Normal Saline (0.9% NaCl): Composition, Properties, and Medical Uses

Normal saline (NS) is a sterile aqueous solution of 0.9% sodium chloride (NaCl) (154 mEq/L Na⁺, 154 mEq/L Cl⁻). Its osmolarity (~308 mOsm/L) matches human plasma, making it isotonic.

Chemical Composition

• NaCl: 9 g/L
• Water for injection: q.s. 1 L
• pH: 4.5–7.0 (typically ~5.5 due to dissolved CO₂); no buffer.

Key Properties

• Isotonic: No net water shift across cell membranes → minimal cellular edema or shrinkage.
• Electrolyte Content: Na⁺ and Cl⁻ only; no K⁺, Ca²⁺, Mg²⁺, bicarbonate, or lactate.
• Chloride Load: High Cl⁻ (154 mEq/L vs. plasma 100–106) → risk of hyperchloremic metabolic acidosis with large volumes.
• Compatibility: Compatible with most IV drugs; check specific compatibility charts.

Common Medical Uses

• IV Fluid Resuscitation: Initial bolus for hypovolemia, sepsis, shock.
• Maintenance Fluids: With added KCl, dextrose.
• Wound Irrigation: Mechanical cleansing; isotonicity minimizes tissue trauma.
• Nebulization: Vehicle for bronchodilators, hypertonic saline for cystic fibrosis/bronchiolitis.
• Device Flushing: IV lines, catheters, ports.
• Diluent: For IV push medications.

Limitations & Alternatives

• Large-volume resuscitation → balanced crystalloids (Plasma-Lyte, Ringer’s Lactate) preferred to avoid hyperchloremia.
• Not for maintenance alone (no K⁺, calories, buffer).
• Contraindicated in severe hypernatremia or hyperchloremic acidosis.

Normal saline remains a versatile, inexpensive, and widely available crystalloid, but balanced solutions are increasingly favored for high-volume resuscitation.