The acu-men: a new device for continuous renal replacement therapy in acute renal failure

Flow balance optimization and fluid removal accuracy with the Quanta SC+ hemodialysis system

BACKGROUND

Fluid management is integral to hemodialysis, both to correct abnormalities in a patient's plasma composition and to maintain fluid balance. Consequently, accurate net fluid removal during treatment is a critical design element of hemodialysis machines. As dialyzers have evolved, with increased ranges of ultrafiltration coefficients available, it has become more challenging for dialysis machines to minimize errors in flow balance and net fluid removal.

RESEARCH DESIGN AND METHODS

This paper describes the design, evaluation and experimental performance of the flow balance and ultrafiltration module of the SC+ system to deliver clinically specified fluid removal with both passive and active control measures, in laboratory conditions designed to simulate a wide range of therapies.

RESULTS

The use of passive and active control allows the errors to be minimized across a wider dynamic range of conditions. For the SC+ system, the average flow balance error was 1 mL/hr with an SD of 19 mL/hr and with ultrafiltration it was 13 mL/hr and an SD of 20 ml/hr across all conditions.

CONCLUSIONS

This paper demonstrates that the SC+ hemodialysis system, a small, simple and versatile CE marked device, operates within the limits required by international standards across a wide range of experimental conditions.

Development of an accurate fluid management system for a pediatric continuous renal replacement therapy device

Acute kidney injury is common in critically ill children, and renal replacement therapies provide a life-saving therapy to a subset of these children. However, there is no Food and Drug Administration-approved device to provide pediatric continuous renal replacement therapy (CRRT). Consequently, clinicians adapt approved adult CRRT devices for use in children because of lack of safer alternatives. Complications occur using adult CRRT devices in children because of inaccurate fluid balance (FB) between the volumes of ultrafiltrate (UF) removed and replacement fluid (RF) delivered. We demonstrate the design and validation of a pediatric fluid management system for obtaining accurate instantaneous and cumulative FB. Fluid transport was achieved via multiple novel pulsatile diaphragm pumps. The conservation of volume principle leveraging the physical property of fluid incompressibility along with mechanical coupling via a crankshaft was used for FB. Accuracy testing was conducted in vitro for 8 hour long continuous operation of the coupled UF and RF pumps. The mean cumulative FB error was <1% across filtration flows from 300 to 3000 ml/hour. This approach of FB control in a pediatric-specific CRRT device would represent a significant accuracy improvement over currently used clinical implementations.

Technical breakthroughs in the wearable artificial kidney (WAK)

BACKGROUND

The wearable artificial kidney (WAK) has been a holy grail in kidney failure for decades. Described herein are the breakthroughs that made possible the creation of the WAK V1.0 and its advanced versions V 1.1 and 1.2.

DESIGN

The battery-powered WAK pump has a double channel pulsatile counter phase flow. This study clarifies the role of pulsatile blood and dialysate flow, a high-flux membrane with a larger surface area, and the optimization of the dialysate pH. Flows and clearances from the WAK pump were compared with conventional pumps and with gravity steady flow.

RESULTS

Raising dialysate pH to 7.4 increased adsorption of ammonia. Clearances were higher with pulsatile flow as compared with steady flow. The light WAK pump, geometrically suitable for wearability, delivered the same clearances as larger and heavier pumps that cannot be battery operated. Beta(2) microglobulin (beta(2)M) was removed from human blood in vitro. Activated charcoal adsorbed most beta(2)M in the dialysate. The WAK V1.0 delivered an effective creatinine clearance of 18.5 +/- 3.2 ml/min and the WAK V1.1 27.0 +/- 4.0 ml/min in uremic pigs.

CONCLUSIONS

Half-cycle differences between blood and dialysate, alternating transmembrane pressures (TMP), higher amplitude pulsations, and a push-pull flow increased convective transport. This creates a yet undescribed type of hemodiafiltration. Further improvements were achieved with a larger surface area high-flux dialyzer and a higher dialysate pH. The data suggest that the WAK might be an efficient way of providing daily dialysis and optimizing end stage renal disease (ESRD) treatment.