A proof of concept study, demonstrating extracorporeal carbon dioxide removal using hemodialysis with a low bicarbonate dialysate

Extracorporeal carbon dioxide removal (ECCO ₂R) devices remove CO ₂ directly from blood, facilitating ultraprotective ventilation or even providing an alternative to mechanical ventilation. However, ECCO ₂R is not widely available, whereas dialysis is available in most intensive care units (ICUs). Prior attempts to provide ECCO ₂R 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 ₂R devices.