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 Sampling (medicine)#blood, blood sampling (also called ''phlebotomy'') or intravenous therapy. In healthcare, this procedure is p ...

: 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 () is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in ...

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 nutr ...

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 a ...

. It consists, from front to rear, of a

hypodermic needle A hypodermic needle (from Greek Language, Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)) is a very thin, hollow tube with one sharp tip. As one of the most important intravenous inventions in the field of drug admini ...

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

female An organism's sex is female ( symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction. A female has larger gametes than a male. Females and ...

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, thermionic 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 voltage, potential difference has been applied. It ...

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 ...

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 inf ...

/ transfusion bag/bottle. Newer models include a slide and lock safety device slid over the needle after use, which helps prevent accidental

needlestick injury A needlestick injury is the penetration of the skin by a hypodermic needle or other sharp object that has been in contact with blood, tissue or other body fluids before the exposure. Even though the acute physiological effects of a needlestick ...

and reuse of used needles, which can transmit

infectious disease An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

such as

HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...

and viral hepatitis.

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

Needle size

Butterflies are commonly available in 18-27

gauge Gauge ( ) 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, especia ...

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 ( thrombi) is a solid or semisolid aggregate from constituents of the blood (platelets, fibrin, red blood cells, white blood cells) within the circulatory system during life. A blood clot is the final product of the blood coagulatio ...

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 cho ...

. Contrary to this belief, theoretical calculation and ''

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

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

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

and hence

hemolysis Hemolysis or haemolysis (), also known by #Nomenclature, 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 ...

''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 subject research, human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel v ...

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

vacuum tubes A vacuum tube, electron tube, thermionic 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 voltage, potential difference has been applied. It ...

caused the same amount of

and gave the same coagulation panel test results.

References

{{Reflist Medical equipment