The purpose of this study is to evaluate the possible association between portal vein flow pulsatility and acute kidney injury after cardiac surgery. Participants will undergo assessment of portal vein flow and intra-renal blood flow using bedside Doppler ultrasound before surgery and daily for three days after cardiac surgery.

Acute kidney injury is a frequent complication after cardiac surgery. Venous congestion from right ventricular dysfunction and fluid overload can impair kidney perfusion resulting in the cardio-renal syndrome.

An increase in the variation of blood flow velocity in the portal vein during the cardiac cycle called portal pulsatility is a sign of congestive heart failure. Portal pulsatility occurs when increased central venous pressure results liver venous congestion. The presence of abnormal portal pulsatility could be used as a marker of venous congestions in other organs such as the kidneys. Discontinuous intra-renal vein flow is a risk factor for death or re-hospitalization in heart failure patients and could be seen in patients with portal pulsatility.

Inclusion Criteria:

• 18 years and older.
• Undergoing cardiac surgery with the use of cardiopulmonary bypass
• Able to provide consent.

Exclusion Criteria:

• Chronic renal replacement therapy before the procedure.
• Chronic kidney disease stage 5 defined as a estimated glomerular filtration rate by the MDRD equation (eGFR-MDRD) of 15 mL/min/1,73m2 or less.
• Critical pre-operative state defined as aborted sudden death, preoperative cardiac massage, preoperative ventilation before anaesthetic room, preoperative inotropes or intra-aortic counterpulsation balloon.
• Patients previously diagnosed with a condition interfering with Doppler evaluation of the portal system: Portal vein thrombosis, Cirrhosis.
• Patients with documented AKI before surgery.
• Confirmed or suspected pregnancy.
• Kidney transplant recipients.

Patients undergoing elective or urgent cardiac surgery with the use of cardiopulmonary bypass.