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Tuesday, April 08, 2003The military, he said, supported the development of substances that might help in trauma, like a lightweight salt solution to restore fluids to injured soldiers, but it was never tested in the large clinical trials that are necessary before it can be sold. "They couldn't get anyone to test it, and they couldn't test it themselves," Dr. Champion said. The standard salt solution, Ringer's solution, was developed at least 50 years ago to treat diarrhea. "The standard of care is 1,000 c.c.'s of Ringer's, and if that doesn't work, give another 1,000 c.c.'s," Dr. Champion said. Each 1,000 cubic centimeter package weighs about 2.2 pounds. "That's quite a lot of weight when you're running up a hill under gunfire," he said. ... In Iraq, the Army is testing alternatives, like Hextend, a fluid that does not to be refrigerated and stays in the blood vessels, unlike Ringer's, which seeps out. It appears that a half-liter of Hextend may be the equivalent of three liters of Ringer's. But that equivalence, Dr. Holcomb said, needs to be tested in a large clinical trial, one of the many studies he and others are planning among civilians, who would be given the fluids in ambulances. While hemostatic bandages can stem external hemorrhage, internal bleeding often requires massive amounts of blood transfusions to support life until the bleeding can be stopped. A lightweight alternative to blood would be very welcome, but there remains a lot of work to be done: The concept was simple. Oxygen is carried in blood by hemoglobin, a protein in red blood cells. If you got rid of the cell and just used hemoglobin, it could in theory supply tissues with oxygen on its own. But when researchers tried that approach, it ended in disaster, with injuries to major organs, including the liver and kidneys. A likely reason is that hemoglobin disables a small molecule, nitric oxide, in blood vessels, preventing them from relaxing. With narrowed blood vessels, vital organs do not get enough blood. "The last trial of unmodified hemoglobin was in 1978," Dr. Gould said. Researchers from Warner Lambert gave tiny amounts of the protein to six healthy volunteers. "They saw these toxicities," he said. "It happened 100 percent of the time, to every one of them." Dr. Gould called one of the drug company scientists. "He said: `It's worse than it sounds in the paper. It scared the daylights out of us.' " But it appears that the toxicities disappear if the hemoglobin molecules are linked together in chains. The only problem, Dr. Gould said, is that virtually no small unlinked hemoglobin molecules can be in the mixture. "We gradually started to purify," he said, testing the substance in baboons and finding that he had to go below 1 percent unlinked hemoglobin or the artificial blood was dangerous. With its solution of purified chains of hemoglobin, the company began small studies and was buoyed by success. Doctors have given as much as 20 units, or pints, of the artificial blood, PolyHeme, in 20 minutes, Dr. Gould said. An adult normally has about 10 units of blood. But with a severely injured patient, blood loss can be so rapid that it is lost as quickly as it is given, necessitating transfusions of 20 or even 30 units Larger trials are pending. posted by Sydney on 4/08/2003 08:03:00 AM 0 comments 0 Comments: |
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