People associate doctors with many things. By far, the objects most commonly associated with doctors are... needles.

Small needles. Fat needles. Long needles. Short needles. It doesn't really matter. No one likes them. For those who really don’t like them, this fear is called belonephobia.

Doctors use needles for lots of reasons:

• Removing fluid or small bits of tissue from within the body or beneath the skin
• Injecting medicines or fluids beneath the skin or directly into the bloodstream
• Poking holes in you, to make entry points for larger plastic tubes

Needles are sized by "gauge" (how big around it is). Usually larger gauge numbers mean smaller diameters (but not necessary shorter needles).

What most patients don’t know is that a doctor’s specialty has a direct correlation with the type and size of needle they use.

The dermatologist

Even though they work on the largest organ of the body (the skin), it seems everything's smaller in dermatology: warts, skin tags, basal cells. And dermatologists don't like scars. When they remove some of your problematic skin, they give you a little local anesthesia, using -- you guessed it -- a tiny 25-gauge needle. (See Figure 1: Dermatology Needle.)

The pediatrician or oncologist

These guys have a knack for flare, but they're still dealing with tiny veins, so they've devised the cutest of the needles, called the "butterfly" needle. (See Figure 2: Butterfly Needle.)

The internist

Nothing can be simple for internists, so the "Angiocath IV" was invented. It's a smaller needle attached to a thin plastic tapered tube that follows the needle into the vein, provided, of course, the doctor was trained earlier by a really good nurse.

Otherwise, the plastic tube will rest outside the vein and let intravenous (IV) fluids pour into the space beneath the skin, swelling the hand to the size of a small softball.

So placing IVs takes a moderate amount of skill and a steady hand. (See Figure 3: IV Needle.)

The orthopedist

With a strong arm and a heavy hand, an orthopedic doctor can reach just about anywhere in the body with a thicker, sturdy, 18-gauge needle. (See Figure 4: Orthopedic Needle.)

The cardiologist

By far, the workhorse needle is the Cook, or Seldinger, needle. Like the orthopedist’s needle, it is also 18-gauge. Its longer length, however, helps the doctor reach the femoral artery in the upper leg. (Yes, the cardiologist could reach this with the orthopedist’s shorter needle, but they don't like to push so hard). This needle's thinner wall and larger diameter allows a thin wire passing through it to reach the artery. The doctor then removes the needle, in order to pass a short plastic straw-like structure (called a "sheath") over the wire into the artery. For such a novel task, it has a strong, commanding look. (See Figure 5: Cook Needle.)

The emergency room physician

Not to be outdone by the meager cardiologist, the emergency room (ER) doctor’s trademark needle is the spinal needle. It's a bit longer than the cardiologist's needle and handy, so the ER doctor can puncture the lower back and enter the spinal canal (getting lightheaded yet?). (See Figure 6: Spinal Needle.)

The cardiac electrophysiologist

But ER doctors have nothing on me, an electrophysiologist. Poking a hole in the heart by passing it up from the upper leg area takes a very special needle. We use this needle to perform atrial fibrillation ablation procedures in the left atrium -- to stop the cause of a heart arrhythmia (abnormal heartbeat). It is the workhorse of today's electrophysiologist. Pioneered by E.C. Brockenbrough to puncture from the right atrium to the left atrium, this needle is the granddaddy of them all.

And what can I say, except... mine's bigger. (See Figure 7: World’s Biggest Needle.)

You see, ladies and gentlemen, size does matter.

Westby G. Fisher, MD, FACC, is a board certified internist, cardiologist, and cardiac electrophysiologist (specializing in heart rhythm disorders) practicing at Evanston Northwestern Healthcare, Evanston, IL. This article, originally posted here, is reprinted with permission. Reach Dr. Wes at featuredstories@adamcorp.com.