title: Magnesium flux during continuous venovenous haemodiafiltration with heparin and citrate anticoagulation.
abstract: OBJECTIVE
  To describe magnesium flux and serum concentrations in ICU patients receiving continuous venovenous haemodiafiltration (CVVHDF).
  
  
  METHODS
  Samples were collected from 22 CVVHDF circuits using citrate anticoagulation solutions (Prismocitrate 10/2 and Prism0cal) and from 26 circuits using Hemosol B0 and heparin anticoagulation. CVVHDF prescription, magnesium supplementation and anticoagulation choice was by the treating intensivist. We analysed 334 sample sets consisting of arterial, prefilter and postfilter blood and effluent. Magnesium loss was calculated from an equation for conservation of mass, and arterial magnesium concentration was described by an equation for exponential decay.
  
  
  RESULTS
  Using flow rates typical of adults receiving CVVHDF, we determined a median half-life for arterial magnesium concentration to decay to a new steady state of 4.73 hours (interquartile range [IQR], 3.73-7.32 hours). Median arterial magnesium concentration was 0.88mmol/L (IQR, 0.83-0.97mmol/L) in the heparin group and 0.79mmol/L (IQR, 0.69-0.91mmol/L) in the citrate group. Arterial magnesium concentrations fell below the reference range regularly in the citrate group and, when low, there was magnesium flux from dialysate to patient. Magnesium loss was greater in patients receiving citrate.
  
  
  CONCLUSIONS
  Exponential decline in magnesium concentrations was sufficiently rapid that subtherapeutic serum magnesium concentrations may occur well before detection when once-daily sampling was used. Measurements should be interpreted with regard to timing of magnesium infusions. We suggest that continuous renal replacement therapy fluids with higher magnesium concentrations be introduced in the critical care setting.
authors.affiliation: Launceston General Hospital, Launceston, TAS, Australia. matthew.brain@monash.edu
authors.forename: Matthew
authors.initials: M
authors.lastname: Brain
authors.forename: Mike
authors.initials: M
authors.lastname: Anderson
authors.forename: Scott
authors.initials: S
authors.lastname: Parkes
authors.forename: Peter
authors.initials: P
authors.lastname: Fowler
mesh_terms: D000328:Adult; D000368:Aged; D000925:Anticoagulants / Q000008:administration & dosage / Q000009:adverse effects*; D019540:Area Under Curve; D019343:Citric Acid / Q000008:administration & dosage / Q000009:adverse effects; D015314:Dialysis Solutions / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics; D005260:Female; D006207:Half-Life; D017583:Hemodiafiltration / Q000009:adverse effects* / Q000379:methods; D006493:Heparin / Q000008:administration & dosage / Q000009:adverse effects; D006801:Humans; D007262:Infusions, Intravenous; D008274:Magnesium / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D008275:Magnesium Deficiency / Q000097:blood / Q000139:chemically induced / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged
chemical_list: D000925:Anticoagulants; D015314:Dialysis Solutions; D019343:Citric Acid; D006493:Heparin; D008274:Magnesium