Inclusion Criteria:  Receiving or plan to receive CRRT with the HF20™ filter as standard of care  Acute kidney injury (AKI) or fluid overload as defined as one of the two below:  AKI defined as Kidney Disease Improving Global Outcomes (KDIGO) Stage 1 or higher by either:  Serum creatinine criteria (0.3 mg/dL increase over baseline in 48 hours, or a 50 percent increase within the previous 7 days) or Urine output criteria (less than 0.5 mL/kg/hr for 6 or more hours) Severe fluid overload defined as greater than 10 percent fluid accumulation based on ICU admission weight  Exclusion Criteria:  Weight less than 8 kilograms Weight more than 20 kilograms Patient not expected to survive more than 48 hours Received renal replacement therapy in the previous 5 days