Why D5 (Dextrose 5% in Water) is Ordered for Hypernatremia
D5W is ordered for hypernatremia because it provides free water without any sodium, allowing correction of the sodium level by diluting the serum sodium concentration while avoiding additional osmotic load on the kidneys. 1
Mechanism and Rationale
Free Water Delivery Without Osmotic Load
- D5W delivers pure free water to correct hypernatremia because the dextrose is rapidly metabolized upon infusion, leaving only water behind 1
- The tonicity of D5W is effectively zero after dextrose metabolism, providing no renal osmotic load 1
- This is critical because salt-containing solutions like normal saline (0.9% NaCl) have an osmolarity of ~300 mOsm/kg H₂O, which would worsen hypernatremia rather than correct it 1
Avoiding Isotonic Fluids in Hypernatremia
- Normal saline should be avoided in hypernatremia because its tonicity (~300 mOsm/kg H₂O) exceeds typical urine osmolality, requiring approximately 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid 1
- This creates a vicious cycle where isotonic fluids actually worsen hypernatremia by providing more sodium than can be excreted 1
Clinical Application
Correction Rate and Safety
- The induced change in serum osmolality should not exceed 3 mOsm/kg H₂O per hour during correction 1
- For chronic hypernatremia (>48 hours), correction should not exceed 8-10 mmol/L per day to prevent osmotic demyelination syndrome 2
- D5W allows controlled, gradual correction at physiological maintenance rates (25-30 mL/kg/24h in adults) 1
Specific Clinical Scenarios
- In nephrogenic diabetes insipidus with hypernatremic dehydration, D5W is the recommended fluid because these patients cannot concentrate urine and will worsen with isotonic fluids 1
- In hyperglycemic crises (DKA/HHS) with hypernatremia, once glucose reaches 250-300 mg/dL, fluids should be changed to D5W with appropriate electrolytes to prevent worsening hypernatremia 1
- In post-surgical hypernatremia (such as after hydatid cyst removal with hypertonic saline exposure), D5W infusions combined with furosemide effectively normalize sodium levels 3
Monitoring During Treatment
- Serum sodium should be monitored frequently (every 2-4 hours initially) during active correction 1
- Fluid replacement should correct estimated deficits within 24 hours while maintaining safe correction rates 1
Common Pitfall to Avoid
Never use isotonic saline (0.9% NaCl) to treat hypernatremia - this will worsen the condition by providing additional sodium load that exceeds the patient's ability to excrete it, particularly in patients with impaired renal concentrating ability 1