Hemodynamic Effects of Blood Flow Variation in Continuous Renal Replacement Therapy

Inclusion Criteria: * Age 18-89 * Acute renal failure or end-stage renal disease necessitating CRRT * Admitted to the MICU service * If on vasopressor/inotropic agent, norepinephrine as only intravenous pressor * If on vasopressor/inotropic agent, at stable pressor dose for at least four hours * If on IV fluids, stable dose of crystalloids \<= 100cc/hour and is not receiving colloids for 4 hours or more prior to initiation of CRRT * Mean arterial pressure (MAP) \>= 65 * Arterial catheter present for continuous blood pressure monitoring * CRRT duration of 48 hours or less using NxStage System One dialysis system * successfully tolerated CRRT for at least 4 hours without clotting or hemodynamic instability * no other procedures, blood products transfusion, or additional medication administration are anticipated during the study period Exclusion Criteria: * listed for organ transplant * atrial fibrillation, other irregular heart rhythm, unstable arrhythmia * need for more than one intravenous vasopressor agent * intravenous vasopressor/inotropic agent other than norepinephrine (ie dobutamine, dopamine, vasopressin, epinephrine) * therapeutic anticoagulation being administered * known acute myocardial infarction as defined by elevated troponin along with a documented clinical diagnosis during current hospitalization * known acute stroke, intracerebral hemorrhage, intracranial mass effect, or elevated intracranial pressure within the last 30 days. * dialysis catheter malfunction and unable to maintain target blood flow rate * fluid removal (ultrafiltration) rate \> 100mL/hour