The device most people call an “IV needle” is formally known as a peripheral intravenous catheter, sometimes shortened to PIV or PIVC. You’ll also hear it called an IV cannula or, in older terminology, an angiocatheter. The name surprises many people because the device that stays in your vein isn’t actually a needle at all. It’s a short, flexible plastic tube. The needle is only used for the initial puncture, then it’s pulled out and discarded, leaving just the soft catheter behind.
How a Peripheral IV Catheter Works
The device comes as a single assembly with two main parts. A thin, laser-sharpened needle sits inside a flexible plastic tube. On top is a color-coded hub that stays above the skin, and behind the needle is a small transparent chamber called a flash chamber. When a nurse punctures your vein, blood flows back into that flash chamber, confirming the needle is in the right place. The nurse then slides the plastic catheter forward into the vein and pulls the needle out entirely. What remains is just the hollow, flexible tube connected to the hub, which gets taped to your skin and attached to IV tubing.
This design is called an “over-the-needle” catheter because the plastic tube sits over the needle during insertion. An older style, the “through-the-needle” catheter, threads a thinner tube through a larger needle. The over-the-needle approach creates a tighter seal at the skin, reducing leakage and the chance the catheter shifts out of position. It’s the standard for virtually all routine IV access today.
Gauge Sizes and Color Coding
IV catheters come in standardized sizes measured by gauge, ranging from 14G (the largest) to 26G (the smallest). The gauge number works in reverse: a lower number means a wider tube. Each size is identified by a universal color on the hub, so healthcare workers can tell at a glance what’s in your vein.
- Orange (14G): The widest option, used in emergencies or trauma when fluids need to flow as fast as possible.
- Gray (16G): Common for surgery or blood transfusions.
- Green (18G): A general-purpose size for most adult IV fluids and medications.
- Pink (20G): Frequently used for standard treatments in adults.
- Blue (22G): Suited for children or adults with smaller veins.
- Yellow (24G): Typically reserved for infants or very fragile veins.
Larger gauges allow faster flow rates, which matters when someone needs rapid fluid resuscitation. For routine medications or hydration, smaller gauges work fine and cause less discomfort going in.
The Butterfly Needle
A butterfly needle is a different device, formally called a winged infusion set (or sometimes a scalp vein set). Unlike a standard IV catheter, a butterfly needle is an actual steel needle that stays in the vein during use. It has two flat plastic “wings” on either side that make it easier to grip and stabilize. Thin tubing runs from the needle to a collection vial or syringe.
Butterfly needles are ideal for quick blood draws or short treatments lasting no more than a few hours. They work especially well for infants, older adults, and anyone with fragile or hard-to-find veins. They can’t stay in long term, though, because the rigid steel tip can irritate or collapse the vein.
Specialized IV Access Devices
Not every IV catheter is the short peripheral type. When someone needs IV access for days or weeks rather than hours, longer devices come into play. Midline catheters are 15 to 25 cm long and are inserted into a vein in the upper arm, threading further up but stopping short of the chest. Peripherally inserted central catheters, called PICC lines, are even longer and extend all the way to a large vein near the heart. Both use the same basic principle: a needle makes the initial puncture, a guide wire or similar tool helps position the catheter, and then the needle is removed.
For patients with an implanted port (a small reservoir placed under the skin, common in chemotherapy), a specialized needle called a Huber needle is used. Its tip curves slightly inward so it doesn’t carve out a tiny plug of the port’s rubber septum each time it’s accessed. This “non-coring” design lets the port be punctured hundreds of times without degrading.
What the Catheter Is Made Of
The flexible tube that sits in your vein is typically made from polyurethane or, in some older models, a material similar to Teflon (PTFE). Polyurethane catheters are softer and more kink-resistant, which matters when the catheter bends with your arm movement. They also cause slightly less vein irritation. An FDA-reviewed analysis of over 15,000 patients found that polyurethane catheters produced phlebitis (vein inflammation) in about 27% of cases, compared to 33% with Teflon-type catheters.
Built-In Safety Features
Modern IV catheters are engineered to protect healthcare workers from accidental needlestick injuries after the needle is removed from your vein. Two main designs exist. Active safety catheters require the user to press a button or clip to retract or shield the needle tip. Passive safety catheters activate automatically as the needle is withdrawn. Both reduce the risk of a contaminated needle poking someone, though nurses generally find passive designs easier to handle since they don’t require an extra step during an already precise procedure.
The concept behind today’s disposable IV catheter dates back to 1950, when an anesthesiology resident named David Massa at the Mayo Clinic described the first plastic over-the-needle design. Before that, metal needles stayed in the vein for the entire infusion, making the experience far more painful and restrictive. Massa’s innovation is essentially the same device, refined with better materials and safety engineering, that goes into millions of veins every day.