Starting an IV (intravenous line) involves selecting the right vein, inserting a catheter at the correct angle, and securing it so fluids or medications can flow directly into the bloodstream. It’s one of the most common clinical skills in healthcare, and success depends more on preparation and vein selection than on the needle stick itself. Here’s a step-by-step breakdown of the entire process.
Gather Your Supplies First
A standard IV start kit contains a tourniquet, an alcohol prep pad, an antiseptic pad (usually povidone-iodine), two pieces of non-woven gauze, a transparent adhesive dressing, and a roll of medical tape. You’ll also need gloves, the IV catheter itself, a saline flush syringe, and whatever tubing or extension set connects to the fluid bag. Having everything within arm’s reach before you touch the patient prevents the scramble of holding a catheter in place while searching for tape.
Choosing the Right Catheter Size
IV catheters are measured in gauge, and the numbering is counterintuitive: a smaller gauge number means a larger needle. The size you choose depends entirely on what needs to go through it.
- 14G or 16G: Large-bore catheters used in trauma or surgery, capable of delivering 180 to 240 mL per minute for rapid fluid resuscitation.
- 18G: The standard for blood transfusions and fluid resuscitation, flowing at about 90 mL per minute.
- 20G: The workhorse for routine IV fluids and medications, delivering around 60 mL per minute. Most radiology departments also require at least a 20G for IV contrast studies.
- 22G: Suited for elderly patients, pediatric patients, or slower infusions, at roughly 35 mL per minute.
- 24G: Reserved for neonates or very fragile veins, flowing at about 20 mL per minute.
The general rule is to use the smallest catheter that still meets the patient’s clinical needs. A bigger catheter irritates the vein more and increases the chance of complications.
Finding the Best Vein
Vein selection is the single biggest factor in whether an IV start goes smoothly. The nondominant arm is preferred because it’s more comfortable for the patient, less likely to get bumped or pulled, and carries a lower risk of clotting complications.
Start looking distally (toward the hand) and work your way up. The veins on the back of the hand are a common first choice, followed by the forearm veins that run along the thumb side (cephalic) and the inner side (basilic). The veins near the inner elbow (antecubital fossa) are large and easy to find, but placing an IV there limits arm movement and increases the risk of the catheter kinking or dislodging.
The ideal vein feels spongy and springy when you press on it, runs in a straight path, and sits away from branching points where valves tend to cluster. A vein that feels hard or rope-like is likely clotted and won’t work. If you feel a pulse, you’re on an artery, not a vein.
When Veins Are Hard to Find
Some patients present a real challenge: people with obesity, those who’ve had extensive chemotherapy, frequent IV drug users, patients in shock, or people with darker skin tones where veins aren’t as visible. A few techniques help. Apply a warm compress to the area for three to four minutes to dilate the veins. Let the arm hang below heart level so gravity pools blood in the extremity. Have the patient open and close their fist repeatedly. Double-tourniquet technique, where you place one tourniquet above the elbow and another on the forearm, can also help engorge smaller veins. Vein finders that use near-infrared light are increasingly available in clinical settings for truly difficult access.
Preparing the Skin
The CDC recommends cleaning the insertion site with 70% alcohol, tincture of iodine, or chlorhexidine with alcohol before placing a peripheral IV. The critical step most people rush is letting the antiseptic dry completely before inserting the catheter. Wet antiseptic on the skin hasn’t finished killing bacteria, and inserting through it can actually introduce the solution into the tissue. Follow the manufacturer’s listed dry time, which is typically 30 seconds for alcohol and up to two minutes for chlorhexidine. Clean in a circular motion from the center of the site outward, and don’t touch the area again after prepping it.
Inserting the Catheter
Apply the tourniquet three to four inches above the intended site, tight enough to obstruct venous return but not so tight that you can’t feel a pulse at the wrist. The vein should plump up visibly within a few seconds.
