The Correct Answer is E
Statement E is NOT true: hypernatremia is corrected with hypotonic solutions (free water replacement), not hypertonic solutions. Administering hypertonic solutions would worsen hypernatremia by adding more sodium.
Analysis of Each Statement
A) Sodium concentration >145 mmol/L - TRUE
Hypernatremia is universally defined as serum sodium >145 mmol/L 1, 2, 3. This threshold represents the standard diagnostic criterion across all clinical contexts.
B) All patients have high blood osmolality - TRUE
Hypernatremia invariably reflects hyperosmolality because sodium is the primary determinant of serum osmolality 1. The condition represents a relative deficiency of free water rather than sodium excess, but the net result is always elevated plasma osmolality. Even in cases of pseudohypernatremia (which must be excluded diagnostically), true hypernatremia always produces hyperosmolality 4.
C) Treatment involves water administration and correcting fluid loss - TRUE
The fundamental treatment principle is restoring water balance 5, 3. Management requires:
- Calculating and replacing the free water deficit using hypotonic fluids (typically 5% dextrose in water or 0.45% saline)
- Addressing ongoing losses (renal, gastrointestinal, or insensible)
- Identifying and treating the underlying cause (diabetes insipidus, dehydration, impaired thirst mechanism)
The correction rate must be controlled: no faster than 0.4 mmol/L/hour for chronic hypernatremia (>48 hours) to prevent cerebral edema 2. For acute hypernatremia (<48 hours), more rapid correction is safer but still requires monitoring 5.
D) Low urine osmolality establishes diabetes insipidus - TRUE
In the diagnostic workup of hypernatremia, inappropriately dilute urine (low osmolality) in the setting of hyperosmolar serum confirms diabetes insipidus 4, 3. Normal kidneys should maximally concentrate urine when plasma osmolality is elevated. Finding urine osmolality <300 mOsm/kg with serum hyperosmolality indicates either:
- Central diabetes insipidus (AVP deficiency)
- Nephrogenic diabetes insipidus (renal resistance to AVP)
This can be further differentiated by measuring copeptin/AVP levels or performing a desmopressin challenge 4.
E) Corrected with hypertonic solutions - FALSE
This statement is fundamentally incorrect and dangerous. Hypernatremia requires hypotonic fluid replacement 5, 3, 6. The specific approach depends on volume status:
- Hypovolemic hypernatremia: Initial resuscitation with isotonic saline to restore hemodynamics, then switch to hypotonic fluids (0.45% saline or 5% dextrose) for sodium correction 6
- Euvolemic hypernatremia: Hypotonic fluids (5% dextrose in water preferred) 3
- Hypervolemic hypernatremia: Free water replacement with possible diuretics to remove excess sodium 2
Administering hypertonic solutions (3% saline) would exacerbate hypernatremia and is only indicated for severe symptomatic hyponatremia, not hypernatremia 3.
Clinical Pitfalls
Critical error to avoid: Confusing the treatment of hypernatremia with hyponatremia. The 3% hypertonic saline used for severe symptomatic hyponatremia would be catastrophic in hypernatremia 3.
Overcorrection risk: Rapid correction of chronic hypernatremia can cause cerebral edema as brain cells that have adapted to hyperosmolality suddenly swell when osmolality drops too quickly 5, 2. Monitor sodium every 2-4 hours during active correction.