Syringes and needles are sterile devices used to inject solutions into or withdraw secretions from the body. A syringe is a calibrated glass or plastic cylinder with a plunger at one and an opening that attaches to a needle. The needle is a hollow metal tube with a pointed tip.
A syringe and needle assembly is used to administer drugs when a small amount of fluid is to be injected; when a person cannot take the drug by mouth; or when the drug would be destroyed by digestive secretions. A syringe and needle may also be used to withdraw various types of body fluids, most commonly tissue fluid from swollen joints or blood from veins.
The modern hypodermic needle was invented in 1853 by Alexander Wood, a Scottish physician, and independently in the same year by Charles Pravaz, a French surgeon. As of 2003, there are many different types and sizes of syringes used for a variety of purposes. Syringe sizes may vary from 0.25 mL to 450 mL, and can be made from glass or assorted plastics. Latex-free syringes eliminate the exposure of health care professionals and patients to allergens to which they may be sensitive. The most common type of syringe is the piston syringe. Pen, cartridge, and dispensing syringes are also extensively used.
One common type of syringe consists of a hollow barrel with a piston at one end and a nozzle at the other end that connects to a needle. Other syringes have a needle already attached. These devices are often used for subcutaneous injections of insulin and are single-use (i.e., disposable). Syringes have markings etched or printed on their sides, showing the graduations (i.e., in milliliters) for accurate dispensing of drugs or removal of body fluids. Cartridge syringes are intended for multiple uses, and are often sold in kits containing a pre-filled drug cartridge with a needle inserted into the piston syringe. Syringes may also have anti-needlestick features, as well as positive stops that prevent accidental pullouts.
There are three types of nozzles:
A hypodermic needle is a hollow metal tube, usually made of stainless steel and sharpened at one end. It has a female connection at one end that fits into the male connection of a syringe or intravascular administration set. The size of the diameter of the needle ranges from the largest gauge (13) to the smallest (27). The length of the needle ranges from 3.5 inches (8 cm) for the 13-gauge to 0.25 inch (0.6 cm) for the 27-gauge. The needle consists of a hub with a female connection at one end that attaches to the syringe. The bevel, which is a slanted opening on one side of the needle tip, is located at the other end.
Needles are almost always disposable. Reusable needle assemblies are available for home use.
Syringes and needles are used for injecting or withdrawing fluids from a person. The most common procedure for removing fluids is venipuncture or drawing blood from a vein. In this procedure, the syringe and a needle of the proper size are used with a vacutainer. A vacutainer is a tube with a rubber top from which air has been removed. Fluids enter the container without pressure applied by the person withdrawing the blood. A vacutainer is used to collect blood as it is drawn. The syringe and needle can be left in place while the health care provider changes the vacutainer, allowing for multiple samples to be drawn during a single procedure.
Fluids can be injected by intradermal injection, subcutaneous injection, intramuscular injection, or Z-track injection. For all types of injections, the size of syringe should be chosen based on the amount of fluid being delivered; the gauge and length of needle should be chosen based on the size of the patient and type of medication. A needle with a larger gauge may be chosen for drawing up the medication into the syringe, and a smaller-gauge needle used to replace the larger one for administering the injection. Proper procedures for infection control should be strictly followed for all injections.
Syringes and needles are normally sterile products and should be stored in appropriate containers. Care should be taken prior to using them. The care provider should ensure that the needles have not been blunted and that the packaging is not torn, as poor handling or storage exposes the contents to air and allows contamination by microorganisms.
All health care personnel must be offered vaccines against such bloodborne infections as hepatitis B and C.
Used syringes and needles should be discarded quickly in appropriate containers. If a needlestick injury occurs, it must be reported immediately and proper treatment administered to the injured person.
Health care instructors should ensure that staff members are skilled in up-to-date methods of aseptic technique as well as the correct handling and use of syringes and needles. All persons administering injections should be aware of current methods of infection prevention.
Teaching the correct use of syringes and needles, as well as their disposal, is important to protect medical staff and people receiving injections from needlestick injuries and contamination from bloodborne infections. As of 2003, some of the more serious infections are human immunodeficiency virus (HIV), hepatitis B (HBV), and hepatitis C (HCV).
Needles are defined as "sharps" for purposes of public health regulation, and must be broken or otherwise "rendered unrecognizable" before being placed in a puncture-proof container labeled with the universal biohazard symbol. This precaution is intended to prevent drug addicts from reusing the needles as well as to protect the hospital environment from contamination by medical waste.
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L. Fleming Fallon, Jr., MD, DrPH