Introduction:
Chronic kidney disease affects almost 10 percent of the world's population in the age groups of 65 to 74. The incidence of end-stage renal disease (ESRD) differs in different parts of the world. 60 percent of people affected with ESRD are on hemodialysis, 30 percent on functioning transplanted kidneys, and the other 7 percent on peritoneal dialysis.
What Is the Prevalence of End-Stage Disease?
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Across the world, end-stage renal disease has been increased.
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End-stage kidney disease, also called kidney failure, happens when chronic kidney disease undergoes a gradual loss of kidney function and reaches an advanced state.
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In end-stage renal disease, the kidneys stop functioning and face difficulty meeting the body's needs.
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The prevalent renal replacement therapy in India is hemodialysis, followed by transplantation (more liver-related), and peritoneal dialysis is the third most opted option.
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An ideal renal replacement therapy impersonates the complexity of the human kidneys and maintains a person’s quality of life.
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Artificial kidneys are a part of renal replacement therapy and can be recreated in clinical settings.
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With end-stage renal disease, a person requires either a kidney transplant or dialysis to stay alive.
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In India, the leading cause of chronic kidney disease and end-stage renal disease is diabetes and hypertension.
What Are the Limitations of the Existing Renal Replacement Therapy; Hemodialysis?
Although hemodialysis is the most prevalent form of renal replacement therapy, after initiation of dialysis, the survival rate of people on hemodialysis is only 50 %. The weight of current existing dialyzers is more than 60 kilograms which is heavy, and they require an immense amount of water (more than 120 liters) and power supply. These reasons can act as barriers towards home dialysis, interfere with the patient's routine life, and decrease the quality of life.
In comparison to the continued functioning of healthy kidneys, hemodialysis has several limitations. It only removes a fraction of uremic toxins, and large fluctuations can occur in the internal environment, including fluid overload and depletion due to the intermittent dialysis schedule. The most common schedule of hemodialysis includes four hour dialysis, thrice a week.
What Are the Limitations of the Existing Renal Replacement Therapy; Peritoneal Dialysis?
Even though peritoneal dialysis offers a continuous form of dialysis, the clearance of uremic toxins in peritoneal dialysis is lower than in hemodialysis. Due to the peritoneal membrane damage caused due to increased glucose concentrations of dialysate, which is required for peritonitis and osmotic clearance of toxins, the median life span on peritoneal dialysis is only 3.7 years.
What Are the Limitations of the Existing Renal Replacement Therapy; Transplantation?
Even though transplantation is the best form of renal replacement therapy, it is limited by a demand-supply mismatch. Almost 12 patients die waiting for transplantation daily. It also has a lifespan of around 10 to 20 years, after which the patient has to restart their dialysis and wait for another transplantation.
What Are Portable and Wearable Artificial Kidneys?
Dialysis miniaturization and portability will help in patient freedom and improve the quality of life. It has the potential for more continuous and frequent dialysis with better toxin clearance, less fluid fluctuation, and improved clinical outcomes. The various portable and wearable devices are under development and are not currently available for commercial use.
A few types of artificial kidneys include:
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Portable Artificial Kidney (PAK) - The first-generation kidney weighed around 10 to 25 kilograms and the second-generation kidney weighed around 1.5 to 10 kilograms. NeoKidney, Fresenius PAK, Medtronic PAK, and EasyDial are under development. All of these are portable, some are in suitcase form and some can be used for home-based dialysis.
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Wearable Artificial Kidney (WAK) for Hemodialysis - The wearable artificial kidney is a device that weighs less than 5 kilograms and is designed in such a way that it can be worn as a vest or a belt. It requires only 400 milliliters of water and is driven by batteries. Its components include pumping systems, dialysate regeneration systems, dialysis membranes, batteries, and patient monitoring systems for blood leaks and air bubbles. The success factor of wearable artificial kidneys is the availability of safe vascular access.
For a wearable artificial kidney, due to the frequent use by the patient, arteriovenous fistula and grafts are not ideal as there are chances of dislodgement of needles which can result in complications. Subcutaneous port devices and chronic venous catheters with a lower flow are likely solutions in such a case. The proof of concept was established when seven patients were recruited for 24 hour dialysis using a wearable artificial kidney. Patient satisfaction rates were reasonable, no adverse hemodynamic changes were noted and the target ultrafiltration rates were achieved.
3. Wearable Artificial Kidney (WAK) for Peritoneal Dialysis (PD)- Compared to conventional peritoneal dialysis, it has the potential for better clearance of toxins with a more continuous dialysate flow, less damage to the peritoneal membrane, and lesser chances of peritonitis due to the decreased in bad exchange and given less exposure to glucose. The devices that are under development for wearable peritoneal dialysis are:
(i) Carry Life System for PD- This is a wearable, continuous-flow peritoneal dialysis system containing replaceable sorbent cartridges.
(ii) Automated WAK for PD- This is a wearable, tidal flow peritoneal dialysis system working on a modified recirculating dialysis sorbent technology. Before returning to the peritoneum, the regenerated dialysate is supplemented with electrolytes and glucose. Animal studies revealed toxin clearance except for phosphate clearance and adequate ultrafiltration. The cartridge component needs a replacement every seven hours.
(iii) Wearable Artificial Kidney (WEAKID project)- This is a multicenter collaboration designed for an eight-hour nighttime tidal flow dialysis with a cartridge that is optional for daytime dialysis.
(iv) Vicenza WAK for PD - This is a continuous flow peritoneal dialysis system. A study done in 2007, showed a lack of a urea clearance system with deposition of fibrin in the sorbent cartridge and no provision for bicarbonate and glucose administration. No other studies have been done so far.
4. Wearable Artificial Kidney Using Electro-Deionization - Using electro-deionization, the United States Kidney Research Corporation reported a dialysate-free, novel waterless, and cell-free system. To replicate the glomerular and tubular functions, nanofiltration, ultrafiltration, and reverse osmosis are combined with electro-deionization. Animal studies were successful but human trials are awaiting.
Conclusion:
The future of artificial kidneys is exciting and is fast changing. Wearable or portable replacement therapy is being developed but is not yet available in routine clinical practice. In the coming decade, it is predicted that interrelated therapies like enhanced dialysis, portable artificial kidneys, and wearable artificial kidneys will be available for clinical use to improve the patient center management and outcomes in end-stage renal disease and chronic kidney disease.
