The PuO2 in RenalGuard (PURE) study is planned as a single center, randomized controlled pilot study comparing renal oxygenation during cardiac surgery with cardiopulmonary bypass (CPB) with or without balanced forced diuresis using the RenalGuard (RG) system.

Renal oxygenation will be assessed by urine oxygen tension, continuously measured by optodes placed through the urine catheter. Measurements will start after induction of anesthesia and continue for 24 hours.

In total, 30 patients will be randomized 1:1 to RG or standard of care (SOC) during cardiac surgery with CPB. In the RG group, the forced diuresis with neutral fluid balance will be maintained from before the start of surgery until 3 hours after weaning from CPB.

The primary endpoint is the group difference (RG vs SOC) in delta PuO2, defined as the change in mean PuO2 from baseline to the last 5-minute period at 45 minutes after start of CPB.

The secondary endpoints include

1. Group difference in mean PuO2 before, during and after CPB
2. Group difference in time weighted area under the curve for PuO2
3. Group differences in renal near infrared spectroscopy (NIRS) before, during and after CPB
4. Group difference in urine and blood biochemistry including renal biomarkers
5. Group difference in urine output and fluid balance during surgery and first postoperative day
6. Group differences in postoperative AKI according to the KDIGO criteria
7. Time (minutes) with puO2 ≤ 15 and ≤ 10 mmHg during and after CPB
8. Dynamics of PuO2 during the early postoperative phase

Patients ≥18 years scheduled for cardiac surgery with CPB with estimated glomerular filtration rate ≥50 ml/min are eligible for inclusion. Exclusion criteria include patients on higher doses of furosemide, patients with AKI or under renal replacement therapy.

Patients will be analyzed according to study group. In patients where hemofiltration has been used during CPB, control group patients who has received furosemide and patients in the RG group who do not reach target urine flow will be excluded from the main analysis but will be included in a separate analysis.

Inclusion Criteria:

• Patients ≥18 years of age
• scheduled for cardiac surgery with normothermic CPB
• Estimated glomerular filtration rate ≥50 ml/min as assessed by the CKD-EPI formula

Exclusion Criteria:

• Patient receiving furosemide at a dose>100 mg/day orally (or the equivalent dose of an alternative loop diuretic) in the last week
• Patient who cannot be urethrally catheterized for any reason
• Patient already dialysis dependent
• Known or suspected AKI (KDIGO criteria) at the time of screening
• Any condition which, in the judgement of the investigator, might increase the risk to the patient

Parts of the data may be analyzed in other projects