Low blood oxygen tension, or hypoxemia, occurs in a variety of critical illnesses, such as airway obstruction and acute respiratory distress syndrome, and is associated with increased mortality.

In the past, doctors have tried to treat low levels of oxygen in the blood by injecting free oxygen gas directly into the bloodstream. This can be dangerous, however, because the free oxygen gas can accumulate into larger bubbles and form potentially lethal blockages called pulmonary embolisms. In a new study, researchers oxygenated the blood using newly developed oxygen-filled microparticles and were able to keep rabbits with obstructed airways alive for up to 15 min (Sci. Transl. Med. 4, 140ra88; 2012).

The microcapsules developed by Francis X. McGowan, Jr., and colleagues at Children's Hospital Boston (MA) consist of single-layer spherical shells of lipids, each surrounding a small bubble of oxygen gas. The gaseous oxygen is thus contained and so cannot form larger bubbles. These microcapsules are made by exposing the lipid components to sonic sound waves in an oxygen environment, a process called sonication. The scientists were able to make microparticles containing up to 90% oxygen gas. The most stable of these exhibited 20% loss in 2 weeks, though the researchers suggest ways in which the shelf-life may be improved once the particles are made.

To confirm that the microparticles worked, the researchers first mixed a foam suspension of the particles with human blood in tubes. Once the microparticles were injected, they mingled with circulating red blood cells. The oxygen transferred into the blood cells within seconds of contact, while the remaining lipids were simply reabsorbed by the body. Next, they tested the efficacy of the microparticles in living animals, administering them to asphyxiated rabbits. The injected rabbits survived for up to 15 min, had normal blood pressure and heart rate and did not experience any damage to major organs.

While it may be possible to increase survival time to up to 30 min, any longer would require continually infusing fresh microparticles into the blood, which presents new dangers. This technique is therefore better suited to emergency situations than to long-term life support.

This approach to oxygenating the blood while bypassing the lungs could save the lives of people with impaired breathing or obstructed airways and could prevent cardiac arrest and brain injury induced by oxygen deprivation. Though the researchers caution that further refinements to the technique are needed, the microparticles offer a valuable future intervention for hypoxemia.