Thursday, November 10, 2011

Wearable Artificial Kidneys (WAK): a new paradigm in renal care


Since the advent of renal replacement therapies, there has been a need to make the therapy more physiologic and improve the self care of the patient. Shifting to longer and daily hemodialysis and attempts to take the therapy away from the hospital and involve patients in self treatment have been proposed to improve the quality of dialysis and also quality of life. Advances in medical technology, manufacturing and nanotechnology have brought out many advances. The development of miniaturized and wearable dialysis systems are probably the next generation of RRT short of a fully “implantable artificial kidney”.
These systems include miniaturized versions of all the components of a conventional dialysis set up which can be worn by the patients and thus provide 24 hours “CRRT”. These systems are only in trial phases and are an exciting field of research.

There are few types of these devices developed:
1.       WAK-wearable artificial kidney (miniaturized hemodialysis system)
2.       WUF- wearable ultrafiltration systems.
3.       WAKMAN system (see Figure)- this is the name given to the prototype WUF to be used in patients with congestive heart failure.
4.       Vi WAK- Vincenza WAk-this is a system that is used with CAPD which recirculates two of the long day and night cycles continuously, regenerating the PD fluid extracorporeally. It reduces the number of cycles and the quantity of PD fluids used.
5.       CARPEDIEM-pediatric dialysis system, a fallout of the miniaturization research. It can be used to provide dialysis to infants and children (body weight 2-10 kgs)
Technical aspects and challenges of wearable kidneys:
  •  Good access providing adequate blood flow (100ml/min), these accesses and the other circuitry should use biocompatible materials that are non-atherogenic.
  •  Minimal priming volume.
  • Remote control systems.
  • The dialyzer reduced in size down to one tenth of the normal dialyzers. It should provide a clearance in the range of 20 ml/min with ultrafiltration rates not higher than 5 ml/min. In one of the studies published, the WAk system achieved a weekly Kt/V of 6 which is more than in case of a thrice weekly conventional hemodialysis.
  •  The entire system should be powered by long lasting batteries so that there is no need of an external power source.
  •   Minimal amount of dialysate (500 cc) that is regenerated by a separate system.
  • The entire system should be small and wearable and should not hamper the patients movement and activities of dialysis living.
Source: Claudio Ronco et al. Nefrologia 2011;31(1):9-16

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