Attenuation of circuit longevity in COVID-19 critical illness with AKI on continuous venovenous hemodiafiltration despite the use of regional citrate anticoagulation (RCA) and heparin-bonded an 69 (oxiris®) filter

Introduction: Critical illness in SARS-CoV-2 (COVID-19) infection can result in acute kidney injury (AKI) Continuous renal replacement therapy (CRRT) is part of the overall supportive ICU management Case Description: CRRT was delivered as Continuous Veno-venous Haemodiafiltration (CVVHDF) using the Prismaflex (Baxter Inc ) system with heparinbonded AN69 filter (oXiris®) The filters were electively changed every 12 hours for first 5 days to augment cytokine adsorptive capacity Regional citrate anticoagulation (RCA) was used to ensure filter longevity Initial citrate dose was prescribed at 3 0 mmol/L All 3 consecutive patients were male aged 66 7 ± 6 02 years APACHE II score was 32 7 ± 6 51 and predicted mortality was 71% Mean initial creatinine was 264 7 μmol/L, and urine output was 6 7 mL/hour All patients were on vasopressor support, broad spectrum antimicrobials and mechanical ventilation 30 oXiris filters were studied in the 3 patients 6/30 (20%) filters clotted spontaneously before scheduled change Mean filter lifespan (24/30) was 689 6 ± 42 3 min before elective change For the filters that clotted, mean circuit longevity was 515 7 ± 126 2 min The observed difference was significant, p = 0 002 Importantly, filter clotting occurred despite adequate citrate dose of 3 0 mmol/L and mean post-filter ionized calcium of 0 34 ± 0 06 mmol/L Vascular access issues were excluded by review of access, return pressures Citrate dose was increased to 3 2 mmol/ L for all patients and this reduced the frequency of filter clotting subsequently Two patients were extubated and had full renal recovery - mean duration of CRRT dependence was 9 5 days However, the third patient remained CRRT dependent until demise on the 28th day of ICU stay Discussion: Attenuation of circuit lifespan was observed despite adequately dosed RCA and heparin bonded oXiris filters We theorize that this could be due to a procoagulant state induced by the SARS-CoV-2 infection Possibly, higher citrate dose to target even lower post-filter ionized calcium may be required to optimise anticoagulation and filter lifespan, thereby ensuring optimal effluent dose and solute clearance, for critically ill COVID-19 patients