Sodium Concentration in Normal Saline
Normal saline (0.9% sodium chloride) contains 154 mEq/L of sodium and 154 mEq/L of chloride, with an osmolarity of 308 mOsm/L. 1
Composition Details
- Sodium concentration: 154 mmol/L (or 154 mEq/L) 1
- Chloride concentration: 154 mmol/L (or 154 mEq/L) 1
- Total osmolarity: 308 mOsm/L 1
- pH: Slightly acidic (approximately 5.5) 1
Clinical Context
Normal saline is referred to as "isotonic saline" or "0.9% NaCl" in clinical practice, though it is technically slightly hyperosmolar compared to plasma. 1 The term "normal" is historical and does not reflect physiological sodium concentrations in plasma, which are typically 135-145 mEq/L. 1
Comparison to Other Common IV Fluids
- Half-normal saline (0.45% NaCl): 77 mEq/L sodium 1
- Ringer's lactate: 130 mmol/L sodium 1
- Plasma-Lyte: Similar to Ringer's lactate with physiologic sodium levels 2
- 3% hypertonic saline: 513 mmol/L sodium 1
- 7.5% hypertonic saline: 1283 mmol/L sodium 1
Important Clinical Caveat
The equal concentration of sodium and chloride (both 154 mEq/L) in normal saline is non-physiological and can cause hyperchloremic metabolic acidosis when administered in large volumes. 2, 3 This is because plasma chloride is normally 95-105 mEq/L, significantly lower than the 154 mEq/L in normal saline. 2
For large-volume resuscitation or prolonged fluid therapy, balanced crystalloid solutions (such as Lactated Ringer's or Plasma-Lyte) are increasingly preferred over normal saline to avoid chloride overload and associated complications including acute kidney injury. 1, 2, 4