The use of heart-lung bypass machine or Cardiopulmonary Bypass (CPB) during cardiac surgery occassionally can cause some damage to major organs. In particular some patients sustain renal function impairment after CPB and this leads to a prolonged Intensive Care Unit stay, overall hospital stay, increased risk of death and eventually increases the cost of care. Other factors that contribute to a poor outcome in these patients postoperatively are advanced age, existing heart failure, duration of Cardiopulmonary Bypass and the length of the period by which blood is diverted away from the heart. It is estimated that up to 20% of patients undergoing cardiac surgery already have a pre-existing renal insufficiency and an increasing body of evidence suggests that a “whole body inflammation-like syndrome” occurs in patients with associated renal disease. For patients with suspected of having impaired kidney function after cardiac surgery, haemofiltration is usually applied in intensive care unit and high-dependence units which is costly and blocks beds. However, another form of haemofiltration has been devised recently that can be done on the patients at the same the patient is on bypass during the operation to remove excessive fluids and toxic materials in order to minimise the impact on kidneys that are already at risk damage. This form of haemofiltration is defined as “intraoperative haemofiltration”. However, it is still unknown whether intraoperative haemofiltration can remove some of the toxic by-products of metabolism that induce the inflammation-like syndrome to a level that will minimise postoperative complications. We wish to investigate the benefits of intraoperative haemofiltration when applied during cardiopulmonary bypass in terms of impact on length of intensive care unit stay, hospital stay and other secondary outcomes in high risk patients with preoperative renal impairment. The project outlined in this application will be the first to assess systematically the relative merits of intraoperative haemofiltration on a variety of factors such as length of stay in ITU, hospital stay, requirement for postoperative renal support, changes in biochemical markers of inflammation and oxidative stress in blood, changes in renal function and healthcare costs. It is anticipated that the project will take up to 3 years to demonstrate any impact. We fear that if the status quo remains, most of the patients that develop renal impairment before and during CPB operation would continue to be at increased risk of complications and death. The study will be the first to explore scientifically the merits of intraoperative haemofiltration and therefore will be hugely important in establishing treatment guidelines. Theatre study consumables £21,800 Laboratory consumables £15,624 Project management costs over 36 months £64,420 Total Costs £101,824