Anchor the vein by pulling the skin taut with your non-dominant hand, about an inch below the insertion point. This keeps the vein from rolling sideways when the needle touches it. Hold the catheter with the bevel (the angled opening of the needle) facing up, and enter the skin at roughly a 10 to 30 degree angle. A shallower angle works for superficial veins, while deeper veins need a steeper approach.
Watch the flash chamber on the catheter. When the needle enters the vein, blood will appear in this small transparent section. This “flashback” confirms you’re in the right place. Once you see it, lower the angle of the catheter so it’s nearly parallel with the skin, advance the needle another one to two millimeters to make sure the plastic catheter tip is also inside the vein, then slide the catheter forward off the needle and into the vein. The catheter should glide in with little resistance. If it doesn’t advance easily, don’t force it.
Release the tourniquet before you connect tubing or flush the line. Apply gentle pressure over the vein just above the catheter tip to prevent blood from flowing back out while you remove the needle and attach the extension set or tubing. Activate the needle’s safety mechanism immediately and dispose of it in a sharps container. Flush with a prefilled saline syringe to confirm the line flows freely and the skin around the site doesn’t swell.
Securing the IV
A well-placed IV that isn’t secured properly will fail. Transparent adhesive dressings are the standard because they let you monitor the insertion site for redness or swelling without removing the dressing. A Cochrane review found that transparent dressings resulted in significantly fewer accidental dislodgements compared to gauze dressings. Newer bordered versions with extra adhesive strips along the edges provide additional hold.
Place the transparent dressing directly over the insertion site so the catheter hub is visible underneath. Use additional tape to secure the tubing in a loop near the site so that any tug on the line pulls the tape, not the catheter. In pediatric patients or anyone who moves a lot, splinting the nearby joint (wrist or elbow) with an arm board prevents bending that could kink or dislodge the catheter. For infants under two years, scalp veins on the forehead or temple are sometimes used when limb veins aren’t accessible.
Monitoring for Complications
Check the IV site regularly, at minimum every time you administer a medication or adjust the flow rate. The most common problems are straightforward to spot if you know what to look for.
Infiltration happens when the catheter slips out of the vein and fluid leaks into surrounding tissue. The area around the site becomes swollen and cool to the touch, the skin feels tight, and the IV may slow down or trigger pump alarms. Stop the infusion and remove the catheter. A new IV will need to be started at a different site.
Phlebitis is inflammation of the vein. You’ll notice redness, warmth, and pain along the path of the vein, sometimes with visible streaking. Mechanical phlebitis, caused by the catheter irritating the vein wall, can sometimes be managed by stabilizing the catheter, applying warmth, and elevating the limb. If redness persists beyond 24 hours, or if you see pus at the site, the catheter needs to come out. Purulent drainage should be cultured to check for infection.
Extravasation looks similar to infiltration but involves caustic medications that damage tissue. In addition to swelling, you may see blistering, intense burning, or skin discoloration. This is more urgent. Stop the infusion immediately and try to aspirate any remaining medication from the catheter before removing it.
Nerve injury causes a sharp, shooting, or electric-type pain during insertion or while the catheter is in place. If a patient reports this sensation, remove the catheter right away.
When to Replace the IV
Current CDC guidelines do not recommend routinely replacing a peripheral IV on a fixed schedule (such as every 72 or 96 hours) as long as the site looks healthy and the line functions properly. Instead, the standard is to assess the site at regular intervals and replace the catheter when clinical signs of a complication appear, when the line stops working, or when it’s no longer needed. That said, individual hospitals may still have their own replacement policies, so follow the protocol at your facility.
Tips That Improve First-Stick Success
Confidence and technique develop with practice, but a few principles consistently help. Choose your vein before you pick up the catheter. Palpation matters more than visualization: a vein you can feel but can’t see is often a better target than one that looks prominent but feels flat. Anchor the skin firmly so the vein can’t roll. Go slowly on the initial puncture and watch for flashback before advancing. If you miss, don’t dig around under the skin hunting for the vein. Withdraw and try a fresh site with a new catheter. Most facilities limit attempts to two per clinician before calling someone with more experience or requesting a vein-finding device.