Concurrent centrifugal plasma exchange and continuous renal replacement therapy using a series–parallel circuit through a single dual-lumen dialysis catheter in severe IgA vasculitis

Abstract Background Concurrent performance of therapeutic plasma exchange (TPE) and continuous renal replacement therapy (CRRT) via a single vascular access in critically ill patients may reduce interruptions; nonetheless, this requires careful circuit design and structured monitoring. Case presentation A 74-year-old man with type 2 diabetes mellitus and cardiovascular comorbidities was transferred to our hospital for the evaluation of oliguric acute kidney injury and suspected systemic vasculitis. Skin biopsy revealed leukocytoclastic vasculitis with immunofluorescence findings indicative of IgA vasculitis. Renal function deteriorated to dialysis dependence, and intermittent hemodialysis (IHD) was initiated. On hospital day (HD) 11, CRRT was performed for acute hypoxemic respiratory failure with suspected pulmonary edema to achieve ultrafiltration with concurrent solute control; the prescribed modality was continuous venovenous hemodialysis. On HD13 and HD14, centrifugal therapeutic plasma exchange (cTPE) with fresh frozen plasma was initiated because of severe systemic deterioration and thrombocytopenia with suspected thrombotic microangiopathy. On HD13, cTPE and CRRT were performed concurrently using a series–parallel circuit via a single temporary right internal jugular dialysis catheter; no circuit-related complications occurred. Ionized calcium (iCa) was monitored at predefined sampling points. After TPE initiation, the return-segment iCa level adjacent to the patient decreased to 0.52 mmol/L at 38 min, prompting calcium gluconate infusion into the CRRT return line (10 mL/h, titrated to 15 mL/h). The patient’s iCa level remained stable intraprocedurally (1.10 mmol/L at the start and 1.13 mmol/L after completion). The last IHD session was on HD29, and renal replacement therapy was discontinued thereafter. On HD33, kidney biopsy revealed changes that were most consistent with early diabetic nephropathy with substantial chronicity, and mesangial IgA staining was weak. Given the delayed timing after intensive immunosuppression and the patient’s systemic phenotype, the biopsy results were interpreted as diabetic nephropathy, with concurrent IgA vasculitis as a clinical comorbidity, rather than as definitive active IgA vasculitis nephritis. Conclusions Concurrent cTPE–CRRT operation using a single-access series–parallel circuit was completed without circuit-related complications or bleeding exacerbation in severe IgA vasculitis with dialysis-dependent nephritic syndrome. This feasible approach may be a practical option for critically ill patients when implementing structured monitoring for electrolyte disturbances.