The goal of this prospective observational study is to define a risk profile for cardiovascular surgery associated acute kidney injury (AKI), using clinical patient characteristics, operation parameters as well as blood and urine laboratory values.

The main question it aims to answer is:

• Does a combination of the factors mentioned above better predict patient outcome than classical factors used to date in clinical practice?

Participants of this study are adults aged 18 and above who are scheduled for elective heart or main artery surgery, and who have given written informed consent.

The difficulty of precisely predicting AKI following major surgery is a clinical challenge and unmet need as treatment should be introduced within 24-48 hours. In addition there is no available treatment to date apart from supportive therapy such as renal replacement therapy.

Therefore, early identification of patient-specific biomarkers and other clinical predictors could help to better understand the association with AKI and other patient outcomes. In addition to the "classical" risk factors (age, diabetes, pre-existing CKD), frailty might represent another important variable, as shown in previous observational studies. Importantly frailty is not unique to age, although it occurs in approximately 25% of those over 65 and affects more than half of the population aged 85 and older, as it has been shown to be highly prevalent in hospitalized patients and/or patients with CKD. Furthermore, in preclinical studies the serum protein Fetuin-A was identified as potential biomarker for vascular surgery associated AKI.

PEAK is a single center, prospective observational study involving several clinics at the University Hospital Bern. Besides from demographic data and perioperative parameters, blood and urine are collected with high granularity during and immediately after surgery (15min after the first cut, start and end of cardiopulmonary bypass (CBP) or aortic clamping (X-clamp), 4 hours after surgery) and at day 1, 2, 3, and 7 (or discharge) post-surgery. In addition renal function will be assessed at day 90. Furthermore, study participants will answer the Edmonton frailty questionnaire at baseline and at day 90.

Inclusion Criteria:

• Patients undergoing elective cardiovascular surgery, such as valvular replacement surgery, with or without combined coronary artery bypass graft (CABG), or thoracic or abdominal aortic surgery.
• Written informed consent obtained prior to surgery.

Exclusion Criteria:

• Patients with a kidney transplant or on renal replacement therapy
• Severe liver failure, defined by the presence of encephalopathy, Factor V < 50% and INR >1.5 on preoperative blood sample (within 4 weeks).

Patients undergoing elective cardiovascular surgery at the University Hospital Bern (Inselspital), Switzerland