Listen up: you'll thank yourself for getting one, especially if your particular condition requires not only infusions of Nasty Stuff but also frequent blood tests.
Central lines are, as the name implies, intravenous lines that go into one of the really big veins that drains into the center of the body. They come in three types: Really Temporary, Sorta Permanent, and Really Permanent.
The Really Temporary type is most common if you're having something like plasmapheresis done for CIDP or MS. Normally it's inserted at the bedside by a surgeon, and it goes into the internal jugular vein (that's the big one in your neck). Very occasionally they'll put one into the big vein in your groin, but that's kind of a pain in the ass, so it's to be avoided if at all possible.
Most likely, your IJ (internal jugular) central line will have two separate toggles on it and will be short and sort of curled on the ends. Through this, nurses and doctors can draw blood and do plasma exchanges. It saves you from getting large-bore IVs started every time you need a plasma exchange, and saves you from getting stuck multiple times for blood draws....but there's a drawback: no matter how carefully-inserted the thing is, it has to come out after a week, two weeks at the most.
The Sorta-Permanent type of CL used most often is something called a PICC line. PICC stands for Peripherally-Inserted Central Catheter. It goes into your arm and threads up the big brachial vein, to end just above your heart. PICCs are very handy indeed, as they come in one, two, and three-lumen (opening) versions and can be used for everything from injections of IV contrast (provided they're the right sort) to blood draws to chemotherapy infusions.
PICCs can stay in for weeks to months; I've seen 'em stay in and be usable for six months or more. Generally speaking, though, you want the thing out within about 14 weeks, just to reduce the risk of infection.
The Really-Permanent type of central line is called a Mediport. (This, by the way, is a brand name. Please don't sue me. Thank you.) Mediports are cute little buttons that sit under your collarbone and attach to a line that runs, again, into the big vein above your heart. The advantage of Mediports is that they can stay in basically forever, be used for blood draws and suchlike for years, and don't have as great a risk for infection as the other types of central lines. The drawback, of course, is that you're getting something implanted under the skin of your chest, so you're gonna need anesthesia and stitches and so on. Plus, they're kind of a pain to take out. However, if you're going to need chemo for a long time, like if you have MS and need periodic infusions of Rituxan, they're a good bet.
Mediports are accessed by a stick. That's another drawback if you really hate needles, but hey: it beats getting stuck with enormous needles over and over in one or both arms, right? Right.
The drawbacks of all central lines are pretty much the same: you could get a whopping infection either at insertion or later on. To combat that, they're put in using sterile technique, and everybody's very careful about using them.
Another possible complication is that the line either busts through the vein wall or doesn't go where it ought to, leading to punctured chest cavities, internal bleeding, or other screwy stuff. Luckily, lines are what we call "radio-opaque", which means they'll show up on X-ray. Once they're placed, we can check that they're in the right spot with an X-ray, and reposition that sucker if necessary.
A final complication, and the most common one by far, is that the central line will form what's called a fibrin sheath on the end, so you can neither draw blood nor infuse drugs through it. Fibrin, by the way, is a component of blood clots. When this happens, we have a cool drug called TPA that can dissolve the fibrin, thus making the line usable again. And no, it doesn't mean a clot will go shooting toward your head; it dissolves the blockage into such small pieces that your body doesn't even notice them. I do a LOT of central line declotting at work.
That's your Central Line Primer for the week. Consider asking for one if you're undergoing treatment for MS, MRSA, cancer, or anything that'll require frequent sticks and blood draws. Your peripheral veins will thank you.