To investigate the influence of preoperative fluid and food intake in cardiac surgery patients on the development of postoperative AKI.

Acute renal failure (ARF) and the need for renal replacement therapy (RRT) is a major complication after cardiac surgery, associated with mortality and an increased risk to develop end-stage renal disease. Cardiac surgery patients are at increased risk to develop acute kidney failure due to ischaemia-reperfusion injury, cardiopulmonary bypass (CPB) induced inflammation and haemolysis, hemodynamic alterations, vasoconstriction and resulting reduced renal perfusion. According to the current literature, AKI occurs in average in 20-30% after cardiac surgery with an incidence of RRT in 1-5%. Several reviews revealed the literature and concluded that , inter alia, euvolemia, adequate nutrition, the avoidance of nephrotoxic drugs and anemia optimization belong to the most effective prevention strategies.

Patients are instructed to follow the nil per os (NPO) guidelines, including abstinence of clear liquids for >2 hours preoperative as well as fasting time of light foods for > 6 hours and fatty foods for >8 hours prior to surgery. However, these guidelines encourage patients to continue PO hydration until 2 h before surgery in order to optimize the volume status. Besides the fact that NPO lasts in average critically longer than required, surgery delay is a common issue and may lead to an exceedance of NPO up to twice as long as required.

Data about the exact mechanism is still sparse, but preoperative iv hydration may correct or even expand intravascular volume, improve renal perfusion and induce diuresis, stimulate endogenous natriuretic peptides release and inactivate the renin-angiotensin-aldosterone system (RAAS).

Large trials on this very relevant topic in these high risk cardiac surgery patients are absolutely missing. Therefore, this prospective observational study aims to investigate the influence of varied preoperative fluid and food intake in cardiac surgery patients on the development of postoperative AKI.

Inclusion Criteria:

• Adult patients (>18 years of age) scheduled to undergo elective cardiac surgery with the use of cardiopulmonary bypass (CPB) and cardioplegic arrest

Exclusion Criteria:

• Patients not willing to participate or not able to give informed consent
• Patients receiving contrast agents within 72 hours before surgery
• Patients with preoperative need for renal replacement therapy
• Patients receiving an extracorporeal mechanical assist device (e.g. ECLS) or for advanced heart failure therapies (e.g. TAH, VAD) will be excluded.
• Patients participating in another interventional trial
• Pregnant or lactating patients

Patients undergoing elective cardiac surgery at the University Hospital RWTH Aachen