MiECS is one of the largest multicentre randomised controlled trials on extracorporeal circulation conducted under the auspices of Minimal Invasive Extracorporeal Technologies International Society (MiECTiS). It is designed to ultimately address the emerging effectiveness of MiECC systems in the light of modern perfusion practice worldwide. The primary hypothesis is that MiECC, as compared to conventional CPB (cCPB), reduces the proportion of patients experiencing serious perfusion-related postoperative morbidity after cardiac surgery. The study will be led by the Clinical Research Unit of the Special Unit for Biomedical Research and Education (SUBRE), Aristotle University of Thessaloniki School of Medicine in Greece (AUSoM) with Chief Investigator Professor Kyriakos Anastasiadis, who is a key-opinion-leader in the field of MiECC, founder and Executive Board of MiECTiS.

Despite a fall in mortality rates over the past decade, patients having cardiac surgery continue to experience serious postoperative complications. The risk of serious and relatively common surgical complications is often a consequence of stopping the heart during the operation, using the heart and lung machine (conventional cardiopulmonary bypass; cCPB), and restarting and reperfusing the heart at the end of the operation. Although several strategies have been developed to reduce such complications, they still occur and can be life threatening; they also increase the length of time a patient spends in the hospital.

Miniaturised heart lung machines (minimally invasive extracorporeal circulation; MiECC) have been developed with the aim of reducing the number of postoperative complications arising from using cCPB. Because of the variety of miniaturised systems that have been evaluated, the different types of patients and outcomes investigated, and the poor quality of previous studies, the effectiveness of MiECC in reducing postoperative complications has not been established and most hospitals continue to use cCPB.

Our primary hypothesis is that, compared to cCPB, using a MiECC system during cardiac surgery reduces the proportion of patients having one of several serious postoperative complications (death, myocardial infarction, stroke, acute kidney injury, reintubation, tracheostomy, mechanical ventilation for more than 48 hours, or reoperation) up to 30 days after surgery. In addition, the investigators hypothesise that MiECC reduces the amount of blood products transfused, time to discharge from the cardiac intensive care unit and hospital and the health care resources used during the hospital stay.

Study investigators propose to carry out a large, multicentre randomised controlled trial in 10 to 15 cardiac surgery centres worldwide. Patients will be eligible if they are having coronary artery bypass surgery, aortic valve replace or both using a heart lung machine without circulatory arrest. Centres may recruit patients having all, or a subset of, operation types.

It is expected that 20 % to 23% of patients will experience one or more of the serious complications (the primary outcome). In order to be able confidently to detect a 30% relative reduction in the risk of this outcome, the investigators plan to recruit 1,300 participants across all sites.

Inclusion Criteria:

• All patients undergoing any elective or urgent coronary artery bypass grafting (CABG), aortic valve replacement (AVR) or CABG+AVR surgery using extracorporeal circulation without circulatory arrest.

Exclusion Criteria:

• Requirement for emergency or salvage operation.
• Requirement for major aortic surgery (e.g. aortic root replacement).
• Contraindication or objection (e.g. Jehovah's Witnesses) to transfusion of blood products.
• Congenital or acquired platelet, red cell or clotting disorders (patients with iron deficient anaemia will not be excluded).
• Inability to give informed consent for the study (e.g. learning or language difficulties).