What Are Butterfly Needles?

A butterfly needle, also known as a scalp vein set or winged infusion set, is a device used to draw blood from a vein or deliver intravenous (IV) therapy to a vein. A butterfly needle consists of a very thin needle, two flexible “wings,” a flexible transparent tubing, and a connector.

Butterfly needles have advantages over straight needles when collecting blood or delivering IV fluid or medications. For instance, they allow for more precise placement, particularly in hard-to-access veins. There are cases in which other needles need to be used, though.

This article will review the butterfly needle, instances in which they are used, as well as some advantages and disadvantages to the needle.

What Butterfly Needles Are Used For

Butterfly needles have a few different purposes, all of which are temporary.

Blood Draw

Phlebotomists (people who draw blood) regularly use butterfly needles to obtain blood samples for blood-based tests.

Hydration

Butterfly needles can also be used to deliver intravenous fluids if you are dehydrated and either cannot drink fluids or cannot drink enough to compensate for fluid loss.

In some older people, or people receiving end-of-life care who need hydration, butterfly needles can be used subcutaneously (beneath the skin).

Medication

Butterfly needles are useful for delivering medications (such as pain medications) straight into a vein or infusing IV therapies (such as chemotherapy or antibiotics) intravenously.

Types

While all butterfly needles are similarly designed, there are variations. Butterfly needles are measured in gauges and typically range in size from 18 gauge to 27 gauge. The higher the gauge, the smaller the needle.

By way of illustration, a 27-gauge needle is the size commonly used for insulin injections. Smaller gauge needles are used if an injectable fluid is thick or if blood is being collected for transfusion. Most butterfly needles are no more than 3/4 of an inch (19 millimeters).

The IV equipment or collection container is attached to tubing that’s connected to the needle, rather than being directly connected to the needle. This is helpful, as there is less chance of injury if either is yanked or dropped.

Tubing can range in size from 8 inches to 15 inches (20 to 35 centimeters). Shorter tubes are used for blood draws; longer ones are intended for IV applications and may have roller valves to regulate the flow. The tubes may also be colored so that healthcare providers can differentiate the lines if more than one is used.

Some butterfly needle connectors have built-in ports that can be inserted into vacuum tubes. Other connectors have ports into which syringes or lines can be inserted.

How Butterfly Needles Are Used

During venipuncture (the insertion of a needle into a vein), a phlebotomist or nurse will hold the butterfly needle by its wings between the thumb and index finger. Because the hypodermic needle is short and the grasp is close to the needle, the butterfly needle can be placed more accurately than a straight needle, which can often roll or wiggle.

The short, thin needle is inserted toward a vein at a shallow angle. Once inserted, the venous pressure will force a small amount of blood into the transparent tubing, providing confirmation that the needle is correctly placed.

The wings can also serve to stabilize the needle once it is in place, preventing it from rolling or shifting.

Once used (for drawing blood or delivering medication), the entire unit is thrown away in a sharps disposal container. The puncture wound is then bandaged.

Advantages

Because of their small size (far smaller than an intravenous catheter) and shallow-angle design, butterfly needles can access superficial veins near the surface of the skin while causing less pain.

Its use also allows access to small or narrow veins, such as those in infants or older people. On the other hand, they may be more likely to cause needlestick injuries in healthcare providers than other types of needles. Newer models have a slide-and-lock sheath that automatically slides over the needle as it is extracted from a vein.

Butterfly needles are ideal for people with small or spastic (rolling) veins, and can even be inserted into the tiny veins of the hand, foot, heel, or scalp.

They are also ideal for people who are hesitant about needles because they are less threatening, and they are less likely to cause profuse vein injury or nerve injury, especially when using a smaller butterfly needle.

Disadvantages

Butterfly needles are not for everyone.

Because of their small needle size, blood collection tends to be slower. This can be problematic at a blood bank if a person is squeamish or in urgent situations where blood or fluid is needed quickly. In cases like these, the selection of the needle size is key.

Even for a routine blood draw, the wrong needle size can result in blockage and the need for a second draw if a large quantity of blood is needed.

Because a needle is left in the arm rather than a catheter or PICC line for the purpose of an infusion, a butterfly needle can damage a vein if the unit is suddenly yanked. Even if the right size needle is used, the needle can become blocked during treatment if not correctly placed.

As a rule of thumb, butterfly needles should only be used for IV infusions of five hours or less.

Summary

Butterfly needles can be a useful way to draw blood or to give IV fluids. They're especially helpful in people with fragile veins, like children and older people, and in those who are intimidated by needles.

The butterfly needles also can be used beneath the skin in some cases, such as at-home hydration for cancer patients or in long-term care facilities. They're not designed for long-term use, though, and should only be inserted for a few hours or days (depending on the cause).

Check with the healthcare team if you think a butterfly needle is a better option for your blood draw or other procedure.