Management of Hypernatremia with Elevated BUN
For a patient with sodium 160 mEq/L and BUN 77 mg/dL, administer 5% dextrose in water (D5W) as the primary IV fluid to correct the free water deficit, avoiding normal saline which will paradoxically worsen the hypernatremia. 1
Rationale for D5W Selection
- D5W is the appropriate fluid choice because it delivers no renal osmotic load, allowing controlled correction of the water deficit without adding additional sodium burden that would exacerbate hypernatremia 1
- Normal saline (0.9% NaCl) must be avoided as primary therapy since salt-containing solutions have a tonicity approximately 3-fold higher than typical urine osmolality in hypernatremic states, which will worsen the hypernatremia 1
- The elevated BUN (77 mg/dL) indicates significant volume depletion and prerenal azotemia, confirming the need for free water replacement rather than isotonic saline 2
Calculating the Water Deficit and Infusion Rate
Step 1: Calculate total body water (TBW)
Step 2: Calculate water deficit
- Water deficit = TBW × [(Current Na⁺/Desired Na⁺) - 1] 1
- Target sodium should be 145 mEq/L initially (do not attempt to normalize completely in first 24 hours) 1
Step 3: Determine D5W infusion rate
- Divide total water deficit by 48 hours for initial correction rate 1
- Example: If water deficit is 6 liters, infuse at approximately 125 mL/hour 1
Critical Correction Rate Limits
- The induced change in serum osmolality must not exceed 3 mOsm/kg H₂O per hour to prevent cerebral edema 3, 1
- Target sodium correction should not exceed 8-10 mEq/L per 24 hours 1
- Monitor serum sodium every 4-6 hours during initial correction and adjust D5W rate accordingly 1
Monitoring Parameters
- Check serum sodium, BUN, creatinine, and osmolality every 4-6 hours initially 1
- Assess hemodynamic status through blood pressure monitoring, input/output measurements, and clinical examination for signs of fluid overload 1
- Continue monitoring until osmolality normalizes to <300 mOsm/kg 1
- Monitor mental status frequently, especially if renal or cardiac compromise exists 1
Concurrent Electrolyte Management
- Once renal function is assured, add 20-30 mEq/L potassium to IV fluids (2/3 KCl and 1/3 KPO4) as hypernatremia often coexists with potassium depletion 3, 1
- Address other electrolyte abnormalities concurrently with sodium correction 1
Common Pitfall to Avoid
The most critical error is using 0.9% normal saline as the primary fluid, which paradoxically worsens hypernatremia by providing excessive osmotic load despite appearing to address volume depletion 1. The elevated BUN indicates hypovolemia, but this must be corrected with hypotonic fluid (D5W), not isotonic saline.