The assessment of renal functional reserve (RFR) has been proposed for the risk stratification of patients undergoing potentially nephrotoxic procedures. The present pilot study is designed to explore the correlation between IRRIV and RFR under pathologic conditions.

Renal functional reserve (RFR) represents the capacity of the kidney to increase glomerular filtration rate (GFR) in response to certain physiological or pathological stimuli or conditions.

RFR is calculated as the difference between the measured maximum GFR achieved through a renal stress test and the baseline GFR measured in rest conditions. In clinical practice, the most common renal stress test is performed as a standardized protein loading test. Recently, in a pilot study, the investigators demonstrated a significant correlation between RFR and the intra-parenchymal renal resistive index variation (IRRIV) during an echo renal stress test in a cohort of healthy volunteers. IRRIV test has proven to be rapid, safe, bedside and easy to perform and it might represent a preliminary test in screening patients' RFR.The present pilot study is designed to explore the correlation between IRRIV and RFR under pathologic conditions.

Inclusion Criteria:

• Estimated GFR (CKD-EPI) greater than or equal to 60 mL/min/1.73 m2
• Scheduled cardiac surgery with cardiopulmonary bypass (coronary artery bypass, valve replacements, combined or other operations).

Exclusion Criteria:

• Age less than 18 years old
• Pregnancy
• Ultrasound evidence of morphological kidney abnormalities and/or renal artery stenosis
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Contrast media in the 2 days before the tests.

Patients scheduled for cardiac surgery with cardiopulmonary bypass (coronary artery bypass, valve replacements, combined or other operations)