18.2 Basic Concepts
Syringes
Syringes are used to administer parenteral medications. A disposable syringe is a sterile device that is available in various sizes ranging from 0.5 mL to 60 mL. A syringe consists of a plunger, a barrel, and a needle hub. Syringes may be supplied individually or with a needle and protective cover attached. See Figure 18.1[1] for an illustration of the parts of a syringe.
Luer lock syringes have threads in the needle hub that provide a secure connection of needles, tubing, or other devices. See Figure 18.2[2] for an image of a Luer lock syringe with a barrel and a readable scale. This image shows a syringe that holds 12 cc, also referred to as 12 mL. When withdrawing medication, match up the top of the plunger and the line on the barrel scale with the amount of medication you need to administer. In this image, 3 mL of medication is contained in the syringe. Luer slip (or Slip Tip) syringes allow a needle to be quickly and conveniently pushed straight on to the end of the tip (if a needle is required). Luer slip syringes are common in Foley catheterization kits.
View a supplementary YouTube video on How to Read a Syringe[3]
Insulin is administered using a specific insulin syringe. Insulin syringes are marked in units, not milliliters (mL), because insulin is prescribed by providers in units, not mLs. Insulin syringes are available in two different sizes, one of which can hold 50 units and one which can hold 100 units. A regular syringe marked in milliliters should never be used to administer insulin. All insulin syringes have orange caps for quick identification, but verify the markings are in units to prevent a medication error. See Figure 18.3[4] for an image of a 50-unit insulin syringe with a white safety shield attached.
Needles
Needles are made out of stainless steel. They are sterile and disposable and are available in various lengths and sizes. A needle is made up of the hub, shaft, and bevel. The hub fits onto the tip of the syringe. All three parts must remain sterile at all times. The bevel is the tip of the needle that is slanted to create a slit into the skin. See Figure 18.4[5] for an image of a bevel.
Gauge and Length
The gauge of a needle refers to its diameter. Needles range in various sized gauges from small diameter (25 to 29 gauge) to large diameter (18 to 22 gauge). Note that the larger the diameter of a needle, the smaller the gauge number. Larger diameter needles (18-22 gauge) are typically used to administer thicker medications or blood products. See Figure 18.5[6] for an image comparing various needle lengths and gauges. Read more about needle gauges according to type of injection in Table 18.2 in the “Anatomic Location” subsection.
Gauge and length are marked on the outer packaging of needles. Needle length varies from 1/8 inches to 3 inches and is selected based on the type of injection. Nurses select the appropriate gauge and length according to the medication ordered, the anatomical locatio