When to use IV Fluids – Study Notes

• IV fluids differ by:

  • Na⁺ concentration

  • Osmolality (isotonic, hypotonic, hypertonic)

  • pH

• Choice depends on: volume status, sodium level, and clinical scenario

1. Normal Saline (0.9% NaCl)

• Contents: Na⁺ 154, Cl⁻ 154

• Osmolality: Isotonic (~308)

• pH: Acidic (~5.7)

• Uses:

  • First-line resuscitation fluid (trauma, hypovolemia, sepsis)

  • Hyponatremia (but risk of overcorrection if chronic)

• Complications:

  • Large volumes → hyperchloremic metabolic acidosis

2. Half Normal Saline (0.45% NaCl)

• Contents: Na⁺ 77, Cl⁻ 77

• Osmolality: Hypotonic (~154)

• pH: ~5.7 (acidic)

• Uses:

  • Hypernatremia (↓ Na load)

• Complications:

  • Can worsen hyponatremia

  • Can cause cerebral edema if given too rapidly

3. D5W (5% Dextrose in Water)

• Contents: Glucose only (50 g/L)

• Osmolality: Slightly hypotonic (~252)

• pH: Acidic (~5)

• Uses:

  • Hypernatremia (dilutes Na, no sodium content)

  • Free water replacement

• Complications:

  • Hyperglycemia, cerebral edema in rapid correction

4. D5 ½ NS (D5W + 0.45% NaCl)

• Contents: Na⁺ 77, Cl⁻ 77, Glucose 50 g/L

• Osmolality: Hypertonic (~406)

• Uses:

  • Maintenance fluid (esp. NPO or peri-op patients)

  • Provides glucose + some electrolytes

• Complications:

  • Hyperglycemia

  • Not for rapid resuscitation

5. Lactated Ringer’s (LR)

• Contents: Na⁺ 130, Cl⁻ 109, K⁺ 4, Ca²⁺ 3, Lactate (buffer → HCO₃⁻)

• Osmolality: Isotonic (~273)

• pH: ~6.5 (closer to physiologic)

• Uses:

  • Resuscitation (esp. OR, trauma, sepsis)

  • Preferred over NS in large volumes (less acidosis risk)

• Complications:

  • Contains K⁺ → caution in renal failure

  • Contains Ca²⁺ → incompatible with some meds/blood transfusions

6. Plasma-Lyte

• Contents: Na⁺ 140, Cl⁻ 98, K⁺ 5, Mg²⁺ 3, Acetate & Gluconate (buffers)

• Osmolality: Isotonic (~294)

• pH: ~7.4 (closest to plasma)

• Uses:

  • Resuscitation (balanced solution, closest to ECF)

  • Alternative to LR

• Complications:

  • Cost/availability may limit use

Clinical Scenarios

• Hypovolemic shock / trauma: Start with NS → switch to LR/Plasma-Lyte if large volumes needed

• NPO/pre-op maintenance: D5 ½ NS (glucose + some electrolytes)

• Hyponatremia: NS or 3% hypertonic saline (depending on severity/acuity)

• Hypernatremia: D5W or ½ NS (↓ sodium load, free water replacement)

• Large-volume resuscitation (OR/ICU): LR or Plasma-Lyte (avoid NS-induced acidosis)

Key Complication to Remember:

• Too much NS → hyperchloremic metabolic acidosis

• Too rapid hyponatremia correction → osmotic demyelination (central pontine myelinolysis)

• Too rapid hypernatremia correction → cerebral edema