The goal of this clinical trial is to assess the effect of RenalGuard Therapy in reducing the rates of Acute Kidney Injury (AKI) within 72 hours after cardiac surgery in patients at risk of developing Cardiac Surgery Associated AKI (CSA-AKI) compared to standard-of-care (SoC).

Participants will be randomized (1:1) to one of the two study groups. The Treatment study group will be managed with the RenalGuard System. The RenalGuard treatment will start after induction of anesthesiology and will run during surgery and for 6-7 hours in the Intensive Care Unit (ICU). The treatment will aim to achieve a urine rate above a predefined urine rate threshold. Patients in the control group will be managed based on the usual clinical practice in cardiac surgery centres as detailed in the recommendations for CSA-AKI prevention by accepted clinical guidelines.

For both study groups general anaesthesia, cardiopulmonary bypass (CPB) run and overall patient care will be based on SoC for cardiac surgery.

Patients will be followed up for up to 7 days post surgery or until discharge, which ever comes first.

Long-term follow up will be performed at 90 days post surgery.

Inclusion Criteria:

1. Male or female and >18 years of age

2. Patient able to give written consent

3. Scheduled for the following non-emergent cardiac surgery procedure requiring CPB, isolated or in combination:

   • coronary artery bypass graft (CABG)
   • aortic valve replacement or repair alone, with or without aortic root repair
   • mitral, tricuspid, or pulmonic valve replacement or repair
   • simultaneous replacement of several cardiac valves
   • CABG with aortic, mitral, tricuspid, or pulmonic valve replacement or repair
   • Surgery on the aorta: aortic root and/ or ascending aorta
   • Atrial fibrillation (AF) ablation surgery if combined with other cardiac procedures.
   • Atrial septal defect (ASD) closure if combined with other cardiac procedures.
   • Excision of myxoma if combined with other cardiac procedures

4. Have at least one of the following risk factors for CSA-AKI:

   • CKD-EPI eGFR 20-59 mL/min/1.73 m²
   • Age ≥ 75 years
   • Undergoing combined surgery (e.g. CABG + Valve)
   • Logistic EuroScore of ≥5 or, Euroscore II of ≥4 or Society of Thoracic Surgeons (STS) Score ≥4
   • Left ventricular ejection fraction (LVEF) ≤ 35% by invasive or noninvasive diagnostic cardiac imaging performed within 90 days prior to surgery.
   • Insulin-requiring diabetes
   • Non-insulin-requiring diabetes with HbA1C ≥ 6.1% in the last 6 months
   • Preoperative anemia within 4 weeks of surgery

Exclusion Criteria:

1. Patient requiring emergency surgery
2. Surgery to be performed without CPB
3. Patient receiving furosemide at a dose>100 mg/day orally (or the equivalent dose of an alternative loop diuretic) in the last week
4. Patient who cannot be urethrally catheterize for any reason
5. Patients already dialysis dependent
6. Patients with CKD-EPI eGFR <20 mL/min/1.73 m²
7. Known or suspected AKI (KDIGO criteria) at the time of screening
8. Patients participating in another interventional drug or device study or have received an investigational drug or device treatment within the last 30 days
9. Pregnant patient, self-reported
10. Patients whose planned surgery to be performed under conditions of circulatory arrest or hypothermia with rectal temperature < 28°Celsius (82.4° Fahrenheit)
11. Patient with suspected or confirmed bacteraemia, endocarditis, or pyelonephritis at hospital admission
12. Patients with pneumonia, aspiration, or bilateral pulmonary infiltrates from an infectious aetiology reported on chest x-ray or CT scan in the last 7 days
13. Patients in cardiogenic shock or hemodynamic instability which require inotropes or vasopressors or other mechanical devices (Impella Heart Pump, IABP) within 24 hours prior to surgery
14. Patients on extracorporeal membrane oxygenation (ECMO) or durable ventricular assist device (VAD) at the time of screening, or planned use within 24h prior to surgery
15. Patients currently treated with chemotherapy or radiation therapy that may have an impact on kidney function.
16. Patient underwent prior solid organ transplantation
17. Patients underwent major surgery within the last 3 months
18. Any condition which, in the judgement of the investigator, might increase the risk to the patient.

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