By the time Dr Lee finishes another day of operations and ward rounds, he will have clocked up 34 hours on duty.

Hong Kong is notorious for its long working hours - but what most people consider a long day at the office pales in comparison with the exhausting hours kept by those responsible for healing the sick.

Working more than double the average person's working week has long been considered the norm for doctors, but mounting evidence is proving that not only can long hours impair a doctor's judgment, they can also put patients' lives at risk.

Doctors are demanding that Hong Kong follow the example set by many other countries and impose a limit on their working hours. The Hospital Authority has responded by proposing a three-year plan to cut their working week to 65 hours. In the meantime, doctors continue to work around the clock.

Hong Kong doctors routinely work up to 80 hours a week depending on their speciality, according to Paul Shea Tat-ming, president of the Public Doctors' Association.

While emergency room physicians work eight-hour shifts, there are no restrictions for other doctors. They are entitled to one rest day a week and between 21 and 30 days annual leave.

Dr Lee, who is on call about eight nights each month, began his marathon shift at 7.25am on Monday. After changing into his scrubs, he checked on 10 patients before stopping for a cup of tea at 8.30am. He saw another 40 patients on the 'grand rounds' of all the hospital's neurosurgical patients and then spent an hour in the out-patient clinic. Working on discharge papers, taking blood, ordering X-rays and CT scans completed his afternoon.

In the early evening, when most Hongkongers were heading home to their families, Dr Lee took a break. 'If you don't have things to do you're getting as much rest as possible because you never know what's going to happen,' he said - adding that incoming emergencies might prevent him from getting much rest.

It may be stating the obvious to suggest that doctors do not perform at their best without sufficient sleep, but a growing body of research indicates the lack of rest is actually endangering patients' lives.

A US study of more than 2,700 medical interns published in December found long working hours were leading to an alarming number of fatigue-related medical errors. The study compared the mistakes made by interns when they worked five or more shifts lasting more than 24 hours each month to when they worked fewer hours.

The interns were four times more likely to make fatigue-related medical errors that resulted in a patient's death when they worked longer shifts, according to researchers from Harvard Medical School and Boston's Brigham and Women's Hospital.

In 2004, the same academics published a study in the New England Journal of Medicine that showed interns made 36 per cent more serious medical errors when they worked 30-hour shifts compared to when they worked 16 hours. They made 5.6 times as many serious diagnostic errors and 21 per cent more serious medication errors. The researchers also found that interns were putting themselves at risk: those who worked 24 hours or more doubled their odds of having a car crash on their way home. The chances of interns sticking themselves with needles or cutting themselves with scalpels was 61 per cent higher among those who worked an average of 29 consecutive hours than those working six consecutive hours.

'Their judgment will be decreased and there's a higher chance of mistakes,' Dr Shea said. 'It increases the risk to the patient.'

Thirty years ago it was accepted that doctors would stoically work non-stop for days, but the technology and sophistication of their work had since increased dramatically, Dr Shea said.

'If the doctor doesn't have a high degree of concentration, just an error in a single digit can be a disaster for the patient,' he said, adding that young doctors bore the brunt of long hours.

In 2004, a case involving a medical intern at the Prince of Wales Hospital demonstrated how disaster could strike when doctors were not sufficiently rested.The intern incorrectly labelled a patient's blood, resulting in an elderly woman receiving the wrong blood type. The mistake was revealed when the woman developed a fever and chills about an hour into the transfusion.

The intern told a Hospital Authority investigation panel that he felt tired and had a sore throat on the night he took the blood samples. He also had to share the workload of a sick colleague. The panel concluded that the intern's ill-health could have contributed to his lapse in concentration, but did not think the extra workload accounted for the mistake.

Dr Lee usually gets between three and five hours' sleep when on call, although there are occasional nights when he doesn't rest at all. When he is not needed, he sleeps on a thin mattress on an old examination couch jammed between the wall and a desk in the office he shares with two other doctors.

In the corner beside the door is a sink, where Dr Lee has a quick wash if there is time to spare.

'If I don't have a busy night I will have a shower, but I will try to get the maximum time for sleep. Sleep is more important for me,' he said.

While the health benefits of achieving a balance between work and personal life have been well documented, it seems doctors are struggling to heed their own advice.

Dr Shea said doctors have a lower marriage rate than the rest of the population. After graduating from medical school at about 24 years of age, they have about seven years to complete their training, ensuring they are working and studying intensively until they reach their early 30s, leaving little time to socialise.

'They don't have the time to bring up their families, they don't even have time to date,' he said.

Dr Lee's lifestyle reflects the energy-sapping nature of his work. The single, mid-career surgeon says he would like to see more of his friends and family but often has to use his free time to catch up on sleep. He rarely exercises and usually grabs food on the run. If he doesn't have time to eat at the hospital cafeteria before it closes, he heads downstairs to a convenience store.

'The long hours do affect the social life,' he admits.

Dr Lee believes doctors should not work longer than 24 hours to ensure they can provide the high standard of care demanded by the community, which includes spending more time with patients and relatives. He said this could be achieved by changing work practices, such as reducing doctors' administrative work and redistributing some of their duties to other medical professionals.

'They've shown in England, in Australia, in Europe that they can do it. Why can we not do it? It can be done, but it's just a matter of will.'

Australia has introduced 16-hour shifts for doctors while Britain recommends no longer than 13 hours. The European Working Time Directive limits the working week for all employees to a maximum of 48 hours.

When the directive was introduced in 1998, there was an exemption for junior doctors in Britain, who were commonly working up to 100 hours a week. Restrictions on junior doctors' hours were introduced gradually to ensure the health system remained adequately staffed, according to a British Medical Association spokesman. In 2004, their hours were cut to 58 and the plan is to reduce them to 48 hours by 2009.

While some doctors like the new arrangement, others say their work has become more intensive, the spokesman said. 'They work in shifts of up to 13 hours. The whole period is spent on their feet, then they go home. That's quite an intensive way of working,' he said.

The spokesman said hospitals had had to employ more doctors, but that the National Health Service would need to make major changes to meet the 48-hour target.

Hong Kong's Hospital Authority is hoping to learn from Britain's experience and has sent a delegation to visit British hospitals. An authority spokesman said an internal consultation would be conducted when concrete proposals were drawn up. A committee is expected to make recommendations by July and has set a target of reducing working hours to 65 hours within three years.

But medical sector legislator Kwok Ka-ki would like to see a 44-hour week.

'It depends on how much commitment the government or the Hospital Authority is putting on relieving working hours. They need to put in more resources. They need to hire more frontline doctors,' Dr Kwok said.

Back at the Queen Elizabeth Hospital, Dr Lee is writing up the last of the day's notes. After more than 30 hours on duty, he plans to catch up with a colleague over dinner before heading home for a well-earned rest. In the morning he'll be back to do it all again.