title: The gap between calculated and actual calcium substitution during citrate anticoagulation in an immobilised patient on renal replacement therapy reflects the extent of bone loss - a case report.
abstract: BACKGROUND
  Demineralisation and bone density loss during immobilisation are known phenomena. However information concerning the extent of calcium loss during immobilisation remains inconsistent within literature. This may explain why treatment of bone loss and prevention of further demineralisation is often initiated only when spontaneous bone fracture occurred.Continuous renal replacement therapy is commonly utilised in critically ill patients with acute kidney injury requiring RRT. Regional anticoagulation with citrate for CRRT is well-established within the intensive care setting. Due to calcium free dialysate, calcium is eliminated directly as well as indirectly via citrate binding necessitating calcium substitution. In anuric patients declining calcium requirements over time reflect bone calcium liberation secondary to immobilisation. The difference between the expected and actual need for calcium infusion corresponds to calcium release from bone which is particularly impressive in patients exposed to long-term immobilisation and CRRT. We report a dialysis period in excess of 250 days with continuous renal replacement therapy and anticoagulation with citrate.
  
  
  METHODS
  We present a 30-year old male with prolonged multisystem organ failure after bilateral lung transplantation, in whom during a period of 254 days the cumulative difference between expected and actual need for calcium infusion was 14.25 mol, representing an estimated calcium loss of about 571 g. Comparison of computed tomographic imaging of the lower thoracic vertebrae over this period depicts a radiographically discernible decrease in bone density from 238 to 52 Hounsfield Units. The first spontaneous fracture occurred after 6 months of immobilisation. Despite subsequent treatment with bisphosphonates and androgen therapy resulting in an increase in bone density to 90 HU a further fracture occurred.
  
  
  CONCLUSIONS
  In immobilised patients receiving CRRT and anticoagulation with citrate, decreasing need for calcium substitution reflects the degree of bone demineralisation corresponding with radiographic assessment of declining bone mineral density. Such a declining need for calcium substitution could be useful in clinical practice highlighting relevant bone loss which results in spontaneous fractures in immobilised critically ill patients.
authors.affiliation: Department of Internal Medicine, Nephrology and Hypertension, Saarland University Medical Centre, Homburg-Saar, Germany. matthias.klingele@uks.eu.
authors.forename: Matthias
authors.initials: M
authors.lastname: Klingele
authors.forename: Sarah
authors.initials: S
authors.lastname: Seiler
authors.forename: Aaron
authors.initials: A
authors.lastname: Poppleton
authors.forename: Philip
authors.initials: P
authors.lastname: Lepper
authors.forename: Danilo
authors.initials: D
authors.lastname: Fliser
authors.forename: Roland
authors.initials: R
authors.lastname: Seidel
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000627:therapeutic use; D001510:Bed Rest / Q000009:adverse effects*; D050071:Bone Density Conservation Agents / Q000627:therapeutic use; D002118:Calcium / Q000008:administration & dosage / Q000097:blood / Q000627:therapeutic use*; D012080:Chronic Kidney Disease-Mineral and Bone Disorder / Q000097:blood / Q000188:drug therapy* / Q000209:etiology; D002951:Citrates / Q000627:therapeutic use; D003550:Cystic Fibrosis / Q000601:surgery; D004164:Diphosphonates / Q000627:therapeutic use; D018450:Disease Progression; D004305:Dose-Response Relationship, Drug; D017809:Fatal Outcome; D005598:Fractures, Spontaneous / Q000209:etiology; D006440:Hemofiltration / Q000009:adverse effects*; D006801:Humans; D016040:Lung Transplantation; D008297:Male; D009102:Multiple Organ Failure / Q000209:etiology; D010281:Parathyroid Hormone / Q000097:blood; D011183:Postoperative Complications / Q000097:blood / Q000188:drug therapy* / Q000628:therapy; D012086:Reoperation; D013739:Testosterone / Q000627:therapeutic use; D014807:Vitamin D / Q000097:blood
chemical_list: D000925:Anticoagulants; D050071:Bone Density Conservation Agents; D002951:Citrates; D004164:Diphosphonates; D010281:Parathyroid Hormone; D014807:Vitamin D; D013739:Testosterone; D002118:Calcium