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

Abstract

Background: Patients with known or new-onset acute renal failure after cardiovascular surgery, requiring renal replacement therapy, can benefit from adequate non-heparin circuit anticoagulation. The idea behind not using heparin relates to the post-operative risk of bleeding. 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 study evaluated electrolyte and acid-base homeostasis in cardiovascular surgery patients with known chronic or new-onset acute renal failure treated with post-dilution continuous veno-venous haemofiltration (CVVH) with a simplified RCA protocol with ACD-A. In total, 50 consecutive cardiovascular surgery patients treated with CVVH with RCA 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. In total, 235 haemofiltration sessions with a median circuit survival time of 57 hours (1-117) were evaluated. The therapies were very well balanced with regard to sodium and chloride homeostasis. The lactate concentration and anion gap decreased during CVVH sessions longer than 72 hours, but no inter-group difference was observed. The tCa/iCa ratio exceeded 2.5 in 11 of 246 (4.5%) readings and was significantly higher in non-survivors (p=0.037). No correlation was observed between the lactate concentration before haemofiltration and the tCa/iCa ratio during haemofiltration. Magnesium and phosphate concentrations decreased during CVVH, and additional supplementation with magnesium was necessary. The magnesium concentration was lower in the non-survivors.Conclusions: The CVVH RCA protocol provides stable sodium and chloride concentrations and a tendency towards higher pH values and bicarbonate concentrations. Supplementation with magnesium and phosphate ions is needed. The incidence of citrate accumulation exceeded 4% and was significantly higher in non-survivors.Trial registration: retrospectively registered: Clinicaltrials.gov, NCT03836742.