hypodermic needle

Different bevels on hypodermic needles.

Syringe on left, hypodermic needle with attached colour coded Luer-Lok connector on right.

A hypodermic needle is a hollow needle commonly used with a syringe to inject substances into the body or extract liquids from the body. They may also be used to take liquid samples from the body, for example taking blood from a vein in venipuncture.

A hypodermic needle is used for rapid delivery of a drug, or when the injected substance cannot be ingested, either because it would not be absorbed (as with insulin), or because it would harm the liver (as with testosterone). There are many possible routes for an injection.

Manufacture

Hypodermic needles are normally made from a stainless-steel tube^[1] drawn through progressively smaller dies to make the needle. The end is bevelled to create a sharp pointed tip. This lets the needle easily penetrate the skin.

Needle gauge

6 hypodermic needles on luer connectors; from top to bottom: 26G x 1/2" (0.45 x 12mm) (brown), 25G x 5/8" (0.5 x 16mm) (orange), 22G x 1 1/4" (0.7 x 30mm) (black), 21G x 1 1/2" (0.8 x 40mm) (green), 20G x 1 1/2" (0.9 x 40mm) (yellow), 19G x 1 1/2" (1.1 x 40mm) (white). See also needle gauge comparison chart.

The diameter of the needle is indicated by the needle gauge. Various needle lengths are available for any given gauge. There are a number of systems for gauging needles, including the Stubs Needle Gauge, and the French Catheter Scale. Needles in common medical use range from 7 gauge (the largest) to 33 (the smallest) on the Stubs scale. Twenty-one-gauge needles are most commonly used for drawing blood for testing purposes, and sixteen- or seventeen-gauge needles are most commonly used for blood donation, as they are large enough to allow red blood cells to pass through the needle without rupturing (this also allows more blood to be collected in a shorter time). Larger-gauge needles (with smaller diameter) will rupture the red blood cells, and if this occurs, the blood is useless for the patient receiving it^[2]. Although reusable needles remain useful for some scientific applications, disposable needles are far more common in medicine. Disposable needles are embedded in a plastic or aluminium hub that attaches to the syringe barrel by means of a press-fit or twist-on fitting. These are sometimes refered to as "Luer Lock" connections.Luer Taper

Non-specialist use

Hypodermic needles are usually used by medical professionals (physicians, nurses, paramedics), but they are sometimes used by patients themselves. This is most common with type one diabetics, who may require several insulin injections a day^[3]. It also occurs with patients who have asthma or other severe allergies. Such patients may need to take desensitization injections; or they may need to carry injectable medicines to use for first aid in case of a severe allergic reaction. Such patients often carry a syringe loaded with epinephrine (e.g. EpiPen)^[4]; some also carry syringes loaded with Benadryl and Decadron. The rapid injection of these drugs may stop a severe allergic reaction, prevent anaphylactic shock, and make an emergency room trip unnecessary, although it may be disconcerting to spectators. Hypodermic needles are also used in recreational intravenous drug use, and to limit the spreading of blood born diseases like Hepatitis and HIV through sharing of injection equipment, many countries now have Needle exchanges in most of their larger cities. Though the dispensing of hypodermic syringes used to be limited to those with a prescription in most countries, nowadays the large majority of countries allow the dispensing of hypodermic syringes without a prescription, and are often even government subsidised through needle exchange programs.

Industrial use

Disposable plastic syringes equipped with unbeveled blunt-tip needles are often used in industry to apply precise amounts of lubricants, adhesives, and various other liquids and pastes.

Phobia

It is estimated that about 10% of the adult population may have a phobia of needles (trypanophobia), and it is much more common in children.^[5]

See also

• cannula
• catheter
• intravenous therapy
• needle biopsy
• needle gauge comparison chart
• needle remover
• Tuohy needle

References

External links

• The Needle Phobia Information Site
• Needle Phobia and Dental Injections