Volume Contribution of 1 L D5W
1 liter of D5W (5% dextrose in water) adds essentially 1 liter of free water to the body, as the dextrose is rapidly metabolized, leaving behind hypotonic fluid that distributes across all body compartments.
Physiologic Basis
- D5W is isotonic when infused (approximately 278 mOsm/L) but becomes hypotonic once the dextrose is metabolized by cells 1
- The solution contains no sodium or other electrolytes, meaning it provides no renal osmotic load once dextrose is cleared 1
- After dextrose metabolism, the remaining free water distributes across intracellular (2/3) and extracellular (1/3) compartments according to normal body water distribution 1
Clinical Volume Effects
- Plasma volume expansion: Approximately 80-100 mL per liter of D5W infused, as most water shifts intracellularly 1
- This contrasts sharply with isotonic crystalloids (0.9% saline), which expand plasma volume by approximately 300 mL per liter administered 1
- The minimal plasma volume expansion makes D5W inappropriate for resuscitation or volume replacement in hypovolemic states 1
Critical Distinction from Sodium-Containing Fluids
- Isotonic saline (0.9% NaCl) has a tonicity of
300 mOsm/kg H₂O, which exceeds typical urine osmolality in conditions like nephrogenic diabetes insipidus (100 mOsm/kg H₂O) by 3-fold 1 - Consequently, approximately 3 liters of urine are needed to excrete the renal osmotic load from 1 liter of isotonic saline, risking serious hypernatremia in patients unable to concentrate urine 1
- D5W delivers zero renal osmotic load after dextrose metabolism, making it the preferred fluid for hypernatremic states and conditions with impaired urinary concentration 1
Specific Clinical Applications
Hypernatremia Management
- D5W is the fluid of choice for hypernatremic dehydration, particularly in nephrogenic diabetes insipidus 1
- Salt-containing solutions should be avoided as their osmotic load exceeds urine osmolality and worsens hypernatremia 1
- Initial infusion rates of 100 mL/hour in adults provide slow, controlled correction of plasma osmolality 2, 3
Hypervolemic Hypernatremia
- Treatment requires achieving negative sodium/potassium balance exceeding negative water balance 4
- D5W combined with furosemide accomplishes this by providing free water while promoting sodium excretion 4
- Parenteral D5W decreases serum sodium by approximately 2.25 mEq/L per liter infused in ICU patients 5
Drug Dilution Context
- When D5W serves as a vehicle for medication infusions (epinephrine 1 mg in 250 mL D5W, dopamine 400 mg in 500 mL D5W), the volume contribution remains 1:1, but infusion rates are dictated by medication dosing rather than volume needs 1, 6
- Blood glucose monitoring is essential regardless of infusion rate when D5W is used as a drug vehicle 6
Important Caveats
- Avoid D5W in closed head trauma or elevated intracranial pressure: hypotonic fluid worsens cerebral edema by decreasing brain tissue specific gravity 7
- Hyperglycemia risk: 500 mL of D5W causes plasma glucose >10 mmol/L in 72% of non-diabetic surgical patients 8
- Cardiac/renal compromise: limit rates to ≤100 mL/hour and monitor closely for fluid overload despite minimal plasma expansion 2, 3
- In continuous renal replacement therapy, D5W can be infused prefilter to prevent overcorrection of hyponatremia while maintaining adequate effluent volumes 9