Measuring
11 Reading Syringes
Lesson
Learning Outcomes
By the end of this chapter, learners will be able to:
- identify the volume of liquid in a syringe, and
- select the most appropriate syringe to draw up a volume of liquid.
Syringe Units of Measure
Syringes come in a variety of sizes and are most often labelled for measurement in millilitres (mL) of liquid. It is possible you may see some syringes measuring cubic centimeters (cm3), but most large companies use only mL. 1 cm3 is equivalent to 1 mL. Insulin syringes, used only in drawing up insulin, measure units of insulin — not millilitres of insulin. Less commonly, you will see some syringes packaged with particular medications labelled in imperial units, such as teaspoons or tablespoons. For instance, a liquid antibiotic for pediatric patients may be packaged with a syringe measuring teaspoons of liquid.
Three samples of syringes with difference measurements are included below:
Reading Syringe Volumes
Attention to detail is required to read syringe volumes accurately.
- Identify the unit of measure for the syringe you are using.
- The barrel of the syringe is marked with graduated measurements of a particular unit of measure. Long or possibly bold lines mark whole units, with whole numbers often marked on the syringe barrel.
- Identify the size of graduated measurements.
- Depending on the total capacity of the syringe, the space between each line on syringes will vary in volume. For instance, in a 3 mL syringe, each space between lines is equal to 0.1 mL. In a 5 mL syringe, each space is equal to 0.2 mL.
- Identify where the end of the plunger is.
- The liquid inside the syringe will take up space up to the edge of the plunger inside the syringe. This edge is what should be compared to the graduated measurements to determine how much liquid is inside the syringe. The plunger inside the syringe is large and usually shows two sharp edges where the rubber is touching the inside of the syringe barrel. The edge you are looking at is always going to be the edge closed to the tip of the syringe, not the edge close to where your fingers are holding the flanges and plunger rod.
- Determine if the volume is accurate.
- If bubbles are present, the measurement of volume will not be accurate. Remove the bubbles before reading the volume of liquid.
- Determine the volume of liquid present.
- Now you are ready to read the volume of liquid in the syringe. Compare the edge of the plunger to the graduated markings to determine how much liquid is in the syringe.
Sample Exercise 11.1
Use the image below to answer the questions and click on “Answers” to check your work.
Questions:
- What is the capacity of the syringe?
- How much volume is between each graduated measure on the syringe?
- Identify the volume of liquid in the pictured syringe.
Answers:
- 5 mL
The capacity is the total volume the syringe can measure. This is represented by the largest number on the scale, and will be closest to the flange of the