A Proof of Concept Study, Demonstrating Extracorporeal Carbon Dioxide Removal Using Hemodialysis with a Low Bicarbonate Dialysate

Source abstract

Extracorporeal carbon dioxide removal (ECCO 2 R) devices remove CO 2 directly from blood, facilitating ultraprotective ventilation or even providing an alternative to mechanical ventilation. However, ECCO 2 R is not widely available, whereas dialysis is available in most intensive care units (ICUs). Prior attempts to provide ECCO 2 R with dialysis, by removing CO 2 in the form of bicarbonate, have been plagued by metabolic acidosis. We hypothesized that bicarbonate dialysis is feasible, provided the plasma strong ion difference is maintained. We used a mathematical model to investigate the effects of bicarbonate removal on pH and CO 2 in plasma, and performed in-vitro experiments to test CO 2 removal using three dialysates with different bicarbonate concentrations (0, 16, and 32 mmol·L −1 ). Our modeling predicted a reduction in partial pressures of CO 2 (PCO 2 ) and increased pH with progressive lowering of plasma bicarbonate, provided strong ion difference and plasma proteins ( A tot ) were maintained. In our in-vitro experiments, total CO 2 removal, scaled up to an adult size filter, was highest with our dialysate containing no bicarbonate, where we removed the equivalent of 94 ml·min −1 (±3.0) of CO 2 . Under the same conditions, our dialysate containing a conventional bicarbonate concentration (32 mmol·L −1 ) only removed 5 ml·min −1 (±4; p < 0.001). As predicted, pH increased following bicarbonate removal. Our data show that dialysis using low bicarbonate dialysates is feasible and results in a reduction in plasma PCO 2 . When scaled up, to estimate equivalent CO 2 removal with an adult dialysis circuit, the amount removed competes with existing low-flow ECCO 2 R devices.