A practical nursing student needs to be equipped with the proper knowledge and skills to make accurate dosage calculations necessary for health care. There is usually a section in the NCLEX-RN examination testing every student on their ability to calculate dosages involved in a medical administration setup.
Every aspiring nurse should accurately demonstrate an understanding of critical clinical situations requiring comprehensive thinking and dosages analysis.
The three measurement systems in pharmacology
1. Household: Nurses use this system when calculating dosages for home-care patients: The common household unit of measurements includes:
· 1 teaspoon = 5 mL
· 1 tablespoon = 3 teaspoons
· 1 ounce (fluid) = 2 tablespoons
· 1 ounce (weight) = 30 g
· 1 cup = 8 ounces
· 1 pint = 2 cups
· 1 quart = 2 pints
· 1 gallon = 4 quarts
· 1 pound – 16 ounces
2. Metric: The length, volume and weight measurement involved in this system include:
· 1 millimeter = 0.001 meter
· 1 centimeter = 0.01 meter
· 1 decimeter = 0.1 meter
· 1 kilometer = 1000 meters
3. Apothecary: Examples of measurements in this system include:
· 1 grain of wheat = 60 mg
· 1 scruple = 20 grains
· 1 dram = 3 scruple
· 1 ounce = 8 drams
· 1 pound = 12 ounces
It is essential to be aware of the different measurement systems and the conversions appropriate among them. Accuracy is a priority when administering medication as a nurse; therefore, memorizing conversion factors and looking them up when unsure is paramount.
What are fractions?
There are two types of fractions:
- Proper fractions = lesser than one
- Improper fractions = more than 1
The correct way to write fractions.
The top digit is called the numerator, while the bottom is the denominator: x/y
Simplifying fractions involves reducing them to the lowest common denominator. This mathematical solution divides the numerator and the denominator evenly until no number can evenly divide both numerals. An example of a calculation to demonstrate this concept includes: 24/50 = 12/25
What are mixed numericals?
These figures contain a fraction and a whole number that is greater than one. Converting mixed digits to fractions makes them more straightforward to work with: The steps to take during this process are:
- Multiply the whole number with the fraction’s denominator, then sum up the result with the numerator.
- Write a fraction that includes the answer as the numerator but maintains the previous denominator value of the mixed number.
- A calculation example of a mixed number to improper fraction conversion includes: 5 2/3 = (5 x 3 +2) / 5 = 17 /3
What are decimals?
These expressions include a whole number, a number after a decimal symbol that is usually not more than one. A dot is the point that separates the two representations. The number that immediately follows the dot is in the tenths positions, next is the hundredth, then thousandths.
Any numerical with a decimal and a zero acting as the whole number before the dot makes the whole expression less than one. It is appropriate to round off any decimals in pharmacology calculations.
When rounding off to the nearest whole number, evaluate the number following the symbol in the tenths position. If it is more significant than five, add one to the number preceding the decimal. To round off to the nearest tenths, look at the value in the hundredths position and if it is lower than five, leave the number as it is.
Examples of decimal numbers:
· Rounded off to the nearest whole number
2.6 = 2
5.3 = 5
· Rounded off to the nearest tenths
7.10 = 7.1
5.97 = 6.0
· Rounded off to the nearest hundredths
3.769 = 3.77
Ratio and proportions in dosage calculations
A ratio is a way to compare the size, weight, or volume of a group of two or more numbers: The different ratio representations include:
- x to y
Ratios and proportions are a critical part of dosage calculations in nursing. As a nursing student, you should be aware of the specific processes involved when calculating:
- Oral medication dosages
- Intramuscular and subcutaneous medications
- Intravenous flow rates
To understand how you can critically apply your knowledge and skills to make error-free and safe calculations for patients, check out this free course on dosage calculations.