Sodium Bicarbonate in Cardiac Surgery

Many patients develop kidney failure after cardiac surgery. Although this kidney failure can usually be treated effectively, a longer stay in intensive care is often required. While many patients suffer no long term ill effects after developing post-operative kidney failure, some require long term kidney dialysis. We also know that patients who develop post-operative kidney failure are much more likely to die before they leave hospital. Why some people develop kidney failure after cardiac surgery is not known. However, doctors suspect that the process of cardiopulmonary bypass (where the functions of the heart and lungs are taken over by a machine during the operation, to allow the surgeon to operate) overactivates some of the same mechanisms the body uses to defend itself against severe infection. Many of the cell changes by which severe infection causes kidney failure also occur after cardiopulmonary bypass. One of the main overactive defence mechanisms is the release of highly toxic compounds derived from oxygen - a process called 'oxidative stress'. The investigators believe that sodium bicarbonate might reduce the oxidative stress, which occurs during cardiac surgery, and so prevent or decrease the kidney failure, which occurs in many patients. The investigators hope to give sodium bicarbonate (in similar doses to those used safely for treatment of acidosis) to patients during, and for 24 hours after cardiac surgery, and to compare the effects with patients who have not had sodium bicarbonate. The drug, or a placebo, will be given through the drip, which is present in all cardiac surgery patients. Whether a particular patient receives the drug or placebo will be decided at random, and neither the patient nor the investigators will know which has been given. We will measure kidney function before and after the operation using the standard blood tests. The investigators will also take four 20ml samples of blood, spaced before, during, and after the operation