Management of Severe Hypernatremia (Sodium 158 mEq/L)
For a patient with severe hypernatremia (sodium 158 mEq/L), initiate treatment with hypotonic fluids such as 0.45% NaCl or 5% dextrose in water (D5W), targeting a maximum correction rate of 10-12 mmol/L per 24 hours to prevent cerebral edema. 1, 2
Immediate Assessment
Before initiating correction, determine the underlying mechanism:
- Check for sodium gain vs. water loss through clinical assessment of volume status (orthostatic vital signs, skin turgor, mucous membranes) and urine electrolytes 3
- Assess mental status carefully – altered consciousness, lethargy, irritability, or stupor indicate severe hypernatremia requiring urgent intervention 4
- Evaluate thirst mechanism – elderly patients, those with altered mental status, hypothalamic lesions, or infants may have impaired thirst sensation and are at highest risk 4
- Look for acute neurological signs including seizures, confusion, muscle weakness, or restlessness that suggest rapid onset 2, 4
Fluid Selection and Administration
Primary fluid choice is D5W (5% dextrose in water) because it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 1
Alternative options include:
- 0.45% NaCl (half-normal saline) containing 77 mEq/L sodium for moderate hypernatremia 1
- 0.18% NaCl (quarter-normal saline) with 31 mEq/L sodium for more aggressive free water replacement 1
Avoid isotonic saline (0.9% NaCl) as it delivers excessive osmotic load – requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid, which risks worsening hypernatremia 1
Critical Correction Rate Guidelines
Maximum correction rate: 10-12 mmol/L per 24 hours (approximately 0.4 mmol/L/hour) 1, 4
- Slower correction (≤12 mEq/L/day) is mandatory to prevent cerebral edema, as organic osmolytes accumulated during adaptation are slow to leave cells during rehydration 4
- More rapid correction causes cerebral edema because the relatively hypertonic intracellular fluid accumulates water when extracellular tonicity drops too quickly 4
Initial Fluid Administration Rates
For adults: 25-30 mL/kg/24 hours 1
For children: Calculate based on physiological maintenance:
- 100 mL/kg/24 hours for first 10 kg
- 50 mL/kg/24 hours for 10-20 kg
- 20 mL/kg/24 hours for remaining weight 1
Monitoring Protocol
- Check serum sodium every 2-4 hours initially during active correction 1, 2
- Monitor neurological status closely for signs of cerebral edema (worsening mental status, seizures) or improvement 2, 4
- Track urine output and ongoing losses to adjust replacement accordingly 3
- Assess volume status serially through vital signs, physical examination, and fluid balance 3
Special Considerations
For patients with nephrogenic diabetes insipidus or renal concentrating defects:
- Ongoing hypotonic fluid administration is required to match excessive free water losses 1
- Isotonic fluids will worsen hypernatremia in these patients 1
High-risk populations (infants, malnourished patients):
- Consider smaller-volume frequent boluses (10 mL/kg) due to reduced cardiac output capacity 1
Prognostic Factors
Age and initial sodium concentration are the most important prognostic indicators:
- Very young patients have better survival rates 5
- Patients with lesser degrees of hypernatremia (closer to 158 vs. >200 mEq/L) have better outcomes 5
- Initial serum sodium >200 mEq/L carries extremely high mortality despite treatment 5, 6
Common Pitfalls to Avoid
- Never correct faster than 12 mEq/L per 24 hours – this causes cerebral edema as the primary complication 4
- Never use isotonic saline for correction – it provides inadequate free water and can worsen hypernatremia 1
- Never delay treatment in symptomatic patients – severe symptoms (seizures, altered consciousness) require immediate hypotonic fluid therapy 2, 4
- Never assume adequate thirst mechanism in elderly, confused, or institutionalized patients – these populations require active fluid management by clinicians 3, 4