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Abstract: PO0807

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

Session Information

Category: Trainee Case Report

  • 000 Coronavirus (COVID-19)


  • Lee, Tung Lin, Singapore General Hospital, Singapore, Singapore
  • Liew, Zhong Hong, Singapore General Hospital, Singapore, Singapore
  • Kaushik, Manish, Singapore General Hospital, Singapore, Singapore
  • Ng, Li Choo Michelle, Singapore General Hospital, Singapore, Singapore
  • Wong, Jiunn, Singapore General Hospital, Singapore, Singapore
  • Choong, Hui-Lin, Singapore General Hospital, Singapore, Singapore
  • Tan, Han K., Singapore General Hospital, Singapore, Singapore

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 heparin-bonded 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.


Attenuation of circuit lifespan was observed despite adequately dosed RCA and heparin bonded oXiris filters. We theorize that this could be due to a pro-coagulant 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.