Abstract
Introduction: Fluid overload (FO) is a prevalent and serious complication of end-stage chronic kidney disease (ESRD). Its most dramatic manifestation is acute and life-threatening pulmonary edema. It is also associated with a high rate of morbidity and mortality in these patients. On the other hand, maintaining a state of hydration and optimal volume in these patients remains the major challenge of renal replacement therapies. We report an emerging technological approach to achieve “fluid neutrality” in patients with ESRD. It is a portable and intelligent ultrafiltration device called MorWAK (Moroccan Wearable Artificial Kidney). It was designed to detect, quantify, and treat daily FO using the principle of ultrafiltration through a semi-permeable membrane. Its operating principle is based on the use of accordion-shaped suction bellows, already used in surgery, as an ultrafiltration pump. The two aims of this study were to explore the functioning of the suction bellows (establishment of a mathematical equation) and to test the performance of MorWAK in vitro using bovine whole blood. Methods: The first part of the study involved measuring the pressure within the bellows as a function of the volume added after depression at the start of the experiment. The second part consisted of five ultrafiltration sessions on bovine whole blood bags. The blood pump was set to a constant flow rate of 120 mL/min. Blood pressure was kept constant, at approximately 80 mm Hg, during the five experiments by positioning the blood bag at 50 cm height. In all our experiments, we used a polyethersulfone membrane of 1 m2 and a standard suction bellows of 800 mL capacity. Ultrafiltration was compensated by concomitant controlled saline infusion. Results: The equation describing the evolution of pressure inside the suction bellows as a function of the volume it received was Pi = P0 [1 − ln (Vi)/ln (V0)]. Pi is the pressure inside the suction bellows at a time t, Vi is the volume of saline solution inside the suction bellows at the time t, P0 is the maximum depression reached during the contraction of the suction bellows, and V0 is the volume of the bellows at rest (ln: natural logarithm). In the second part of the study, the pressure inside the suction bellows had the same profile as during the previous experiment (logarithmic curve) up to the zero value (0 mm Hg). Then, it followed a linear curve parallel to the accumulation of the liquid by ultrafiltration in the suction bellows. When the blood pressure and the pressure inside suction bellows became equal, the ultrafiltration stopped. The mean final ultrafiltered volume was 854.23 ± 95.12 mL during a mean session duration of 28.33 ± 7.85 min. The mean difference between this volume and the theoretical volume calculated based on transmembrane pressure (TMP), ultrafiltration coefficient (KUF), and membrane area was 3.22 ± 0.57 mL. Conclusion: This profile is very interesting since it perfectly mimics the profiles described in blood volume monitoring systems used currently. The final prototype of the device will include tools for measuring blood density, electrodes for measuring electrolytes in the ultrafiltrate, and solute injection systems coupled with algorithms. This will allow our device to perform almost all renal replacement therapies through a telemedicine platform, aiming to improve the survival and quality of life of patients. An animal study to confirm the efficiency and the safety of our device is planned.
