Electrolyte solutions: Milliequivalents,
millimoles and milliosmoles
Dr. Osama A. A. Ahmed
Milliequivalents, millimoles and milliosmoles
•
Milliequivalent (mEq) is used in the United states, while in the international system
Molar concentrations (mmol/L or mmol/L) are used throughout the world.
•
Under normal conditions blood plasma contains 154 mEq of cations and an equal
number of anions
•
Milliequivalent is the amount, in milligram, of a solute equal to 1/1000 of its gram
equivalent weight
mg  Valence
mEq 
Atomic, molecular or formula weight
mEq  Atomic, molecular or formula weight
mg 
Valence
Dr. Osama A. A. Ahmed
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Milliequivalents, millimoles and milliosmoles
• What is the concentration, in mg/ml, of a solution containing 2 mEq of
potassium chloride (KCl) per milliliter?
• M.Wt. of KCl = 74.5
• Equivalent weight of KCl = 74.5
1 mEq of KCl 
•
1
 74.5 g  0.0745 g  74.5 mg
1000
2 mEq of KCl = 74.5 X 2 = 149 mg/ml
• OR
mEq  Atomic, molecular or formula weight
mg 
Valence
•
Dr. Osama A. A. Ahmed
mg / ml 
2 (mEq / ml )  74.5
 149 mg / ml
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Milliequivalents, millimoles and milliosmoles
• What is the concentration, in g/ml, of a solution containing 4 mEq of calcium
chloride (CaCl2.2H2O) per milliliter?
• M.Wt. of CaCl2.2H2O = 147
• Equivalent weight of CaCl2.2H2O = 147/2 = 73.5
1 mEq of CaCl2 .2H 2 O 
•
1
 73.5 g  0.0735 g
1000
4 mEq of CaCl2.2H2O = 0.0735 g X 4 = 0.294 g/ml
• OR
mEq  Atomic, molecular or formula weight
mg 
Valence
•
mg / ml 
Dr. Osama A. A. Ahmed
4 (mEq / ml ) 147
294
 294 mg / ml 
 0.294 g / ml
2
1000
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Milliequivalents, millimoles and milliosmoles
•
Millimoles (mmol) used by SI to express electrolyte concentrations in millimoles per
liter (mmol/L).
•
For monovalent species, the numeric values of the milliequivalent and millimole are
identical
•
Millimole is the amount, in milligram, of a solute equal to 1/1000 of its gram
molecular weight. A mole is the molecular weight of a substance in grams.
•
•
Example
How many millimoles of monobasic sodium phosphate (m.w. 138) are present in 100 g
of the substance?
•
1 mole = 138 g
•
1 mole
138 g
•
X mole
100 g
•
How many milligrams would 1 mmol of monobasic sodium phosphate weigh?
•
1 mole = 138 g
Dr. Osama A. A. Ahmed
so
X = 0.725 mole = 725 mmol
1 mmol = 138 mg
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Milliequivalents, millimoles and milliosmoles
•
Osmolarity
•
U.S. Pharmacopeia states the knowledge of osmolar concentration of parenteral fluids
is essential.
•
This information indicates to the practitioner whether this solution is hypo-osmotic,
iso-osmotic or hyper-osmotic with regard to biologic fluids and membranes.
•
The unit used to measure osmotic concentration is the milliosmole (mOsmol)
•
Osmotic pressure is proportional to the total number of particles in solution.
•
For nonelectrolytes (e.g. dextrose), a 1 mmol represents 1 mOsmol
•
For electrolytes, the total number of particles in solution depends on the degree of
dissociation of the substance
1 mmol of NaCl (Na+ + Cl-) represnts 2 mOsmol, 1 mmol CaCl2 represents 3
mOsmol, and 1 mmol of sodium citrate (Na3 C6H5O7) represents 4 mOsmol (3 Na +
C6H5O7) of total particles.
•
mOsmol / L 
Dr. Osama A. A. Ahmed
Weight of subs tan ceg / L 
 Number of species 1000
Molecular Weight
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Milliequivalents, millimoles and milliosmoles
•
Example
•
Calculate the ideal osmolarity of 0.9 % NaCl injection?
