CaCl2-citrate regional anticoagulation with CVVHD leads to unwanted chloride loading compared to CVVH with systemic anticoagulation.

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 (JS,Cl) during CRRT and identify associated determinants. We performed a two-center, prospective, observational study in France and Australia in ICU patients with CRRT initiated for < 24h. Patients received continuous veno-venous hemofiltration (CVVH) or continuous veno-venous hemodialysis (CVVHD, with citrate-CaCl2 regional anticoagulation). Over a 24h period, plasma and effluent chloride concentrations were measured every 4h to compute chloride mass transfer (JS,Cl, 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 JS,Cl (using multivariate mixed effects regression). Results are presented with median [interquartile range]. 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 24h, plasma chloride concentrations were significantly higher, and JS,Cl significantly lower during CVVHD, compared to CVVH (-0.10 [-0.33-0.15] vs. 0.01 [-0.10-0.13] mmol.min-1, P<0.05). With both modalities, net ultrafiltration (QUFNET) and plasma chloride concentrations were the principal determinants of JS,Cl, with higher QUFNET being associated with an increase in JS,Cl during CVVHD. Also, CVVHD sessions demonstrated a concentration gradient between the plasma and the effluent chamber of -6 [-9- -4] mmol.L-1. Finally, CaCl2 reinjection during CVVHD accounted for 35% [32%-60%] of total JS,Cl in sessions with a negative JS,Cl. 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 CaCl2 reinjection. This effect could only be controlled by high net ultrafiltration flow rates.

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