Acute kidney injury is a potentially life threatening condition which affects 1 in 2 patients in the Intensive Care Unit (ICU). Patients often need dialysis treatment, also called renal replacement therapy. Renal replacement therapy is a treatment that removes toxins and excess fluid from the blood stream. It consists of having a small plastic catheter in a vein in the neck or in the groin through which blood flows through a dialysis machine and is cleansed and excess water is removed. The cleansed blood is then returned to the patient via the same catheter.

One of the major areas of uncertainty for doctors in the ICU is "What is the right intensity of renal replacement therapy for patients with acute kidney injury?" A higher intensity indeed removes more toxins but also removes other substances in the blood, including vitamins, nutrients and important medications. The current usual dose is around 25 ml/kg/hr but clinical practice in the UK is very variable and some patients routinely receive higher doses and some get lower doses. Data from large databases worldwide have suggested that a lower dose is safe and effective and may potentially allow the kidneys to recover faster but confirmation is lacking.

In this study, the investigators investigate whether renal replacement therapy at a lower intensity is as effective and safe as currently used doses. Participants will be randomised to receiving renal replacement therapy at usual or lower intensity. There will be no change to any other aspects of treatment.

The results will inform the investigators whether the study protocol is feasible and how best to design a future larger research study.

Acute kidney injury is a potentially life threatening condition which affects 1 in 2 patients in the Intensive Care Unit (ICU). Patients often need dialysis treatment, also called renal replacement therapy. Renal replacement therapy is a treatment that removes toxins and excess fluid from the blood stream. It consists of having a small plastic catheter in a vein in the neck or in the groin through which blood flows through a dialysis machine and is cleansed and excess water is removed. The cleansed blood is then returned to the patient via the same catheter.

One of the major areas of uncertainty for doctors in the ICU is "What is the right intensity of renal replacement therapy for patients with acute kidney injury?" A higher intensity indeed removes more toxins but also removes other substances in the blood, including vitamins, nutrients and important medications. The current usual dose is around 25 ml/kg/hr but clinical practice in the UK is very variable and some patients routinely receive higher doses and some get lower doses. Data from large databases worldwide have suggested that a lower dose is safe and effective and may potentially allow the kidneys to recover faster but confirmation is lacking.

In this study, the investigators investigate whether renal replacement therapy at a lower intensity is as effective and safe as currently used doses. Participants will be randomised to receiving renal replacement therapy at usual or lower intensity. There will be no change to any other aspects of treatment.

The investigators aim to recruit 20 patients in the UK. Fully anonymised results will be shared with researchers in Canada who are conducting the same study.

Inclusion Criteria:

• age ≥ 18 years
• patient weight ≥ 55 kg
• plan to start CRRT or within 24 hours of having started CRRT for AKI
• expected to survive and receive CRRT for a duration of ≥ 48 hours

Exclusion Criteria:

• indication for sustained higher dose-intensity CRRT
• end-stage kidney disease receiving maintenance dialysis
• previous receipt of RRT for AKI during the current hospitalization
• inability to comply with the requirements of the study protocol