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 Kheir, a cardiologist at the 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 avoid cerebral palsy resulting from a compromised fetal blood supply. In the past, 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. They had varying degrees of success, says Kheir.
In the late nineteenth century, for example, US doctor John Harvey Kellogg experimented with oxygen enemas — an idea that has been revived in recent decades 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 procedure would have to be done at dangerously low temperatures. The microcapsules used 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 small bubble of oxygen gas. The gaseous oxygen is thus encapsulated and suspended in a liquid 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 the microparticles 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 forms of artificial blood currently in use, which can carry oxygen around the body, but must still receive it from the lungs.