Butterfly needle A winged infusion set—also known as "butterfly" or "scalp vein" set—is a device specialized for

venipuncture In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous blood sampling (also called ''phlebotomy'') or intravenous therapy. In healthcare, this procedure is performed by medical labor ...

: i.e. for accessing a

superficial vein Superficial veins are veins that are close to the surface of the body, as opposed to deep veins, which are far from the surface. Superficial veins are not paired with an artery, unlike the deep veins, which are typically associated with an art ...

artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

for either

intravenous injection Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutri ...

phlebotomy Phlebotomy is the process of making a puncture in a vein, usually in the arm, with a cannula for the purpose of drawing blood. The procedure itself is known as a venipuncture, which is also used for intravenous therapy. A person who performs ...

. It consists, from front to rear, of a

hypodermic needle A hypodermic needle (from Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)), one of a category of medical tools which enter the skin, called sharps, is a very thin, hollow tube with one sharp tip. It is commonly used ...

, two bilateral flexible "wings", flexible small-bore transparent tubing (often 20–35 cm long), and lastly a connector (often

female Female ( symbol: ♀) is the sex of an organism that produces the large non-motile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction. A female has larger gametes than a male. Fema ...

Luer). This connector attaches to another device: e.g.

syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

holder/hub, or extension tubing from an

infusion pump An infusion pump infuses fluids, medication or nutrients into a patient's circulatory system. It is generally used intravenously, although subcutaneous, arterial and epidural infusions are occasionally used. Infusion pumps can administer flu ...

or gravity-fed

infusion Infusion is the process of extracting chemical compounds or flavors from plant material in a solvent such as water, oil or alcohol, by allowing the material to remain suspended in the solvent over time (a process often called steeping). An in ...

/ transfusion bag/bottle. Newer models include a slide and lock safety device slid over the needle after use, which helps prevent accidental needlestick injury and reuse of used needles, which can transmit

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

such as HIV and

viral hepatitis Viral hepatitis is liver inflammation due to a viral infection. It may present in acute form as a recent infection with relatively rapid onset, or in chronic form. The most common causes of viral hepatitis are the five unrelated hepatotropic vi ...

Use

During venipuncture, the butterfly is held by its wings between thumb and index finger. This grasp very close to the needle facilitates precise placement. The needle is generally inserted toward the vein at a shallow angle, made possible by the set's design. When the needle enters the vein, venous blood pressure generally forces a small amount of blood into the set's transparent tubing providing a visual sign, called the "flash" or "flashback", that lets the practitioner know that the needle is actually inside of a vein. The butterfly offers advantages over a simple straight needle. The butterfly's flexible tubing reaches more body surface and tolerates more patient movement. The butterfly's precise placement facilitates venipuncture of thin, "rolling", fragile, or otherwise poorly accessible veins. The butterfly's shallow-angle insertion design facilitates

of very

superficial veins Superficial veins are veins that are close to the surface of the body, as opposed to deep veins, which are far from the surface. Superficial veins are not paired with an artery, unlike the deep veins, which are typically associated with an arte ...

, e.g. hand, wrist, or scalp veins (hence name "scalp vein" set).

Needle size

Butterflies are commonly available in 18-27

gauge Gauge ( or ) may refer to: Measurement * Gauge (instrument), any of a variety of measuring instruments * Gauge (firearms) * Wire gauge, a measure of the size of a wire ** American wire gauge, a common measure of nonferrous wire diameter, es ...

bore,Winged infusion Sets , Air-Tite Products
/ref> 21G and 23G being most popular. In

, there is widespread avoidance of 25G and 27G butterflies based on belief that such small-bore needles hemolyze and/or

clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...

blood samples and hence invalidate

blood tests A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a choles ...

. Contrary to this belief, theoretical calculation and ''

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called " test-tube experiments", these studies in biology a ...

'' experiment both showed the exact opposite: namely, that

shear stress Shear stress, often denoted by ( Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on ...

and hence

hemolysis Hemolysis or haemolysis (), also known by several other names, is the rupturing ( lysis) of red blood cells (erythrocytes) and the release of their contents ( cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in viv ...

''decrease'' with decreasing needle bore (but the decrease can be clinically insignificant). In agreement with these results, a subsequent

clinical trial Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, diet ...

found that 21G, 23G, and 25G butterflies connected directly to

vacuum tubes A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as a ...

caused the same amount of

and gave the same coagulation panel test results.

References

{{Reflist Medical equipment