A butterfly needle, also called a winged infusion set, is inserted into a vein at a shallow angle of 10 to 15 degrees while you grip the plastic wings between your fingers. It’s the go-to device for patients with small, fragile, or hard-to-access veins, and the technique differs from a standard straight needle in several important ways. Here’s a practical walkthrough of the entire process, from setup to securing the device.
What a Butterfly Needle Is and When to Use One
A butterfly needle is a short, thin needle attached to two flexible plastic “wings” and a length of flexible tubing that connects to either a vacuum tube holder or a syringe. The wings give you a stable grip during insertion, and the tubing adds flexibility so the needle stays put even if the patient moves slightly. These features make the device gentler and typically less painful than a straight needle.
Butterfly needles are used for three main purposes: blood draws, short-term IV fluid delivery, and IV medication administration (pain medication, antibiotics, chemotherapy). They’re the preferred choice for infants, children, older adults, and anyone whose veins are narrow, rolling, or difficult to locate. For patients with large, easily accessible veins, a standard straight needle is usually faster and more practical. Butterfly needles are designed for short-term use, not infusions lasting more than a few hours.
Choosing the Right Gauge
Butterfly needles come in several gauges, and a higher gauge number means a thinner needle. The most commonly used sizes are 21-gauge, 23-gauge, and 25-gauge. A 21-gauge is appropriate for routine blood draws in adults with reasonably sized veins, while a 23- or 25-gauge works better for pediatric patients, elderly patients, or anyone with very small veins. Thinner needles are gentler but draw blood more slowly.
Most manufacturers color-code the wings to indicate gauge size. Common pairings include purple for 21-gauge, orange for 23-gauge, and blue for 22-gauge, but color coding varies between brands. Always check the gauge printed on the packaging rather than relying on color alone.
Preparing the Site and Equipment
Before touching the needle, gather everything you need: the butterfly needle set, collection tubes (in the correct order of draw), a tourniquet, alcohol swabs, gauze, tape, gloves, and a sharps container. Modern butterfly needles are required to include a safety-engineered feature, such as a retractable needle or a shielding mechanism, to prevent accidental needlestick injuries. Confirm that the safety feature is intact and functional before you begin.
Apply the tourniquet a few inches above your target site and ask the patient to make a fist. Identify the vein by sight and palpation. The veins on the back of the hand and the forearm are common targets for butterfly needles, since these are the sites where smaller veins tend to be more accessible. Clean the area with an alcohol swab and let it air dry completely. Inserting through wet alcohol can sting and may contaminate the sample.
Inserting the Needle Step by Step
Pick up the butterfly needle by pinching the two wings together between your thumb and index finger, folding them upward so they form a V-shape you can grip firmly. This is one of the key advantages of the device: the wings give you precise control that a straight needle can’t match.
With your non-dominant hand, pull the skin taut a few centimeters below the insertion point. This anchors the vein and keeps it from rolling. Let the patient know you’re about to insert the needle, then advance it bevel-up at an angle of 10 to 15 degrees. This is noticeably shallower than the 15- to 30-degree angle used with a standard straight needle, and it’s one of the most common mistakes new users make: going in too steeply.
Watch the tubing carefully. When the needle enters the vein, you’ll see a flash of blood appear in the small chamber at the base of the needle and begin traveling through the tubing. This “flashback” is your confirmation of successful venous access. Once you see it, flatten the angle slightly and advance the needle another 3 to 5 millimeters to seat it securely inside the vein. Don’t push further than that, or you risk going through the other side of the vein wall.
Securing the Needle in Place
Once you’ve confirmed access, release the tourniquet (for blood draws, the tourniquet should remain no longer than one minute to avoid affecting results). Unfold the wings flat against the patient’s skin. Place a small cotton ball or gauze pad under the wings to maintain the correct shallow angle, then tape the wings down firmly with medical tape or a clear adhesive dressing.
Tape a loop of the excess tubing to the skin as well, leaving a little slack. This “safety loop” means that if someone accidentally tugs the tubing, the pull is absorbed by the taped loop rather than transmitted directly to the needle. For infusions lasting more than a few minutes, this step is especially important.
Drawing Blood With a Butterfly Needle
If you’re collecting blood into vacuum tubes, attach the tube holder to the end of the tubing and push each tube onto the needle inside the holder. The vacuum in the tube does the work of pulling blood through the tubing. If you’re using a syringe instead, pull back on the plunger slowly and steadily to avoid collapsing the vein.
One critical detail: if your first tube is a citrate tube (blue top, used for coagulation testing), you need to draw a small discard tube first. The tubing contains a pocket of air, and if that air enters the citrate tube, it changes the ratio of blood to anticoagulant and can produce inaccurate results. A 3-mL plain tube with no additive is the standard discard. If your first tube is any other type, this step is typically unnecessary, but always follow your facility’s order-of-draw protocol.
Butterfly needles produce significantly fewer hemolyzed (damaged) blood samples than IV catheters. One large study found a hemolysis rate of just 2.7% with butterfly needles compared to 14.6% from IV catheters. Factors that normally increase hemolysis risk, like small gauge size, difficult venipuncture, or longer tourniquet time, had no measurable effect when a butterfly needle was used. This makes them an especially reliable choice when sample quality matters.
Removing the Needle and Activating Safety Features
When your last tube is full or your infusion is complete, place a piece of gauze over the insertion site without pressing down yet. Withdraw the needle smoothly at the same shallow angle you used to insert it, then immediately apply firm pressure with the gauze. Have the patient keep pressure on the site for at least two minutes (longer if they’re on blood thinners).
Activate the needle’s safety mechanism right away. Depending on the device, this may involve pressing a button that retracts the needle into the tubing, or sliding a shield over the needle tip. Do this before setting the device down. Drop the entire assembly directly into a sharps container. Never recap a butterfly needle by hand.
Common Mistakes to Avoid
- Angle too steep: A butterfly needle should enter at 10 to 15 degrees. Going in at 30 degrees, which works for a straight needle, will often push through the vein entirely.
- Not watching for flashback: The tubing gives you a clear, visible signal that you’re in the vein. If you don’t see blood in the chamber, don’t force it. Reposition or retry.
- Skipping the discard tube: Forgetting to clear the air from the tubing before collecting a citrate tube is a common cause of rejected coagulation samples.
- Not securing the tubing: A butterfly needle without a taped safety loop can be pulled out by any incidental tug on the line.
- Leaving the tourniquet on too long: Tourniquet time beyond one minute can alter blood test results, particularly for potassium and other chemistry values.