Electrolyte solutions: Milliequivalents, millimoles and milliosmoles Dr. Osama A. A. Ahmed.
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Transcript of 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
,
Dr. Osama A. A. Ahmed 3
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
weightformulaormolecularAtomicmEqmg
,
mgggKClofmEq 5.740745.05.741000
11
mlmgmlmEq
mlmg /1491
5.74)/(2/
Dr. Osama A. A. Ahmed 4
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
weightformulaormolecularAtomicmEqmg
,
ggofmEq 0735.05.731000
1O.2HCaCl1 22
mlgmlmgmlmEq
mlmg /294.01000
294/294
2
147)/(4/
Dr. Osama A. A. Ahmed 5
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
Dr. Osama A. A. Ahmed 6
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
Dr. Osama A. A. Ahmed 7
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/
Dr. Osama A. A. Ahmed 8
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
Dr. Osama A. A. Ahmed 9
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 10
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