Sepsis is responsible for 50% of all acute kidney injury (AKI) in intensive care units (ICUs), contributing greatly to multiple organ dysfunction syndrome (MODS). Special types of continuous renal replacement therapies (CRRT) have been proposed as adjuvant therapies for septic shock due to their ability to remove middle molecular weight molecules such as inflammatory mediators involved in MODS pathophysiology. These therapies are called extracorporeal " blood purification " therapies.

When CRRT is used, an anticoagulation is required to prevent clotting of the extracorporeal circuit, possibly causing bleeding in selected patients. Many anticoagulation strategies have been proposed and the most commonly used in 2013 is still unfractionated heparin. Regional citrate anticoagulation (RCA) is an interesting alternative as it dramatically decreases the bleeding risk.

The investigators hypothesize that the use of citrate with Super High Flux Continuous Veno-Venus Hemodialysis (SHF-CVVHD) would be highly beneficial over time by preserving the filter effectiveness via limiting protein adhesion (which subsequently reduces filter pore sizes (protein cake)), as compared to heparin. Consequently, higher clearances of the inflammatory mediators could be maintained over time with citrate as compared to heparin anticoagulation. In other words, for the same duration of filter use, middle molecular weight molecules and cytokines clearances would be greater with citrate as compared to heparin. To test this hypothesis, the investigators will perform a clinical randomized controlled trial which aim would be to compare middle molecular weight molecules and cytokines clearances in SHF-CVVHD using RCA versus systemic heparin anticoagulation in septic patients with AKI.

Inclusion Criteria:

• Male or female critically ill patients over the age of 18 years old
• Acute Kidney Injury requiring CRRT defined using the Risk, Injury, Failure, Loss, End-stage renal disease (RIFLE) classification with criterion I or worse.
• Septic shock as defined by the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference.
• Written informed consent obtained from the patient or a patient's legal representative
• Patient patient's legal representative able to agree to patient's enrollment in the study with informed consent.

Exclusion Criteria:

• Pregnancy
• Participation in another research study protocol
• Known heparin induced thrombopenia or contraindication to heparin
• Pre-existing chronic renal failure on chronic dialysis
• Therapeutic anticoagulation with heparin for another reason (e.g. chonic arrhythmia)
• Severe liver failure (15% prothrombin time)