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Needles and Radiology Procedures

The sad fact is that in order to get a dye to circulate intravenously, you will have to be stuck with a needle and that hurts. The person assigned to this task varies. It could be the radiologist, the technologist, or the radiology nurse. The basic facts are the same though. With the newer dyes that are a little thicker in consistency, we need bigger needles. If you have bad veins, that is not good news. Most patients who have "bad veins" know that about themselves and know which arm is more productive. Don't be shy about telling the injector.

The inside of the elbow (anticubital fossa) is the best place as far as the pain is concerned. Sometimes the patient doesn't even feel it. However, the problem with that location is that when the arm bends, the IV is put into great risk of infiltrating, which is bad. What we want is for the contrast to flow from the syringe into the needle, which is safely ensconced in your vein, directly in the bloodstream. What we don't want is for the dye to get out into the soft tissues at the site of injection. If the needle or catheter is not cleanly inserted, it may puncture the walls of the vein several times. So even though most of the dye flows where it should, some can get through tears in the wall right into the soft tissues(extravasation).

Extravasations in the era of low osmolarity contrast agents (LOCA) are minor problems. LOCA seems to be much less toxic to the soft tissues than high osmolarity contrast agents (HOCA) used to be. The severe pain that some patients had with HOCA extravasations does not seem to appear at all with LOCA. Still, with good practice, extravasations should be avoided especially those large ones from automatic injectors.

For the inside of the elbow to work with an IV, the doctors now use a flexible needle, one made of plastic and not metal. The so-called angiocatheter, which is simply a metal needle, is fitted with a plastic catheter. Once in the vein, the metal needle is slowly withdrawn while the plastic catheter is advanced further into the vessel. As long as you are not too rambunctious, the catheter will stay in place ,where as a metal needle would have wreaked havoc on the poor vein.

What about using the hand? Ouch! Almost everyone has a decent hand vein or two, and you can actually see them better than in the inside of the elbow. The back of the hand doesn't bend, so the needle can stay in place safely and easily. Sounds perfect. While the hand is an excellent injection site, it hurts more. Also, because there is so little space available, extravasations and black-and-blue marks are more obvious and uncomfortable.

Radiologists have been known to inject contrast agents into veins in the foot and ankle. Actually, before the days of vascular ultrasound, many patients had contrast venograms, where dye was injected into veins in the foot. In rare circumstances, that test is still being done. In any event, injecting dye into a vein in the foot is not without precedent. Each case needs to be studied separately.

The old-fashioned needle was metal, had a shaft with a sharp bezel at one end, and at the other end was attached to a hub that could fit onto the end of syringes. The thickness or thinness of the needle shaft is described by gauge numbers. The lower the gauge, the thicker the needle; the higher the gauge, the thinner the needle. A little 25-gauge needle is so thin that patients often don't even know when the needle is going in. To get blood from you, the technicians in the lab use 19-/or 20-gauge needles attached to some tube system. When you give blood, a 16 gauge needle is used. Stereotactic breast biopsies are done with 11-/or 14-gauge needles, which are large enough to produce a core of tissue.

The problem with using just a needle is that stripped naked they are hard to immobilize. So someone thought of encompassing the hub of the needle into a plastic apparatus that could easily be attached to the skin surface with tape. The colorful little contraption looked very much like a butterfly and has carried that name ever since. Now we have a metal shaft of a certain gauge with a sharp bezel joined to a hub for connection to a syringe and attached to a plastic harness. Once the "wings" of the "butterfly" are taped to the skin, the whole contraption is immobilized nicely.

Try as you may to prevent them, that metal shaft with the sharp bezel is going to get the best of us and cause extravasations of dye. So why not replace the metal with plastic? Well, for one, plastic is too soft and floppy to puncture the skin by itself. But if we insert a smaller metal needle into the plastic one, we have a rigid system. The puncture of the skin will be supported by the rigid metal needle. Once in the vein, the metal needle can be withdrawn leaving just the catheter in place. The less rigid catheter will endure much more motion than the inflexible metal needle.

The price you pay for this flexible tube is a bit more pain. Adding plastic makes the needle thicker by a gauge or two. Also very few people react to the metal needles, but reactions to the plastic are known.

The plastic catheter with a bevel at its tip surrounding a withdrawable metal needle is called intercath and angiocath ,among others, depending on styles and brands. They come in all sizes, gauges, and models, but basically they empower the injector to insert a flexible catheter into a vein.

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