Units of Measure Math for Clinical Practice
Volume
• 1 liter = L
• 1 milliliter = mL or cc
(cc is not to be used anymore according to JACOH standards but it is a common error since it has been used for years)
CC = mL
Ounces to mL
• You are doing intake and output and the mother states the infant has consumed 3 ½ ounces of formula. How many mL has the infant consumed?
• 3.5 x 30 mL = 105 mL
• You would record 105 mL on the intake record
Tablespoons
• You are teaching a geriatric patient how to measure her medications. She is to take 15 mL of liquid Maalox to aid digestion.
• You would instruct her to use what household measuring device to take her mediation?
• Teaspoon or tablespoon • She would take one tablespoon of
medication.
Teaspoon
• You are working with a mother of a toddler and she has been instructed to give the child 1 ½ teaspoons of medication. You are demonstrating how to give the medication with a syringe with measurements in mL.
• How many mL would you have her give?
1 Teaspoon = 5 ml
• 1 ½ teaspoons = 1.5 teaspoons
• 1.5 teaspoon x 5 mL = 7.5 mL
• You would have her draw up 7.5 mL in a po syringe.
Nursing Alert
• Remember if there is not a number to the left of the decimal point a zero is placed there to highlight the decimal point placement.
• Correct: 0.5 mL or 0.25 g
• Incorrect: 5.0 mL or 25.0 g
Nursing Alert
• Decide whether you are converting from smaller unit to larger unit or larger unit to smaller unit.
Liter to milliliters
• 1 liter (L) = 1000 milliliters (mL)
• 1.2 L = ___________
• 1.2 x 1000 = 1200 mL
Milliliters (mL) to Liters (L)
• Change mL to Liter (L)
• mL is smaller than a liter
• Move decimal point three places to the right
• 750 mL = 0.75 L
Metric Units Weight
• Kilogram = kg
• 1 kg = 1000 grams (g)
• 1 gram (g) = 1000 milligrams (mg)
• 1 milligram (mg) = 1000 micrograms mcg
How to calculate kilograms
• Remember you will weigh less in kilograms
• To convert pounds to kilogram you divide by 2.2
• Convert 100 pounds to kg
• 100 / 2.2 = 45.454 or 45.45
• In the infant / small child carry out to the 100th or two decimal places.
Example
• Convert the following metric measurement:
• 0.2 mg = ______ g.
• (gram is larger than a mg)
• Need to move the decimal 3 places or divide by 1000.
• Answer 0.2 mg = 0.0002 g
Example
• 100 mcg = ______ mg
• You are going from a smaller unit to a larger unit.
• You would move the decimal point 3 places or divide by 1000.
• 100 mcg = 0.1 mg
International Units
• Heparin, insulin, penicillin, epoetin products (Epogen, Procrit) are measured in international units.
• Example: regular insulin 10 units SQ in am
• Example: penicillin 600,000 units IM x one dose
Milliequivalent Measures
• Do not confuse with milligrams.
• Notation is mEq
• Milliequivalent measures the number of grams of equivalent weight of a drug contained in 1 mL of normal saline.
mEq
• Common drugs: sodium bicarbonate, sodium chloride, potassium chloride.
• Examples:
• 10 mEq of potassium chloride to ½ L of IV solution
• 15 mEq of sodium chloride to 1 L of IV solution
Conversions
• Clinical connection: often you need to calculate between different systems of measure.
Practice Problems
• gr ¾ = ___________ mg
• gr ¼ = ___________ mg
• gr 15 = ___________ mg
• 300 mg = _________ gr
• 60 mg = __________ gr
• 30 mg = __________ gr
• gr 1/6 = ___________ mg
Practice problems
• The bottle of Tylenol states that you are to give X (ten grains) of Tylenol.
• How many mgs are you giving ________
Ratio – Proportion Method
• Using the ratio proportion method offers a systematic approach to solving clinical math calculations.
The Set-up
• Solving the unknown
• The cookies and the eggs
• If the recipe states you need 2 eggs to make 2 dozen cookies. How many eggs do you need to make a dozen cookies?
• 24 cookies 12 cookies
• 2 eggs = x eggs
Practice Problem
• Page 106
• Lorazepram 3 mg IV every 6 hours as needed.
• Lorazepam is supplied as 4 mg / mL
The set-up
• 4 mg3 mg
• 1mL = x mL
• (cross multiply)
• 3 / 4 x = 0.75 mL
• You would draw up 0.75 mL to equal 2 mg of Lorazepam
Practice Problem
• Page 108
• Phenytoin sodium 300 mg by mouth at bedtime.
• Phenytoin sodium supplied as 125 mg / 5 mL.
The Set-up
• 125 mg 300 mg
5 mL = x mL
(Cross multiple) (X is on the bottom)
1500
125 X = 12 mL equals 300 mg of the drug
Determine the dosage
• 5 mcg / kg / day
• 5 mcg x 79.09 (weight in kg) = 395.45 mcg per dose
• Drug is rounded to 395 mcg per dose to be added to 50 mL of Dextrose 5% in Water.
Practice Problem
• Phenobarbital 30 – 120 mg / kg per day in 3 divided doses
• Physician orders the maximum dose or 120 mg / day to be given q 8 hours.
• 1st you would need to divide 120 mg by 3 doses = 40 mg per dose