After infusing 2 liters of isotonic (0.9%) saline rapidly, which body fluid compartment change is expected?

• A Equal distribution between ECF and ICF (1 liter each)
• B Predominantly ICF expansion with minimal ECF expansion
• C Predominantly ECF expansion (virtually all 2 L remains in ECF) with no change in ICF ✓
• D Transient ECF expansion followed by equal redistribution to ICF within 30 minutes

Explanation

Isotonic saline has the same osmolarity as plasma (~308 mOsm/L). When infused, it expands the ECF without changing plasma osmolarity; therefore no osmotic gradient is created to drive water into or out of cells. All of the infused volume remains in the extracellular compartment (distributed between intravascular and interstitial in a 1:3 ratio approximately). ICF volume remains unchanged. This is in contrast to hypotonic solutions (expand both ECF and ICF) or hypertonic solutions (expand ECF, shrink ICF).

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.