Giving patients extra oxygen during and after surgery can halve the chance of them developing nausea as a result of general anaesthesia, say US researchers.

As many as seven out of 10 people are thought to experience nausea after general anaesthesia, but two studies in the journal Anaesthesiology suggest this can be dramatically reduced without any significant side effects.

The research by the University of California in San Francisco and at hospitals in Vienna found that increasing the level of oxygen in anaesthesia gas during surgery and two hours afterwards halved sickness.

The research was conducted on 231 colon surgery patients in Vienna. Half were given 30% oxygen, considered the normal level, and half were given 80%.

Normally the only solution for combatting post-anaesthesia nausea is anti-nausea drugs.

However, these are only given to people who are vomiting and they only stand a 50% chance of working.

In addition, they cost $30 a go while oxygen is almost cost free.

Researchers also found that it had no side effects and could be given to all patients.

Dr Daniel Sessler, professor of anesthesia and perioperative care at the University of California and senior author of both studies, said: "The take-home message from the new studies is that extra oxygen is cheap, risk-free and reduces the incidence of nausea as well as any known drug."

Life-threatening

The researchers are not sure why extra oxygen has this effect, but they speculate that it may be because the intestines do not get enough oxygen during surgery because of organ interference and cutting.

This could lead to the body believing it is experiencing a life-threatening problem, triggering chemical messengers which cause nausea, they say.

The research is part of ongoing studies by an international science team, the Outcomes Research Group.

It is looking at accepted practice in anaesthesiology to determine if simple improvements can produce major benefits.

For example, previous research led by Dr Sessler found that general anaesthesia lowered body temperature and that keeping patients' bodies warmer could cut the rate of post-operative infection threefold.

This procedure has now become standard practice during general anaesthesia.