Electrolyte solutions: Milliequivalents, millimoles and milliosmoles Dr. Osama A. A. Ahmed.

Electrolyte solutions: Milliequivalents, millimoles and

milliosmolesDr. Osama A. A. Ahmed

Dr. Osama A. A. Ahmed 2

Milliequivalents, millimoles and milliosmoles• Milliequivalent (mEq) is used in the United states, while in the international system

Molar concentrations (mmol/L or mol/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

weightformulaormolecularAtomic

ValencemgmEq

,

Valence

weightformulaormolecularAtomicmEqmg

,


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

• 2 mEq of KCl = 74.5 X 2 = 149 mg/ml

• OR

•

Valence


,

mgggKClofmEq 5.740745.05.741000

11

mlmgmlmEq

mlmg /1491

5.74)/(2/


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

• 4 mEq of CaCl2.2H2O = 0.0735 g X 4 = 0.294 g/ml

• OR

•

Valence


,

ggofmEq 0735.05.731000

1O.2HCaCl1 22

mlgmlmgmlmEq

mlmg /294.01000

294/294

2

147)/(4/


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 X = 0.725 mole = 725 mmol

• How many milligrams would 1 mmol of monobasic sodium phosphate weigh?

• 1 mole = 138 g so 1 mmol = 138 mg


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.

1000

/tan/ speciesofNumber

WeightMolecular

LgcesubsofWeightLmOsmol


Milliequivalents, millimoles and milliosmoles• Example

• Calculate the ideal osmolarity of 0.9 % NaCl injection?

• 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

LmOsmolg

LgLmOsmol /30810002

5.58

/9/


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 X = 147 x 10/100= 14.7 g = 14700 mg

• 1 mmol = molecular weight in grams / 1000 = 147/1000 = 0.147 g = 147 mg

• 1 mmol 147 mg

• X mmol 14700 mg X = 14700/147 = 100 mmol

• OR mmol= 14700/147 = 100 mmol

• = 14700 x 2/ 147 = 200

•

• = 14700 X 3/147 = 300

weightformulaormolecularAtomic

ValencemgmEq

,

weightmolecular

mgmmol

1000

/tan/ speciesofNumber

gWeightMolecular

LgcesubsofWeightLmOsmol

speciesofNumber

WeightMolecular

mgcesubsofWeightmOsmol

tan


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


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

• 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

• = 2 (139.5) + 5 + 5 = 289

18

cos

8.22/

eGluBUNplasmaKNakgmOsmosmolalityplasma

18

90

8.2

145.41352/ kgmOsmosmolalityplasma

Electrolyte solutions: Milliequivalents, millimoles and milliosmoles Dr. Osama A. A. Ahmed.

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