Practical Calculations Flashcards
AD
AS
AU
Right ear
Left ear
Both ears, each ear
ad lib
As much as desired
gt
gtt
Drop
Drops
mEq
milliequivalent
OD
OS
OU
Right eye
Left eye
Both eye, each eye
3 systems of measurement
- Metric
- Apothecary
- Household
Fundamental units of measurement in the metric system (weight, volume, length)
Gram
Liter
Meter
Units of measure for the biological sciences
Metric System
Base (gram, liter, meter) 1
Kilo 1000
Deci 1/10
Centi 1/100
Milli 1/1000
Micro 1/1,000,000
Nano 1/1,000,000,000
Pico 1/1,000,000,000,000
Convert 3000 mg to grams
3000 mg
3000 mg x 1 g
1000 mg
Cancel the mg
1 / 1000 = 0.001
0.001 x 3000 = 3
Stair step method - converting metric units
Divide by 10 each step up (move decimal one place to the left)
Multiply by 10 each step down (move decimal one place to the right)
Apothecary System
Minim italics m or min
Dram italics dr
Ounce italics oz
Grain italics gr
minim =
1 drop
Always expressed as a whole number
1 fluid dram =
4 ml
1 oz =
30 ml
1 grain =
64.8 (65) mg
Household system
Drop / gtt
Tablespoon / tbsp
Teaspoon / tsp
1 Tbsp =
15 ml
1 tsp =
5 ml
1 oz =
30 ml
Solvent
Solution capable of dissolving other substances
Solute
Substance that is dissolved in a liquid (solution)
Miscible / immiscible
Substances that form solutions /
Those that do not
Saturated
Containing the maximum amount of solute at a particular temperature and pressure
Suspension
Mixes of substances in which the solute is made up of very large particles
The strength of a mixture is expressed as a parts ratio or
Ratio concentration
A 1:32 dilution means
1 part drug to 31 parts solvent to make 32 parts total
Parts per million (ppm) =
1 mg of a solute in a kg or liter of solvent
Or
1 mcg of solute in a gram or ml
Parts per billion (ppb)
1 mcg in a kg or liter
1 nanogram in a gram or ml
1:32 as a percent concentration
1:32 = Y:100
1 = Y
32 100
32Y = 100
32 32
Y = 3.1%
How can concentrations be expressed
Parts ratio
Liquids - rate per volume
Liquids - volume per volume
Solids - weight per weight
Percent concentration
Parts of a solute per 100 parts of the solution
Percent w/v = grams of solute in 100 ml solution
Percent w/w = grams of solute in 100 g of diluent
Percent v/v = ml of solute in 100 ml solution
Convert a % solution to mg/ml
5% Lasix solution = x mg/ml
Multiply the % x 10
50 mg/ml
Convert a solution in mg/ml to a %
50 mg/ml lasix = x%
Divide the mg/ml by 10
50 / 10 = 5%
Mg% meaning
Number of mg in 100 ml of solution
Or
mg per deciliter (100 ml)
100% solution (w/w) =
5% solution =
100 g solute in 100 g solvent
5 g in 100 g solution
5 g + 95 g
100% solution v/v =
10% solution =
Pure drug/chemical
10 ml chemical in 100 ml solution
Diluting up aka
qs or quantity sufficient
How many grams of sodium chloride are needed to make 1 L of 0.9% sodium chloride?
Total volume of final drug solution x concentration = amount
grams needed = 0.9 x 1000 ml
100
9 grams
What percentage is a solution that contains 9 g of sodium chloride?
Percent solution = grams of solute x 100
Volume of solution
9 x 100 = 900
1000 1000 0.9%
What formula would be used to change the concentration (dilute) a solution?
V1 x C1 = V2 x C2
What you have on hand = what you want to make
V1 volume of stock solution/amount to use to prepare new volume
C1 original concentration of stock solution
V2 desired final volume
C2 desired final concentration
How would you prepare 100 ml of a 5% dextrose solution from a 50% dextrose solution?
V1 x 50% = 100 ml x 5%
V1 x 50 = 500 ml
V1 = 10 ml
When would you use milliequivalents?
When electrolytes are involved
An equivalent weight =
1 g molecular weight divided by the total positive valence of the material in question.
The concentration of an electrolyte solution is expressed as
mEq/L
Standard drip set vs micro drip. How many drops/ml?
15
60
Formula to calculate fluid drip rates
Volume of infusion (ml) x drop factor (gtt/ml)
Time of infusion (min)
= drops per min
CRI
Constant rate infusions
