Extracorporeal carbon dioxide removal (ECCO2R) devices remove CO2 directly from blood, facilitating ultraprotective ventilation or even providing an alternative to mechanical ventilation. However, ECCO2R is not widely available, whereas dialysis is available in most intensive care units (ICUs). Prior attempts to provide ECCO2R with dialysis, by removing CO2 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 CO2 in plasma, and performed in-vitro experiments to test CO2 removal using three dialysates with different bicarbonate concentrations (0, 16, and 32 mmol·L−1). Our modeling predicted a reduction in partial pressures of CO2 (PCO2) and increased pH with progressive lowering of plasma bicarbonate, provided strong ion difference and plasma proteins (Atot) were maintained. In our in-vitro experiments, total CO2 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 CO2. 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 PCO2. When scaled up, to estimate equivalent CO2 removal with an adult dialysis circuit, the amount removed competes with existing low-flow ECCO2R devices.
From the *Division of Respiratory Medicine and Critical Care, Department of Medicine, National University Hospital, Singapore, Singapore
†Center for Critical Care Nephrology, Clinical Research Investigation and Systems Modeling of Acute Illness (CRISMA) Center, Department of Critical Care, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania
‡Institute of Health and Science Technology, Faculty of Medicine, Department of Nephrology Aalborg University, Aalborg, Denmark
§McGowan Institute for Regenerative Medicine, Departments of Bioengineering and Critical Care Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
Submitted for consideration March 2018; accepted for publication in revised form July 2018.
Disclosure: The authors have no conflicts of interest to report.
This work was supported by a grant from Singapore National Medical Research Council, NMRC/TA/0015/2013 (Cove). This work was supported by a grant from Singapore National Medical Research Council, NMRC/TA/0015/2013 (Cove), and in part by a NUHS-NHIC Joint MedTech Grant (NUHSRO/2017/030/NUHS-NHIC/04 (Cove).
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Correspondence: Matthew E. Cove, Division of Respiratory Medicine and Critical Care, Department of Medicine, National University Hospital, NUHS Tower Block Level 10, 1E Kent Ridge Road, Singapore 119228, Singapore. Email: firstname.lastname@example.org.