# Electrolyte solutions: Milliequivalents, millimoles and milliosmoles

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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 Dr. Osama A. A. Ahmed

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 Dr. Osama A. A. Ahmed

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 = g X 4 = g/ml OR Dr. Osama A. A. Ahmed

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 g X mole g X = mole = 725 mmol How many milligrams would 1 mmol of monobasic sodium phosphate weigh? 1 mole = 138 g so mmol = 138 mg Dr. Osama A. A. Ahmed

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. Dr. Osama A. A. Ahmed

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 Dr. Osama A. A. Ahmed

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 ml X X = 147 x 10/100= 14.7 g = mg 1 mmol = molecular weight in grams / 1000 = 147/1000 = g = 147 mg 1 mmol mg X mmol mg X = /147 = 100 mmol OR mmol= 14700/147 = 100 mmol = x 2/ 147 = 200 = X 3/147 = 300 Dr. Osama A. A. Ahmed

Clinical considerations of water and electrolyte balance