Patients in intensive care units with acute kidney injury are often too frail to undergo the rapid fluid shifts that accompany intermittent hemodialysis. Continuous renal replacement therapy (CRRT) allows a more gentle continual dialysis, more similar to regular kidney function. Anticoagulation of the CRRT circuit can reduce clotting of the filter, which can lead to less filter changes and possibly less transfusions. Niyad (nafamostat mesylate), an anticoagulant with an ultra-short half-life of 8 minutes, is approved for use in South Korea and Japan for anticoagulation of the CRRT circuit. For patients who cannot tolerate heparin or who are at a high risk of bleeding, nafamostat may be an optimal anticoagulant to infuse into the CRRT circuit as the short half-life should minimize patient exposure. The primary objective of this study is to measure the anticoagulation efficacy of Niyad in the CRRT circuit versus placebo. Evaluation of the safety of Niyad in patients undergoing CRRT versus placebo will also be performed.