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, from the arterial catheter routinely inserted in every patient. This blood would be used to measure oxidative stress, and also some of the proteins inside the blood cells, which are responsible for creating the toxic oxygen compounds. In this way we will discover not only the effect of sodium bicarbonate, but also the mechanism of that effect.

Sodium bicarbonate is commonly used to treat metabolic acidosis in severe renal disease, circulatory insufficiency due to shock or severe dehydration and has been shown to be an effective drug in preventing contrast-induced nephropathy.

Sodium bicarbonate is considered to be safe in the setting of intensive care treatment and is often used in the treatment of patients with metabolic acidosis without any discernible adverse clinical effects.

This is a pilot study. If the drug proves effective in this context, further studies on a larger scale would be required to justify its general use.

There will be no extra risk to a patient who participates in the study, and no discomfort other than that normally associated with cardiac surgery.

Informed consent will be obtained from the patient prior to the operation by one of the investigators or the ICU research nurse. The clinical care of a patient who does not consent for any reason will not be affected.