General Critical Care

Among the following IV solutions — D5 ½ NS, Albumin, Normal Saline (NS), and Lactated Ringer (LR) — the one with the highest osmolality is D5 ½ NS.

🔎 Here’s why:

• Osmolality reflects the number of dissolved particles in a solution.

• For electrolytes (Na⁺, K⁺, Cl⁻, lactate), mEq/L ≈ mOsm/L.

Therefore:

• Normal Saline (0.9% NaCl): 154 Na⁺ + 154 Cl⁻ = 308 mOsm/L

• Lactated Ringer: 130 Na⁺ + 4 K⁺ + 2.7 Ca²⁺ + 109 Cl⁻ + 28 lactate = 273.7 mOsm/L

• 5% Albumin: ≈ 330 mOsm/L (varies by manufacturer)

• D5 (5% dextrose):

  • Contains 50 g/L (50,000 mg/L) of dextrose.

  • Molecular weight of dextrose = 180 g/mole.

  • 50,000 ÷ 180 = 278 mOsm/L.

• D5 ½ NS (5% dextrose + 0.45% NaCl): 278 (dextrose) + 77 Na⁺ + 77 Cl⁻ = 432 mOsm/L