An IV catheter is a thin, flexible plastic tube inserted into a vein to deliver fluids, medications, or nutrients directly into your bloodstream. It’s one of the most common medical devices in the world, used in everything from emergency rooms to routine outpatient procedures. The plastic tube (called a cannula) stays in your vein while a needle used to guide it in is removed immediately after placement.
How an IV Catheter Is Built
The device has two main parts: a short, hollow plastic tube and a needle that sits inside it. The needle is laser-sharpened and beveled at the tip, designed to pierce the skin and vein wall cleanly. Attached to the back end of the needle is a small transparent chamber called the flashback chamber, which lets the clinician see blood enter when the needle reaches the vein.
Once the needle punctures the vein and blood appears in the flashback chamber, the clinician slides the plastic tube forward off the needle and into the vein. The needle is then pulled out entirely and discarded in a sharps container. What remains is just the soft plastic cannula sitting inside the vein, connected to a hub that stays above the skin. That hub has a standard connector where IV tubing, medication ports, or blood draw adapters can be attached.
What Insertion Feels Like
The needle enters the skin at a shallow angle, typically less than 45 degrees. Most people feel a quick, sharp pinch during the initial puncture, followed by mild pressure as the plastic tube is threaded forward. The whole process takes seconds in experienced hands. Once the needle is out and only the flexible catheter remains, discomfort drops significantly. You may feel occasional pressure or a cool sensation when fluids start flowing, but the catheter itself is soft enough that it bends with your movement.
Cooling sprays have been studied as a way to numb the skin beforehand, but clinical trials in emergency departments found no meaningful difference in pain compared to standard insertion. Traditional numbing creams work but take too long to kick in for most urgent situations. In practice, the brief sting of insertion is over before most topical treatments would take effect.
Catheter Sizes and What They Mean
IV catheters are measured by gauge, and the numbering is counterintuitive: a smaller gauge number means a larger catheter. Each size is color-coded by an international standard so clinicians can identify them at a glance.
- 14 gauge (orange): The largest common size, used for rapid fluid resuscitation in trauma or major surgery.
- 18 gauge (green): A workhorse size for surgeries and situations requiring fast fluid delivery. Flows at roughly 90 mL per minute.
- 20 gauge (pink): The most common all-purpose size, suitable for most medications and IV fluids. Flows at about 60 mL per minute.
- 22 gauge (blue): Used for smaller or more fragile veins, common in elderly patients or those with difficult access. Flows at around 35 mL per minute.
- 24 gauge (yellow): The smallest standard size, often used in pediatrics or for patients with very small veins.
The size chosen depends on what needs to be delivered and how quickly. Someone receiving a simple antibiotic drip might get a 22-gauge catheter, while someone heading into surgery or needing a blood transfusion would likely get an 18-gauge or larger.
Types of IV Catheters
Not all IV catheters are the same length or go to the same place. The type used depends on what’s being infused and how long treatment will last.
Peripheral IV Catheters
These are the short catheters placed in veins of the hand, forearm, or inner elbow. They’re what most people picture when they think of an IV. They work well for standard medications, fluids, and treatments that don’t irritate veins. The CDC recommends considering a longer-term option if IV therapy will likely last more than six days.
Midline Catheters
A midline catheter is longer, around 20 cm, and is inserted into a vein above the elbow using ultrasound guidance. The tip stays in the arm rather than reaching the chest. Midlines are a good option for treatments lasting one to four weeks that use medications safe for peripheral veins. They avoid the risks of a central line while lasting much longer than a standard peripheral IV.
Central Venous Catheters
When medications are too harsh for smaller veins, or when treatment requires rapid dilution in a large blood vessel, a central line is used. One common type, the PICC line, is inserted through a vein in the upper arm but threaded all the way to the junction where the large vein meets the heart. Central lines are used for chemotherapy, concentrated nutrition formulas, and other treatments that would damage smaller veins.
Catheter Materials
Modern IV catheters are made from either a fluoropolymer (commonly called Teflon) or polyurethane. Polyurethane catheters are associated with lower rates of vein inflammation and clotting at the insertion site. Both materials perform equally well across a range of temperatures, so the choice often comes down to institutional preference. Either way, the material is designed to soften slightly at body temperature, reducing irritation to the vein wall over time.
How Long One Can Stay In
A standard peripheral IV catheter can safely remain in place for 72 to 96 hours in adults without increasing the risk of infection or vein inflammation. There’s no benefit to replacing it sooner on a fixed schedule. In children, guidelines recommend replacing the catheter only when there’s a clinical reason to do so, such as signs of a problem at the site, rather than on a set timeline.
In practice, many peripheral IVs are removed or replaced earlier because they stop working properly, the vein becomes irritated, or the catheter gets accidentally dislodged. If longer-term access is needed, a midline or PICC line is a better choice than repeatedly restarting peripheral IVs.
Common Complications to Watch For
The most frequent issue is infiltration, which happens when the catheter tip slips out of the vein or punctures through it, allowing fluid to leak into the surrounding tissue. Signs of infiltration include swelling around the IV site, skin that feels tight or puffy, coolness to the touch, and pain or discomfort near the area. The skin may look pale or reddened compared to the other arm.
Phlebitis, or inflammation of the vein, causes redness, warmth, and tenderness along the path of the vein. It can result from the catheter irritating the vein wall, certain medications, or the beginning stages of infection.
Extravasation is a more serious form of infiltration that occurs when a caustic medication leaks into tissue. It can cause blistering, skin peeling, and tissue damage. If you notice blisters, dark discoloration, pus, or worsening redness and swelling that doesn’t improve within 24 hours, those are signs that need prompt attention from your care team.