One of the most deadly gases known to mankind may one day be used to save lives.

Scientists have discovered that carbon monoxide (CO) - in the right dose - can trigger the breakdown of blood clots.

They believe that the gas could be used in very carefully controlled conditions to treat patients suffering from a potentially deadly blood clot in the lung.

These clots, known as pulmonary embolisms, are caused by injuries, or damaged arteries.

Carbon monoxide is a colourless, odourless, tasteless gas produced during incomplete combustion of fuel. It is the gas that kills people who commit suicide by feeding exhaust fumes back into their car.

The gas inhibits the ability of the red blood cells to take up oxygen, and transport it to the body's tissues.

However, an enzyme in the body naturally produces a small amount of CO at times when oxygen supply is low.

Mice tests

Dr David Pinsky and colleagues at Columbia University, New York, carried out tests on mice which lacked this enzyme.

They found that the mice recovered after being starved of blood and oxygen if they inhaled CO.

They also found that CO triggers a series of biological reactions which combat inflammation and break down blood clots.

They concluded that at low levels, CO acts to save lung tissue cut off from blood and oxygen by a clot - otherwise known as ischaemic tissue.

Caution urged

Writing in the journal Nature Medicine, the scientists said: "We show here a previously unrecognised mechanism by which CO might effect the rescue of ischaemic tissue."

Dr Pinsky told BBC News Online: "We envision that there might be several potential therapeutic uses for inhaled carbon monoxide, but caution that because of its well-known toxicities when given in excess.

"Doses would need to be carefully monitored and further studies must be performed verifying its efficacy in specific disease conditions before any therapeutic recommendation could be given."

Dr Pinsky said CO treatment might be suitable for stroke or heart attack patients, those undergoing lung transplantation, and those with severe bacterial infections.

He said it might also be useful to give to people prior to operations where there is expected to be an interruption of blood flow, such as coronary artery bypass grafting.

However, Christoph Thiemermann, from the William Harvey Research Institute in London, warned against rushing in to treat lung injury patients with carbon monoxide.

He said: "The dangers of CO inhalation outweigh the benefits."