Normal
Normal saline (NS) is the commonly-used phrase for a solution of 0.90% w/v of NaCl, about 300 mOsm/L or 9.0 g per liter.a Less commonly, this solution is referred to as physiological saline or isotonic saline, neither of which is technically accurate. NS is used frequently in intravenous drips (IVs) for patients who cannot take fluids orally and have developed or are in danger of developing dehydration or hypovolemia. NS is typically the first fluid used when hypovolemia is severe enough to threaten the adequacy of blood circulation, and has long been believed to be the safest fluid to give quickly in large volumes. However, it is now known that rapid infusion of NS can cause metabolic acidosis.
The solution is 9 grams of sodium chloride (NaCl) dissolved in water, to a total volume of 1000 ml. As 1 grams NaCl occupies 0.18 level teaspoons, 9 grams NaCl is 1.62 level teaspoons. The mass of 1 millilitre of normal saline is 1.0046 gram at 22 °C. The molecular weight of sodium chloride is approximately 58.5 grams per mole, so 58.5 grams of sodium chloride equals 1 mole. Since normal saline contains 9 grams of NaCl, the concentration is 9 grams per liter divided by 58.5 grams per mole, or 0.154 mole per liter. Since NaCl dissociates into two ions – sodium and chloride – 1 molar NaCl is 2 osmolar. Thus, NS contains 154 mEq/L of Na+ and Cl−. It has a slightly higher degree of osmolarity (i.e. more solute per litre) than blood (However, if you take into account the osmotic coefficient, a correction for non-ideal solutions, then the saline solution is much closer to isotonic. Osmotic coefficient of NaCl is about 0.93; therefore 0.154 × 1000 × 2 × .93 = 290.) Nonetheless, the osmolarity of normal saline is a close approximation to the osmolarity of NaCl in blood.
One litre of 0.9% Saline contains:
- 154 mEq of sodium ion = 154 mmol/L
- 154 mEq of chloride ion = 154 mmol/L
Read more about this topic: Saline (medicine), Concentrations
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