Ionic homeostasis, acid-base balance and the risk of citrate accumulation in patients after cardiovascular surgery treated with continuous veno-venous haemofiltration with post-dilution regional citrate anticoagulation – An observational case-control stud

Background: Patients after cardiovascular surgery, requiring renal replacement therapy, can benefit from adequate non-heparin circuit anticoagulation. Simplified regional citrate anticoagulation (RCA) protocol proposes the use of citric acid dextrose formula A (ACD-A) during post-dilutional continuous veno-venous hemofiltration (CVVH) with standard bicarbonate buffered calcium containing replacement solution. Citrate accumulation diagnosed upon total to ionized calcium ratio (tCa/iCa) and low ionized calcium (iCa) are considered as the biggest risks related to regional citrate accumulation. Methods: This prospective observational case-control study evaluated electrolyte and acid-base homeostasis in cardiovascular surgery patients treated with post-dilution CVVH with a simplified RCA protocol with ACD-A. In total, 50 consecutive cardiovascular surgery patients were evaluated. Base excess, pH, bicarbonate, lactate, Na+, Cl-, Mg++, and inorganic phosphate concentrations, the total to ionized calcium ratio (tCa/iCa), and high anion gap metabolic acidosis were assessed during haemofiltration treatment in survivors and non-survivors. Results: Thirty-three (66%) patients died. The therapies were very well balanced in sodium and chloride homeostasis. The lactate concentration and anion gap decreased during CVVH sessions lasting longer than 72 hours, but no inter-group difference was observed. The tCa/iCa ratio exceeded 4.5% and was significantly higher in non-survivors (p=0.037). Initial lactate concentration did not correlate with tCa/iCa ratio during haemofiltration. Magnesium and phosphate concentrations decreased and additional supplementation with magnesium was necessary. The magnesium concentration was lower in the non-survivors. Conclusions: The incidence of citrate accumulation exceeded 4% and was significantly higher in non-survivors. Supplementation with magnesium and phosphate ions is needed in CVVH with RCA.