The aim of the study are: 1) To evaluate the occurrence of acid-base alterations and the incidence of hypophosphatemia during different modalities of Renal Replacement Terapy (RRT) in critically ill patients [CVVH, CVVHDF and SLED (Sustained Low-Efficiency Dialysis)] by using a simplified Regional Citrate Anticoagulation (RCA) protocol combined with the adoption of a phosphate-containing solution as dialysate and/or replacement fluid; 2) To optimize the infusion rates of different solutions adopted, including citrate, in order to obtain an appropriate electrolyte and buffer supply. The final aim of this approach will be to reduce the need for frequent monitoring of acid-base status and electrolytes (with special regard to ionized calcium levels), and to avoid the need for frequent adjustments of RCA-RRT parameters (infusion rate of different solutions, electrolytes supplementation in the course of RRT). This approach could allow to simplify anticoagulation protocols with citrate, in order to minimize potential concerns hampering a wider diffusion of RCA in daily practice.

The need for continuous anticoagulation represents a potential drawback of RRT modalities. KDIGO 2012 guidelines on acute kidney injury (AKI) suggest the adoption of RCA as first choice anticoagulation modality for continuous RRT (CRRT) in patients without contraindications for citrate. Citrate has been also introduced as anticoagulant for SLED and its use in the context of a mainly diffusive prolonged intermittent modality has been shown to represent an easy and safe method to maintain the extracorporeal circuit when concentrated citrate solutions, such as ACD-A are used. Hypophosphatemia is a known issue of RRT, and has been reported in up to 50-80% of cases when standard RRT solutions are used, especially in continuous/prolonged intermitted modalities when high RRT doses are delivered. RRT-related phosphate depletion should be avoided in critically ill patients due to the relevant hypophosphatemia-associated complications in this clinical setting. The adoption of phosphate-containing CRRT solutions could reduce the incidence of hypophosphatemia and minimize the need for parenteral phosphorus supplementation.The adoption of a commercially available phosphate-containing CRRT solution, in the setting of RCA-RRT may allow to meet the double target of minimizing RRT-induced hypophosphatemia and ensuring an adequate circuit life, also avoiding electrolyte and acid-base derangements.

Inclusion Criteria:

• age >= 18 years
• critically ill patients requiring continuous or prolonged intermittent renal replacement therapy for severe acute kidney injury (AKI)
• critically ill patients requiring continuous or prolonged intermittent renal replacement therapy for end stage renal disease (ESRD)

Exclusion Criteria:

• age < 18 years

Critically ill patients aged >=18 years with severe acute kidney injury (AKI) or end stage renal disease (ESRD) requiring renal replacement therapy