INTRODUCTION: Dialysate-to-patient chloride mass transfer may occur during continuous veno-venous hemodialysis (CVVHD) with regional citrate anticoagulation (RCA). However, additional RCA-related ultrafiltration (UFRCA) and plasma chloride shifts to the intracellular compartment may impact mass transfer evaluation to an unknown extent.

METHODS: In an ancillary prospective, single-center study, we evaluated chloride mass transfer J_(S,Cl) of adult patients treated with CVVHD-RCA. Chloride concentrations were measured in the effluent, and at filter's inlet and outlet on the plasma side. J_(S,Cl) was computed as the difference in chloride mass at the filter's inlet and outlet in each compartment (i.e. dialysate and plasma water). A positive J_(S,Cl) indicated chloride mass removal from plasma water. We accounted for the additional ultrafiltration volume performed automatically by the CVVHD monitor to account for citrate and CaCl2 administered volumes. Dialysate J_(S,Cl) from the CLODICUS study (NCT04755491) were recomputed using this methodology.

RESULTS: We studied 10 patients with 18 observations. Dialysate J_(S,Cl) was significantly lower than plasma J_(S,Cl) (0.21 [0.07-0.24] vs. 0.31 [0.15-0.46] mmol.min-1, P<0.05), indicative of chloride removal from plasma water not exclusively related to loss in the dialysate compartment. Chloride removal from plasma was significantly associated with greater decreases in plasma bicarbonate along the filter (P<0.01). In the original CLODICUS study, UFRCA flow amounted to 207 [interquartile range: 172-217] ml.h-1, and the dialysate J_(S,Cl) to 0.11 [-0.01 to 0.23] mmol.min-1. Increasing net ultrafiltration flow was associated with increasing dialysate J_(S,Cl).

CONCLUSIONS: Plasma chloride mass removal during CVVHD-RCA is significantly greater than what is accounted for by dialysate-based loss, suggesting that plasma chloride is transferred to an intracellular compartment. Furthermore, to account for the online administration of citrate and CaCl2 solutions, CVVHD-RCA applies additional ultrafiltration, which significantly contributes to chloride removal from plasma water.