Intravascular Volume Expansion: D5W vs 0.45% NaCl
0.45% NaCl provides superior intravascular volume expansion compared to D5W, though both are inferior to isotonic solutions like 0.9% NaCl for this purpose.
Physiological Distribution and Volume Expansion Capacity
Hypotonic solutions like D5W and 0.45% NaCl distribute primarily into intracellular and interstitial spaces rather than remaining intravascular, making them poor choices for volume expansion. 1
D5W (Dextrose 5% in Water)
- After glucose metabolism, D5W becomes free water that distributes across all body compartments 1
- Only approximately 8-10% remains in the intravascular space at equilibrium
- May actually worsen cerebral edema in acute neurological conditions by distributing into intracellular spaces 1
- Provides essentially no sustained intravascular volume expansion
0.45% NaCl (Half-Normal Saline)
- A substantial proportion distributes into intracellular spaces, limiting intravascular retention 1
- Approximately 25-30% remains intravascular at equilibrium
- Provides modest but inadequate volume expansion compared to isotonic solutions 1
- Has specific clinical indications in hyperglycemic crises when corrected sodium is normal or elevated 1, 2
Clinical Context for Appropriate Use
When 0.45% NaCl is Indicated
In diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS), 0.45% NaCl at 4-14 ml/kg/h is appropriate when corrected serum sodium is normal or elevated 1, 2:
- Calculate corrected sodium: Measured Na + 1.6 × ([Glucose - 100]/100) 2
- If corrected sodium is low, use 0.9% NaCl instead 1
- Ensure osmolality changes do not exceed 3 mOsm/kg/h 1, 3
When Neither Should Be Used
For true intravascular volume expansion in most clinical scenarios, isotonic crystalloids (0.9% NaCl or balanced solutions like Lactated Ringer's) are strongly preferred 1:
- Isotonic solutions distribute more evenly into extracellular spaces (interstitial and intravascular) 1
- Balanced crystalloids may reduce mortality and adverse renal events compared to 0.9% NaCl in hemorrhagic shock 1
- In acute ischemic stroke, isotonic solutions prevent exacerbation of cerebral edema 1
Critical Pitfalls to Avoid
- Never use D5W for volume resuscitation - it provides no meaningful intravascular expansion and may worsen cerebral edema 1
- Do not use 0.45% NaCl as first-line volume expansion except in specific hyperglycemic crisis scenarios with normal/elevated corrected sodium 1
- Failing to calculate corrected sodium in hyperglycemic patients leads to inappropriate fluid selection 3, 2
- In pediatric DKA, initial volume expansion must use 0.9% NaCl at 10-20 ml/kg/h to prevent cerebral edema, not hypotonic solutions 1
Direct Comparison Summary
Between these two options, 0.45% NaCl provides marginally better intravascular volume expansion than D5W, but both are fundamentally inadequate for this purpose. The clinical question itself suggests a need for volume expansion, which mandates isotonic crystalloid solutions in nearly all circumstances 1.