In more ways than one, Samer Nashef is a consultant at the cutting edge of his profession. As a cardiothoracic surgeon at Papworth hospital in Cambridgeshire, he has performed 409 coronary artery bypass grafts over the past three years. With just three deaths against his name, he has a survival rate of 99.27%.

But his international reputation extends beyond surgery to pioneering work on statistics that he believes may save patients' lives. In the late 1990s he led an international study group that developed the EuroSCORE system for predicting the outcome of heart surgery by analysing the risk factors presented by individual patients.

Surgeons feel especially accountable for poor results - even if they might be caused by other members of the operating team. "If a patient dies there is a clear causal and temporal relationship between the operation and the death. It's hard to escape," Mr Samer said.

"When a physician's patient dies, people say the patient didn't respond to treatment. In the case of a surgeon, they say the operation killed the patient."

For Mr Nashef and colleagues at Papworth, the EuroSCORE has become an important safety tool. Before picking up the knife to open up a patient's heart, they calculate the risks for each particular patient in an operation carried out by a particular surgeon.

Mr Nashef said the Papworth team has operated on patients whose chances of survival were less than 50% and, in some cases, as low as 7%. Many of them survived. Without the operation, they did not have long to live.

The pre-scoring technique provides the surgeons with an immediate check on whether their performance is above or below par. "If you can't tell whether your outcomes are up to scratch, you have no business doing heart surgery," Mr Nashef said. "You must know what you want to do and whether you achieve it. Otherwise you should not be treating people."

He said at least half the cardiac units in Britain do calculate risks before the operation begins. It was "shocking" that many still did not. Retrospective assessment made data much less reliable, he said. "If risks are not calculated in advance, figures can be plucked out of the air."

Mr Nashef said decisions on whether to operate on a high-risk patent were not as scary as they might seem to a layman. If the risks were presented simply and accurately, the patient could make an informed choice about whether to go ahead with the operation.

"They decide. It is their heart. It is their life," he said. "For me it is not that scary. I treat it as a service.

"At Papworth we have learned to cope with adverse events. They keep us awake at nights less. Any death is a catastrophe, but it can be set against the thousands of successful outcomes."

Mr Nashef's system of making judgments of risk based strictly on scores is controversial within the profession. Other eminent consultants believe prediction of risk involves art as well as science.

They seek to factor in less measurable variables such as the demeanour and robustness of the patient. But many surgeons believe that risk should be estimated and communicated to the patient.

Mr Nashef goes further. If the patient does not know his risk of death, he cannot give fully informed consent to the operation, he believes.