<h3>Objective</h3> Cardiac surgery involving cardiopulmonary bypass carries a high risk for development of acute kidney injury (AKI). It is difficult to investigate a specific causal relationship to AKI with in vivo studies due to the multifactorial etiology and the fact that rapid changes in kidney physiology often requires high-sensitivity invasive measurements. Most proof-of-concept studies are performed in rodent models, where renal physiology has distinct differences compared to humans. Larger mammals, such as pigs, have a closer resemblance of the human immune system and anatomy. In this respect, we have developed an experimental ex vivo animal model using porcine kidneys to evaluate potential renoprotective medical treatments assessed under standardized hemodynamic conditions (blood pressure/flow- and oxygen supply) with close resemblance to cardiopulmonary bypass. <h3>Design and method</h3> Kidney retrieval Pigs of approximately 40 kg are used for the model. Following general anaesthesia, a midline laparotomy is performed for localisation of the aorta, vena cava and both kidneys. A sheet is placed in the abdominal aorta and 600 mL of whole blood is collected in sterile blood bags containing citrate phosphate dextrose. Both kidneys are located and vascular clamps placed on the renal artery and vena cava (above and below the renal veins) followed by ligatures. An overdose of pentobarbital is administered for euthanasia, and the kidney with viable parts is retrieved. Next, the renal artery and vein are cannulated using a LifePort® straight cannula (Organ Recovery Systems), and the ureter is cannulated using a 10 Fr nasogastric tube. The kidney is flushed with 100 mL sodium chloride mixed with 5.000 IE Heparin. Ex vivo machine perfusion: The perfusion circuit consist of 1/4" and 3/8" PVC tubes, a hard-shell reservoir (VHK 11000, Maquet), a magnetic pump head connected to a centrifugal pump unit (RF-32, Maquet), and an oxygenator (Quadrox-I Neonatal, Maquet). The temperature within the oxygenator is kept at 37˚C using a water supply heater unit (HU 35, Maquet). A gasmixer (20090, Sechrist) is used to maintain a PaO2 above 100 mmHg and a PaCO2 at approximately 40 mmHg. Perfusion pressure is measured as a side-pressure on the LifePort® arterial cannula using an invasive pressure module (M1006B, Phillips). Blood flow is monitored using an ultrasonic flow probe and rounds per minute is set to maintain a blood flow of 300 mL per min. The perfusion system is primed with a combination of autologous whole blood and Ringer's acetate solution with 5.000 IE heparin. Plasma and urine levels of porcine NGAL is commercially available (Kit 044, BioPorto Diagnostics). We have developed specific porcine NGAL mRNA primers for qPCR analysis. Histological tissue samples from the renal cortex are HE-stained and evaluated by a pathologist using an injury score. <h3>Conclusions</h3> We have developed an experimental ex vivo animal model using porcine kidneys in order to study the pathophysiology of cardiopulmonary bypass-associated AKI. We believe that potential renoprotective interventions can be better evaluated in a model providing standardised conditions for observation.