Treatment of Severe Hypernatremia
For a 74.4 kg patient with severe hypernatremia, administer hypotonic fluids (0.45% NaCl or D5W) to replace the free water deficit, with a maximum correction rate of 10-15 mmol/L per 24 hours to prevent cerebral edema. 1
Immediate Assessment
Calculate the free water deficit using the formula: Water deficit = 0.5 × body weight (kg) × [(current Na/140) - 1] 1
- For this 74.4 kg patient, if sodium is severely elevated (e.g., >160 mmol/L), the deficit will guide total fluid replacement
Determine the chronicity: Acute hypernatremia (<48 hours) can be corrected more rapidly (up to 1 mmol/L/hour if severely symptomatic), while chronic hypernatremia (>48 hours) requires slower correction at 10-15 mmol/L per 24 hours 1, 2
Assess volume status and neurological symptoms: Look for confusion, altered mental status, seizures, or coma, which indicate severe CNS dysfunction requiring urgent intervention 2, 3
Fluid Selection and Administration
Primary fluid choice is D5W (5% dextrose in water) as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 1
Alternative option: 0.45% NaCl (half-normal saline) containing 77 mEq/L sodium with osmolarity ~154 mOsm/L for moderate cases 1
Never use isotonic saline (0.9% NaCl) as initial therapy, as it delivers excessive osmotic load—requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid, which worsens hypernatremia 1
Initial fluid rate for adults: 25-30 mL/kg/24 hours, which for this 74.4 kg patient equals approximately 1,860-2,232 mL per 24 hours 1
Critical Correction Rate Guidelines
The absolute maximum correction rate is 10-15 mmol/L per 24 hours for chronic hypernatremia to prevent cerebral edema, seizures, and permanent neurological injury 1, 2
Brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions 1
Rapid correction causes water to shift into brain cells faster than osmolytes can be eliminated, resulting in cerebral edema 1
For acute hypernatremia (<24 hours) with severe symptoms: Correction up to 1 mmol/L/hour may be acceptable 1
Monitoring Protocol
Check serum sodium every 2-4 hours initially during active correction to ensure the rate does not exceed safe limits 1, 2
Monitor for signs of cerebral edema: Worsening confusion, headache, seizures, or declining level of consciousness during correction 1, 3
Assess renal function and urine osmolality regularly, as these guide ongoing fluid management 1
Special Considerations
If the patient has nephrogenic diabetes insipidus or renal concentrating defects, ongoing hypotonic fluid administration is required to match excessive free water losses, and isotonic fluids will worsen hypernatremia 1
For patients with heart failure and hypernatremia, implement sodium and fluid restriction (limiting fluid to around 2 L/day), and consider vasopressin antagonists (tolvaptan, conivaptan) for short-term use only if persistent severe hypernatremia with cognitive symptoms 1
If the patient has cirrhosis with hypervolemic hypernatremia, focus on achieving negative water balance rather than aggressive fluid administration, with close monitoring of serum sodium and fluid status 1
Common Pitfalls to Avoid
Correcting chronic hypernatremia too rapidly leads to cerebral edema, seizures, and permanent neurological injury 1, 2
Using isotonic saline in patients with renal concentrating defects exacerbates hypernatremia 1
Failing to monitor sodium levels frequently during correction risks overshooting the safe correction rate 2