Calculations Flashcards
How many grams is 1 oz?
28.4 g
How many grams is 1 lb?
454 g
How much does 1 grain (gr) weigh?
65 mg (approx) 64.8 mg (actual)
how many mmol does 1 mEq of K+, Na+, and other monovalent ions??
1 mmol
How many mmol does 1 mEq of Ca++ and other divalent ions?
0.5 mmol
Aminophylline and theophylline conversion
amino –> theo; multiply by 0.8
theo –> amino; divide by 0.8
ratio strength
one unit of solute contained in the total amount of a solution (1:500)
PPM to percentage
Move decimal left 4 places
Percentage to PPM
Move decimal right 4 places
Specific gravity (SG)
the ratio of the density of a substance to the density of water
weight of substance/weight of water
SG > 1 = substance heavier than water
SG < 1 = substance lighter than water
SG = g/mL16
Ratio strength to percentage
100/ ratio strength
Percentage to ratio strength
100/% strength
Osmolarity
the number of particles per liter of solution
Dissocation of particles
The number of particles of a particular compound when in solution
Ex:
# of dissociation particles of dextrose = 1
# of dissociation particles of NS = 2 (breaks down into Na+ and Cl-)
Dissociation of KCl
2
Dissociation of Sodium acetate
2
Dissociation of Calcium chloride (CaCl2)
3
Dissociation of sodium citrate (Na3C6H5O7)
4
Osmolarity equation
mOsm/L = wt of substance (g/L)/molecular weight (g/mole) X # of particles X 1000
Tonicity
describes osmolarity in context of body fluids
Dissociation factor (i)
percentage that dissociates into ions
Ex:
i = 1.8 means 80% of compound will dissociate
i = 1 means 0% will dissociate
Dissociation factor
1 ion = 1
2 ions = 1.8
3 ions = 2.6
continue to add 0.8 for each ion
E value
The amount of drug that produces a certain osmolarity and the amount of NaCl that produces the same osmolarity
E value equation
E = 58.5 x diss. factor / MW of drug x 1.8
1 gallon = ____ mL
3785 mL
Molecular weight of NaCl
58.5
What is a mole?
grams/MW
mmol = mg/MW
For all species, the numeric value of mEq is equal to mmol (t/f)
False
only monovalent species
Milliequivalents formula
mEq = (mg x valence) / MW
BMI formula
kg/m^2
BMI classifcations
< 18.5: underweight
18.5-24.9: Normal weight
25-29.9: Overweight
>30: Obese
Normal wasit circumference
women: 35 inch or less
Men: 40 inch or less
What value usually indicates dehydration?
BUN;SCr ration > 20:1
both lab values will increase during dehydration
What weight should be used when calculating CrCL?
Underweight (TBW < IBW): use TBW
Noraml weight (BMI <25): use IBW
Overweight: Use ABW
What drug class do you use ABW in obese patients?
Aminoglycosides
What body weight would you use for dosing LMWH, UFH, vanco in obese pts
usually TBW
