Rabbits with blocked windpipes have been kept alive for up to 15 minutes without a single breath, after researchers injected oxygen-filled microparticles into the animals' blood.

Oxygenating the blood by bypassing the lungs in this way could save the lives of people with impaired breathing or obstructed airways, says John Kheirm, a cardiologist at tthe Children’s Hospital Boston in Massachusetts, who led the team. The results are published today in Science Translational Medicine1.

The technique has the potential to prevent cardiac arrest and brain injury induced by oxygen deprivation, and to prevent cerebral palsy in fetuses with compromised blood supplies.

In the past efforts, doctors have tried to treat low levels of oxygen in the blood, or hypoxaemia, and related conditions such as cyanosis by injecting free oxygen gas directly into the bloodstream, with varying degrees of success, says Kheir.

In the early twentieth century, US doctor John Harvey Kellogg, for example, experimented with oxygen enemas — an idea that has been revived up relatively recently in the form of bowel infusers2, says Mervyn Singer, an intensive-care specialist at University College London.

But these methods can be dangerous, because the free oxygen gas can accumulate into larger bubbles and form potentially lethal blockages called pulmonary embolisms.

Injecting oxygen in liquid form would avoid this, but the low temperature of liquid oxygen would be harmful. The microcapsules uised by Kheir and his team get the best of both worlds: they consist of single-layer spherical shells of biological molecules called lipids, each surrounding a tiny pocket of oxygen gas. The oxygen is thus in gas form, but is encapsulated and suspended in an emulsion, so can't form larger bubbles.

The particles are injected directly into the bloodstream, where they mingle with circulating red blood cells. The oxygen diffuses into the cells within seconds of contact, says Kheir. “By the time they get to the lungs the vast majority of the oxygen has been transferred to the red blood cells,” he says. This distinguishes these microcapsules from the various form of artificial blood now used, which can carry oxygen around the body, but must still receive it from the lungs.

The lipid foam is also safe, says Kheir. “As the oxygen leaves them, the shell buckles and folds, with the lipids breaking off,” he says. The body then reabsorbs them.

In the experiment, rabbits whose airways had been completely blocked could survive up to 15 minutes without breathing, with normal blood pressure and heart rate, and showed no indication of liver damage caused by oxygen deprivation, nor of any heart or lung damage or pulmonary embolisms.

The microcapsules are also easy and cheap to make, says Kheir. They effectively self-assemble and are formed by exposing the phospholipid components to intense sound waves in a purely oxygenated environment, a process known as sonication.

It’s a very sophisticated approach, says Singer. Heart and lung machines can also oxygenate the blood, as can extracorporeal membrane oxygenation (ECMO), he says. However these are more suited to longer-term life support and would not be much use in acute cases, such as when someone’s trachea was blocked, he says.

Indeed one of the great advantages of this approach is the speed at which it works, says Kheir. However, although Kheir believes it may be possible to extend the 15 minutes to as much as 30 minutes he doubts it could be pushed much further because there are limits on how much additional fluid can be pumped into the bloodstream. “It’s not going to replace the lungs, it just replaces their function for a limited period of time.”