Management of Hypernatremia with Normal Renal Function
Critical Assessment
Your patient does NOT have hypernatremia—the sodium of 145 mEq/L is within normal range (135-145 mEq/L), and this patient requires no specific intervention for sodium management. 1
However, the low BUN of 7 mg/dL warrants attention as it may indicate inadequate protein intake, liver disease, or overhydration. 2
If This Were True Hypernatremia (Na >145 mEq/L): Management Algorithm
Step 1: Determine Acuity and Severity
- Acute hypernatremia (<24-48 hours): Can correct more rapidly, up to 1 mEq/L/hour initially 3
- Chronic hypernatremia (>48 hours): Must correct slowly at no more than 8-10 mEq/L per day to prevent osmotic demyelination syndrome 3, 4
- Severe symptoms (confusion, seizures, coma) require immediate intervention 1, 5
Step 2: Calculate Free Water Deficit
Use the formula: Water deficit (L) = 0.6 × body weight (kg) × [(current Na/140) - 1] 4
Step 3: Select Replacement Fluid
- Hypotonic saline (0.45% NaCl) is the primary choice for hypernatremia with normal renal function 2, 1
- Administer at 4-14 ml/kg/h after initial assessment 2
- D5W (5% dextrose in water) can be used for pure water replacement in severe cases 4
- Avoid isotonic saline (0.9% NaCl) as it will worsen hypernatremia 1
Step 4: Monitor Correction Rate
- Check serum sodium every 4-6 hours during active correction 6, 4
- Adjust infusion rate to maintain safe correction speed 4
- Monitor for signs of cerebral edema if correcting too rapidly (headache, altered mental status, seizures) 3, 5
Step 5: Replace Ongoing Losses
- Calculate and replace insensible losses (approximately 500-1000 mL/day) 4
- Add measured ongoing losses from urine, drains, or other sources 4
- Adjust total fluid administration accordingly 2
Step 6: Address Underlying Cause
- Diabetes insipidus: Consider desmopressin (Minirin) 3
- Inadequate water intake: Ensure access to free water 1, 7
- Excessive losses: Identify and control source 7, 4
Key Monitoring Parameters
- Serum sodium: Every 4-6 hours initially, then every 12-24 hours once stable 6, 4
- Urine output and osmolality: Helps differentiate causes and guide therapy 4
- Volume status: Blood pressure, heart rate, signs of dehydration or overload 2, 6
- Neurological status: Mental status changes indicate either inadequate or overly rapid correction 3, 5
Critical Pitfalls to Avoid
- Never correct chronic hypernatremia faster than 8-10 mEq/L per day—this causes osmotic demyelination syndrome with permanent neurological damage 3, 4
- Never use isotonic (0.9%) saline for hypernatremia—it contains 154 mEq/L sodium and will worsen the condition 1
- Never delay treatment while pursuing diagnostic workup if patient is symptomatic 1
- Never ignore ongoing losses—failure to replace these will result in inadequate correction 4
- Never assume hypernatremia equals dehydration—rare cases involve sodium excess requiring different management 3, 7
Special Consideration for Your Patient's Low BUN
The BUN of 7 mg/dL (normal 7-20 mg/dL) combined with normal sodium suggests:
- Possible overhydration or excessive fluid intake 2
- Low protein intake or malnutrition 2
- Liver disease with impaired urea synthesis 2
This requires clinical correlation with volume status examination and consideration of nutritional assessment. 2