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    Saturday, November 26, 2005

    History Lessons: On more than one occasion, I've had patients with very severe edema ask me to "just put a needle in there" and suck out the fluid. Once upon a time, that's what they did.

    UPDATE: How come you can't just suck out the fluid?

    Good question. The short answer is because it would just come back. The long answer is very, very long. Swelling in the lower legs like that in the link above is caused by leakage of fluid from the veins into the surrounding soft tissues. Sometimes this happens because the concentration of protein molecules in the fluid in the veins is lower than the concentration in the surrounding soft tissues - so the fluid drifts out to try to achieve equilibrium. (Remember those osmosis experiments from high school?) This is what happens when people are severely malnourished or have liver failure or nephrotic syndrome.

    Sometimes, it happens because the blood vessels or lymphatic channels are missing to carry fluid away from the soft tissues. This is the cause of chronic swelling that sometimes occurs after surgery or a traumatic injury to a limb.

    More commonly, however, the swelling happens because of a pressure back-up between the arteries and the veins in the legs. As we get older, our veins become less elastic, and the little valves in them don't do as good a job of pumping the blood back up to our heart where it belongs. This is most often a problem in the legs because the veins there have to constantly work against gravity. The blood just kind of backs up down there, even as the arteries continue to push fluid into them. The result is that fluid gets pushed out to the soft tissues, causing swelling. The same sort of dynamics occur in cases of congestive heart failure (fluid backs up because the heart isn't pushing the blood forward as it should), and with the use of some drugs, such as calcium channel blockers, which relax the smooth muscle in the vein walls a little too much.

    If we just put a tube in the legs and drained off the fluid, we wouldn't be addressing the root cause of the problem, and it would be right back as quickly as we finished the drainage. So, in cases involving a mismatch between protein molecule concentrations - we try to influence that concentration - sometimes by restricting the amount of fluid a patient can drink, sometimes with diuretics that decrease the amount of fluid in the blood vessels by sending it out the urine via the kidneys, and sometimes with intravenous infusions of a protein called albumin. In the other cases, about all we can do is recommend compression stockings (i.e. support stockings) - or in severe cases, a pump - to try to squeeze the blood back up the leg.

    posted by Sydney on 11/26/2005 08:22:00 AM 0 comments


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