9g/L
mOsmol / L 
 2 1000  308 mOsmol / L
58.5 g
•
Because of bonding forces, however, n is slightly less than 2 for solutions of sodium
chloride at this concentration, and the actual measured osmolarity is about 286
mOsml/L
•
A distinction should be madebetween the terms osmolarity and osmolality
•
Osmolarity is the milliosmoles of solute per liter of solution.
•
Osmolality is the milliosmoles of solute per kilogram of solvent.
•
Normal serum osmolality is considered within the range of 275 to 300 mOsmol/kg.
•
•
Osmometers are commercially available for use in the laboratory to measure osmolality
Abnormal blood osmolality can occur with shock, trauma, burns, electrolyte imbalance,
hyperglycemia or renal failure
Dr. Osama A. A. Ahmed
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Milliequivalents, millimoles and milliosmoles
•
Example: How many a) millimoles, b) milliequivalents, and c) milliosmols of
calcium chloride (CaCl2. 2H2O – m.w. 147) are represented in 147 ml of a 10 % w/v
calcium chloride solution?
•
10 g
100 ml
•
X
147
•
1 mmol = molecular weight in grams / 1000 = 147/1000 = 0.147 g = 147 mg
•
1 mmol
147 mg
•
X mmol
14700 mg
•
OR
mmol 
•
•
mOsmol / L 
X = 14700/147 = 100 mmol
mmol= 14700/147 = 100 mmol
= 14700 x 2/ 147 = 200
Weight of subs tan ceg / L 
 Number of species 1000
Molecular Weight  g 
mOsmol 
Dr. Osama A. A. Ahmed
mg
molecular weight
mg  Valence
Atomic, molecular or formula weight
mEq 
•
X = 147 x 10/100= 14.7 g = 14700 mg
Weight of subs tan cemg 
 Number of species
Molecular Weight
= 14700 X 3/147 = 300
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Clinical considerations of water and electrolyte balance
•
Water provides the environment in which cells live and is the primary medium for the
ingestion of nutrients and the excretion of metabolic waste products.
•
Maintaining body water and electrolyte balance is an essential component of good
health.
•
Fluid and electrolyte therapy (oral or parenteral) is provided either for maintenance
requirements or to replace serious losses or deficits.
•
Example, a patient taking diuretics may simply require a daily oral potassium
supplement along with adequate intake of water. Hospitalized patients commonly receive
parenteral therapy of fluids and electrolytes to support ordinary metabolic functions.
•
In adult males, total body water ranges between 55% and 65% of body weight depending
on the proportion of body fat. Adult women are about 10% less than adult men. New
born infants have approximately 75% body water.
•
About 66.7 % (2/3) of adult’s body water is intracellular and about 33.3 % (1/3) is
extracellular
•
1500 ml of water per square meter may be used to calculate the daily requirements for
adults.
•
On weight basis, 32 ml/kg for adults and 100-150 ml/kg for infants
Dr. Osama A. A. Ahmed
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Clinical considerations of water and electrolyte balance
•
Body fluids are extracellular (intravascular or interstitial) and intracellular (within
cells)
•
Osmolality of intracellular fluid and extracellular fluids is about equal (cell
membrane) this value is about 290 mOsm/kg water.
•
The plasma osmolality is approximated by the formula
plasma osmolality mOsm / kg   2Na  K  plasma 
BUN   Glu cos e
2.8
18
•
Where Na and K are in mEq/L, and blood urea nitrogen (BUN) and glucose
concentrations are in mg/100 ml (mg/dl)
•
Example, Estimate the plasma osmolality from the following data: sodium 135
mEq/L; blood urea nitrogen, 14 mg/dL; and glucose, 90 mg/dL
plasma osmolality mOsm / kg   2 135  4.5 
•
14 90

2.8 18
= 2 (139.5) + 5 + 5 = 289
Dr. Osama A. A. Ahmed
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