Reducing the Risk of Blood Transfusions
Blood is a precious resource. According to the American Red Cross, nearly five million people receive blood transfusions every year. In the US alone, somebody needs blood every two seconds... and the need for blood donations increases every year. As we live longer and improve our ability to treat illness and injury, we use more and more blood. Donations can barely keep up with use -- blood centers often have a hard time maintaining the optimum three-day supply. And, if you need a transfusion, you have the added fear of receiving tainted blood.
But what if somebody could develop a blood substitute -- a way to deliver much-needed oxygen to the body that didn't require the use of real blood -- so that donated blood would only be used when absolutely necessary? And what if that blood substitute didn't need to be refrigerated (and thus re-warmed before use), typed (to match the recipient's blood type) or screened for infectious disease? Simply put, such a substance would change the face of modern medicine -- and would revolutionize emergency medical care. But here's the harsh truth: Scientists have been working on just such a blood substitute since before World War II. And, though modern science has recently brought several products to the FDA for review for approval for widespread use, there isn't a single product currently in development that doesn't have side effects worth questioning. Still, the science is fascinating -- and, since at least two hemoglobin-based products are closer to approval, it's a good idea to know what you could be faced with the next time you need blood.
THE KEY DIFFERENCE -- ORIGINS
So, let's get this out of the way... though the term "blood substitute" is commonly used when referring to these oxygen delivery products, it's a misstatement. While blood has lots of nutrients and beneficial components, blood substitutes don't do anything but deliver oxygen and replace volume, which are the most urgent needs in times of significant blood loss.
Though the end goal is the same, the problem has been tackled a number of different ways -- one of those ways is using hemoglobin from incredibly different origins. One of the two blood substitutes that seems to be among the closest to approval for widespread use, called Hemopure, is made from bovine (cow) blood... another, known as PolyHeme, is made from outdated, human blood (donated blood that was not used within the required 42-day timeframe). One recently abandoned product was made using genetically modified Escherichia coli bacteria -- the researchers modified the bacteria, and the bacteria produced the hemoglobin product.
Still, generally speaking, the same basic technique is used to produce both Hemopure and PolyHeme -- hemoglobin is extracted from the red blood cells (whether from human blood or cow blood), then the hemoglobin is purified (to remove risk of disease), the molecules are chemically linked together to stabilize them (early tests showed that skipping this step caused kidney problems), then the end product is put into a solution. The end result: Products with very long life spans (36 months at room temperature for Hemopure... over 12 months refrigerated for PolyHeme), that can be administered to anyone with no blood typing, and that are free of disease. Seems like a home run, right?
THE PROBLEMS
Well, it isn't exactly. The products have limitations, including the fact that they tend to increase blood pressure dramatically. "If you added a small amount of one of the simple cross-linked hemoglobin molecules to you or me, our blood pressure would go up 20 to 40 mm Hg, so instead of being 120/80, we'd go up to maybe 160/120," says John S. Olson, PhD, Ralph and Dorothy Looney Professor of Biochemistry and Cell Biology at Rice University in Houston, who has been working in the blood substitute field since 1968. "Your doctor wouldn't let you out of the hospital if your numbers were that high." However, the polymerized hemoglobin products from Biopure and Northfield Laboratories are three times larger than a simple hemoglobin molecule and have much smaller, more tolerable blood pressure effects, increases from about 7 to 15 mm Hg. Another large hemoglobin-based product in development by Sangart, Inc., appears to have virtually no blood pressure effect, says Dr. Olson.
Aside from increased blood pressure, some early studies of PolyHeme suggest that the blood substitute could potentially increase the risk of heart attack, though according to a news report in The Wall Street Journal, Northfield Laboratories, Inc. (the company that makes PolyHeme), says that the negative results might have been due to doctor inexperience with the product -- though a definite connection hasn't been made, the doctors could have potentially administered the fake blood plus human blood and the excess total volume of fluids might have lead to heart attacks.
Despite those shortcomings, blood-substitute companies are moving ahead. In a trauma setting, where a patient's blood volume is dangerously low, such side effects could possibly be overlooked because the patient would die without transfusion with an oxygen carrier. "These products only stay in you about eight to 12 hours," Dr. Olson explains, "and that's not a bad thing. The goal is to keep you alive while you're bleeding to death and get you back to the hospital where whole blood could eventually be used."
Then comes the problem of supply... PolyHeme is made from outdated human blood -- ultimately, that blood still needs to come from donations. Hemopure comes from cow blood (though not cows from feedlots), of which there's plenty of supply. But what if the cows in that selected herd become diseased? Though the purification process has been shown to eliminate any risk of transmitting disease to humans, would the disease cause a supply problem if selected cows can't be used? Still, that might be a moot point, because, as Dr. Olson says, the products may only be approved initially for use in certain limited situations. And they certainly aren't going to totally replace donated blood. However, if they are shown to be highly effective, use will expand and then alternative sources will be needed.
WHERE DO WE GO FROM HERE?
Despite their shortfalls, both of these products are likely to be approved by the FDA -- one possibly within the next year for use in special critical situations. (That approval will certainly get the attention of the national media, which has been paying close attention to the field for at least the last decade -- so you're sure to hear about it.) My advice for after that happens: Be prudent. If you are scheduled for surgery, consider you and blood-matched family member(s) donating blood that is specifically held for your use. If that's not possible, talk to your doctor about the blood substitutes, ask about the risks and side effects, and see if they're likely to be used in your area. If you don't like what you hear, ask if there's a way to decline being given the blood substitute -- though in certain trauma situations, you may not have a choice.
The most important thing to remember: These substitutes will never totally replace donated blood -- but it's nice to know there's work in progress to have it available for emergency situations. The need for donated blood is greater now than ever before. Have you given blood recently? If not, you can find a blood drive in your area by visiting www.givelife.org.
from my Daily Health News
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