Metabolic alkalosis is a frequently occurring problem during continuous veno-venous hemofiltration (CVVH) with regional citrate anticoagulation (RCA). This study aimed to evaluate the effectiveness of switching from high to low bicarbonate (HCO ₃ ⁻ ) replacement fluid in alkalotic critically ill patients with acute kidney injury treated by CVVH and RCA.

A retrospective-comparative study design was applied. Patients who underwent CVVH with RCA in the ICU between 09/2016 and 11/2017 were evaluated. Data were available from the clinical routine. A switch of the replacement fluid Phoxilium® (30 mmol/l HCO ₃ ⁻ ) to Biphozyl® (22 mmol/l HCO ₃ ⁻ ) was performed as blood HCO ₃ ⁻ concentration persisted ≥ 26 mmol/l despite adjustments of citrate dose and blood flow. Data were collected from 72 h before the switch of the replacement solutions until 72 h afterwards.

Of 153 patients treated with CVVH during that period, 45 patients were switched from Phoxilium® to Biphozyl®. Forty-two patients (42 circuits) were available for statistical analysis. After switching the replacement fluid from Phoxilium® to Biphozyl® the serum HCO ₃ ⁻ concentration decreased significantly from 27.7 mmol/l (IQR 26.9–28.9) to 25.8 mmol/l (IQR 24.6–27.7) within 24 h ( p   <   0.001 ). Base excess (BE) decreased significantly from 4.0 mmol/l (IQR 3.1–5.1) to 1.8 mmol/l (IQR 0.2–3.4) within 24 h ( p   <   0.001). HCO ₃ ⁻ and BE concentration remained stable from 24 h till the end of observation at 72 h after the replacement fluid change ( p  =  0.225 ). pH and PaCO ₂ did not change significantly after the switch of the replacement fluid until 72 h.

This retrospective analysis suggests that for patients developing refractory metabolic alkalosis during CVVH with RCA the use of Biphozyl® reduces external HCO ₃ ⁻ load and sustainably corrects intracorporeal HCO ₃ ⁻ and BE concentrations. Future studies have to prove whether correcting metabolic alkalosis during CVVH with RCA in critically ill patients is of relevance in terms of clinical outcome.