The number of wound infections following operations dropped by 50% if patients were given more oxygen during surgery, researchers say.

The gas seems to improve the immune system's ability to fight the bacteria which cause the problems.

The research, published in the New England Journal of Medicine, could save the NHS millions, and save lives, if confirmed by other studies.

Patients who develop seriously infected wounds may have to occupy expensive hospital beds for longer - and require more nursing care once they are discharged.

Patients are given oxygen by anaesthetists while they are unconscious during surgery.

At present, the standard mixture given has 30% oxygen, but the researchers, based at the University of California in San Francisco, increased this to 80% oxygen.

They tested 500 patients undergoing surgery either for colon cancer, or from inflammatory bowel disease.

Wound infections developed in 28 of the 250 patients given the normal oxygen mixture, but in only 13 of the patients on the 80% mix.

Six of the patients given conventional oxygen died within 15 days of surgery - but only one in the other group.

Thousands of dollars

Patients who developed wound infections on average required an extra week of hospitalisation, at a cost of $12,500 each.

Medical oxygen, the researchers point out, is one of the cheapest substances used in hospital - costing, in the US, 40 times less than tap water.

It is believed that the technique works by making more oxygen available to cells called neutrophils, which attack and kill invading bacteria.

Mr Alaistair Windsor, a surgeon specialising in colorectal operations at St Marks' Hospital in North London, said that the findings could represent another step forward in wound infection prevention.

He said: "It's an interesting paper, and a simple idea, from a very reliable source. Wound infection is a real burden for the patients, their families, GPs, nurses and for ourselves.

"If it is proved in other trials that adding oxygen can improve the infection rate, that would be significant."

Wound infections - which normally develop when bacteria already carried by the patient comes into contact with a wound - are a major additional cost to the NHS.

Research published earlier this week suggested that hospital-acquired infections - new bugs picked up during a stay on the wards - could be costing the NHS more than �1bn a year.