening. The volume of wastewater depends on several factors which should be taken into consideration on the very early stage of WTS design. The pretreatment process with well-calculated gravel, activated carbon, and softener columns parameters improve the water quality before the reverse osmosis process. The next factor influencing the waste volume is the temperature of the water passing through RO – in general, high temperature increases product flow and low temperature decreases the water flow [30]. The problem of what to do with rejected by reverse osmosis water is still the subject of discussion and publications and seems to be extremely important in the green dialysis concept [29, 36]. The simplest solution seems to reuse the rejected water again in the reverse osmosis loop. Such a solution, however, tempting as the cheap and relatively easy-to-arrange concept, has several limitations. First and most valid is the fact that water rejected in the RO process contains concentrated contaminants. Passing the wastewater again through RO will increase the concentration of impurities and finally, we get a highly concentrated (even toxic) solution to be disposed of [31]. A very interesting concept is using the rejected water for household purposes – flushing the toilets, watering gardens, lawns as well as using for central sterilization or other hospital wards [29, 33]. Usage of rejected water requires additional storage tanks for rejected water, a pumping system and an appropriate water supply system to end devices. Apart from the waste generated in the reverse osmosis process, a significant part of the water removed and discharged into the sewage system is a dialysate with dissolved uremic toxins. Tarrass et al. [37] presented the novel idea of using HD wastewater as the source of phosphorus and nitrogen for soil fertilization. According to their study, currently in the pre-proof stage of publication, 95% of PO₄³⁻ and 23% of NH₃⁺ can be recovered from used dialysis wastewater and the business case appears to be profitable. Such an idea, if confirmed in future investigation may be an interesting concept in line with the “zero-waste” approach.

Acid concentrates became a more significant cost item of the HD session. The increasing cost of fuel, manpower, and water forces a change in behavior and challenges the consequences of routine procedures. Among the three available options of supplying HD center in concentrate – liquid concentrate in canisters or bags, semidry or dry powder delivered in barrels or carton boxes, the last two options seem to be the most environmentally friendly and help save limited resources (storage space, workload). Environmental costs of transportation are not without significance – transportation of ready-to-use liquid concentrate generates even four times higher carbon footprint in comparison with other options.

The medical community should be particularly sensitive to environmental issues and try to limit the impact of its activities on the state of the environment. It is highly recommended to rethink some common rules – e.g., dialysate flow, investment in the modern system of concentrate production in the center, reduction of a number of concentrate compositions. Every small step toward reducing the impact of our activities on the environment multiplied by the number of medical procedures performed can be a big step for the whole of humanity.

J.Z., W.M., and T.P. are the employees of Fresenius Medical Care. The authors J.S.M., M.P., P.Z., and J.M. have no conflicts of interest to declare.

No funding was received for this study.

J.Z. and J.M. were involved in data analysis/interpretation, contributed to drafting the manuscript and revised its final version, contributed to the conception and study design, data acquisition, analysis, data interpretation, and manuscript drafting. J.Z., T.P., W.M., M.P., J.S.M., P.Z., and J.M. contributed to data acquisition. All authors gave final approval of the submitted manuscript.