Dialysis: A wearable dialysis device: the first step to continuous therapy


receive haemodialysis worldwide. Although this figure suggests that haemodialysis is a successful life-supporting treatment, one only has to scratch under the surface of these data to realise that the 5-year survival in economically advantaged populations is less than that of several common solid-organ malignancies1. In addition, haemodialysis is an expensive treatment, which limits its availability to patients in economically developing countries. Haemodialysis requires a dialyzer with rapid small solute clearance through which blood and dialysate are pumped in countercurrent directions. Sessions are typically around 4 h and given thrice weekly. Due to the intermittency of treatment, patients are requested to restrict dietary intake of sodium, potassium and phosphate as well as to limit fluid intake to reduce intradialytic weight gain. During the haemodialysis session fluid that has accumulated is removed, so the most common complication during haemodialysis is hypotension. The rapid clearance of small solutes leads to changes in plasma osmolality and reverse water movement into the brain, so in addition to symptoms related to hypotension, most patients feel tired post-dialysis, and this fatigue can take minutes to more than a day to resolve2. Although some patients bene fit from home haemodialysis, the majority dialyse in dialysis centres, often having to adapt their lifestyle to fixed sessions and the time spent travelling to and from centres. Four additional pumps were required to regulate ultrafiltration flow, administer heparin for anticoagulation, and refresh the dialysate with electrolyte and sodium bicarbonate solutions. This design shows the complexity of the device. As this was a 24 h trial, it is unknown as yet whether different dialysate compositions would be required for longer treatments or for different patients. Gura et al. report the treatment of seven patients, who were connected to their wearable haemodialysis device using central venous access catheters4. Only five patients completed the 24 h treatment. Ideally this device would be worn at home, and as such the first hurdle is to establish safety. One patient stopped using the device due to circuit clotting and the other due to multiple technical problems. Two patients required battery exchanges for the blood pump. Three patients required interventions to remove air bubbles from the blood circuit, thought to have come from air left within the dialyzer during initial circuit priming. One patient needed the sorbent cartridges replaced. A common problem encountered by several patients was the presence of small bubbles of carbon dioxide that were not fully eliminated by the gas permeable chamber, which would intermittently reduce dialysate flows. As patients were allowed to move around freely, blood flow also intermittently fell due to mechanical kinking of blood lines. Problems related to blood flow and bubble formation should be overcome by Not surprisingly many patients are unable to continue with employment, and self-reported depression rates are high3. Gura and colleagues now report findings from a pilot trial of a wearable haemodialysis device4. A wearable device would potentially enable patients to move around and perform normal activities during treatment. In addition, by working 24 h a day, it would allow slower removal of both fluid and uraemic toxins, potentially reducing interdialytic symptoms and the risk of hypotension. To be acceptable to the patient the device has to be lightweight and ergonomically comfortable to wear. On the other hand the device has to operate for as long as possible, without the need to regularly replace parts5. Compared to standard haemodialysis treatment, which would typically use ~120 l of dialysate in a 4 h session, the device developed by Gura et al. uses a fixed dialysate volume of 375 ml, which then needs to be regenerated by passing through a series of sorbents and ion exchangers. As this process does not substantially remove urea, urease is added to the sorbents. This enzyme converts urea to ammonia, which is then converted into ammonium carbonate, leading to the generation of carbon dioxide6. To prevent bubbles of carbon dioxide disrupting flow in the dialysate circuit, a gas permeable section of tubing is inserted between the sorbents and the dialyzer. A battery-operated mini-pump powers blood and dialysate in countercurrent directions through a standard dialyzer. D I A LY S I S

DOI: 10.1038/nrneph.2016.100

Cite this paper

@article{Davenport2016DialysisAW, title={Dialysis: A wearable dialysis device: the first step to continuous therapy}, author={Andrew Davenport}, journal={Nature Reviews Nephrology}, year={2016}, volume={12}, pages={512-514} }