CaCl2-Citrate Regional Anticoagulation with Continuous Veno-Venous Haemodialysis Leads to Unwanted Chloride Loading Compared to Continuous Veno-Venous Hemofiltration with Systemic Anticoagulation

Introduction: Chloride transfers during continuous renal replacement therapy (CRRT) have not been adequately described and may differ based on CRRT technique. We aimed to measure chloride mass transfer (J<sub>S,Cl</sub>) during CRRT and identify associated determinants. Methods: We performed a two-centre, prospective, observational study in France and Australia in ICU patients with CRRT initiated for <24 h. Patients received continuous veno-venous hemofiltration (CVVH) or continuous veno-venous haemodialysis (CVVHD, with citrate-CaCl<sub>2</sub> regional anticoagulation). Over a 24 h period, plasma and effluent chloride concentrations were measured every 4 h to compute chloride mass transfer (J<sub>S,Cl</sub>, in mmol.min-1) using a modality-specific model, with negative value indicating chloride transfer towards the patient. Secondary outcomes were the identification of CRRT settings associated with J<sub>S,Cl</sub> (using multivariate mixed effects regression). Results are presented with median (interquartile range). Results: Between February 2021 and August 2022, we enrolled 37 patients (64 [56–71] years, 67% male), for a total of 20 CVVHD and 20 CVVH sessions. Over 24 h, plasma chloride concentrations were significantly higher, and J<sub>S,Cl</sub> significantly lower during CVVHD, compared to CVVH (−0.10 [−0.33 to 0.15] vs. 0.01 [−0.10 to 0.13] mmol.min-1, p < 0.05). With both modalities, net ultrafiltration (Q<sub>UF</sub>NET) and plasma chloride concentrations were the principal determinants of J<sub>S,Cl</sub>, with higher Q<sub>UF</sub>NET being associated with an increase in J<sub>S,Cl</sub> during CVVHD. Also, CVVHD sessions demonstrated a concentration gradient between the plasma and the effluent chamber of −6 [−9 to −4] mmol.L-1. Finally, CaCl<sub>2</sub> reinjection during CVVHD accounted for 35% [32–60%] of total J<sub>S,Cl</sub> in sessions with a negative J<sub>S,Cl</sub>. Conclusion: Compared to CVVH, CVVHD with regional citrate anticoagulation was associated with greater chloride mass transfer to the patient and higher plasma chloride concentrations. This was due to high dialysate chloride concentrations and CaCl<sub>2</sub> reinjection. This effect could only be controlled by high net ultrafiltration flow rates.