Rationale:

A higher citrate dose during continuous venovenous hemofiltration provides better anticoagulation but possibly a higher risk of citrate accumulation in case of metabolic limitations. A higher citrate dose also increases magnesium loss in ultrafiltrate, while a negative magnesium balance is unwanted.

Objective:

Aim of this study is to determine the magnesium balance of citrate-based continuous veno-venous hemofiltration (CVVH) and to determine whether and to which extent the magnesium balance depends on citrate dose.

Study design and methods:

A prospective randomized study conducted in critically ill patients with acute kidney injury (AKI), treated with CVVH, with either low dose citrate (2.5 mmol/L blood flow in the filter) or high dose citrate (4.5 mmol/L blood flow in the filter) as anti-coagulant, targeting a postfilter ionized Calcium (iCa) of resp. 1.3-1.6 mg/dL (0.325-0.4 mmol/L) and 0.8-1.1 mg/dL (0.2-0.275 mmol/L). Post-filter blood as well as effluent aliquots and bloodconcentrations in the patient are tested for the following variables:

(0 , 2 , 4, 6, 12 and 24 hrs): Total Magnesium (tMg) and total Calcium (tCa), ionized Ca (iCa)(bloodgas analyzer). In addition, hematocrit, albumin, total protein, ureum and creatinine and parathormone (PTH) are determined in arterial blood at 0 and 24 hrs or at the time of protocol exit and citrate concentrations in postfilter and arterial blood at 1 and 24 hrs or at protocol exit.

Sample sites: arterial line, postfilter port (after postdilution and calcium compensation), effluent sample. All flow rates to be noted.

Study population:

Twenty patients admitted to intensive care, requiring continuous renal replacement therapy (CRRT) for AKI.

Intervention:

Anti-coagulation with either low dose citraat (2.5 mmol/L blood flow) or high dose citraat (4.5 mmol/L blood flow) targeting postfilter iCa of resp. 1.3-1.6 and 0.8-1.1 mg/dL. Both regimens are within standard protocolled CVVH treatment in the intensive care department.

Inclusion Criteria:

• Critically ill patients requiring CRRT for AKI (RIFLE criteria)
• Written informed consent from the patient or legal representative

Exclusion Criteria:

• pre-existing chronic renal insufficiency requiring dialysis
• chronic immunosuppression
• liver cirrhosis Child-Pugh C
• severe or shock-related hepatitis
• Pregnancy