Sodium Content in 0.9% Saline
0.9% saline contains 154 milligrams of elemental sodium per milliliter.
Calculation and Composition
0.9% saline (w/v) means 0.9 grams of sodium chloride per 100 mL, which equals 9 grams per liter or 9 mg per mL of NaCl 1
Sodium chloride has a molecular weight of 58.5 g/mol, with sodium contributing 23 g/mol (approximately 39.3% of the total molecular weight) 1
Therefore, each milliliter of 0.9% saline contains: 9 mg NaCl × 0.393 = 3.54 mg of elemental sodium per mL 1
Expressed in milliequivalents: 0.9% saline contains 154 mEq/L of sodium, which equals 0.154 mEq/mL 2, 3
Since 1 mEq of sodium = 23 mg, this translates to 0.154 mEq/mL × 23 mg/mEq = 3.54 mg of elemental sodium per mL 2
Clinical Context
Normal saline has an osmolarity of 308 mOsm/L, making it truly isotonic compared to plasma (275–295 mOsm/L) 3
The 154 mEq/L concentration of both sodium and chloride in 0.9% saline represents a non-physiological 1:1 ratio that differs significantly from plasma, where the normal chloride concentration is approximately 95–105 mEq/L 4, 5
This supraphysiologic chloride content can cause hyperchloremic metabolic acidosis when administered in large volumes (>1–1.5 L), which is why balanced crystalloids like Ringer's lactate are now preferred for most resuscitation scenarios 4, 5