Serum Sodium 146 mEq/L: Mild Hypernatremia
A serum sodium of 146 mEq/L represents mild hypernatremia, defined as a sodium level above 145 mEq/L, which typically indicates a relative water deficit compared to total body sodium. 1
Clinical Significance
- Hypernatremia occurs when serum sodium exceeds 145 mEq/L, reflecting either net water loss or, less commonly, sodium gain 1
- The human body normally maintains osmolality between 280-295 mOsm/kg through arginine vasopressin (AVP), thirst mechanism, and renal response to AVP 1
- Dysfunction in any of these three regulatory mechanisms can lead to hypernatremia 1
Most Common Etiology in Hospital Settings
In intensive care units, hypervolemic hypernatremia is the most common type, often occurring in patients recovering from acute kidney injury (AKI) who have received large volumes of saline. 2
- These patients typically present with edema and significant weight gain (average >9 kg) despite developing hypernatremia 2
- Post-AKI diuresis combined with impaired urinary concentrating ability leads to predominantly water loss with urine osmolality averaging 436 mmol/kg 2
- Even though patients may be in negative fluid balance at the time hypernatremia develops, earlier aggressive saline administration causes persistent volume overload 2
Pathophysiology
The development of hypernatremia requires:
- Inadequate water intake relative to losses 1
- Impaired thirst mechanism or lack of access to free water 3
- Excessive water losses (renal or extrarenal) that exceed intake 1
Management Approach
For mild hypernatremia (146 mEq/L), identify and address the underlying cause while providing appropriate fluid replacement. 1, 3
Assessment Steps:
- Determine volume status through physical examination (assess for edema, orthostatic changes, mucous membranes) 3
- Calculate free water deficit if needed 3
- Check urine osmolality and sodium to differentiate renal versus extrarenal losses 3
- Review recent fluid administration, particularly isotonic saline volumes 2
Treatment Strategy:
- For hypervolemic hypernatremia (most common in ICU): Restrict sodium intake and allow diuresis while replacing losses with hypotonic fluids 2
- For hypovolemic hypernatremia: Provide volume resuscitation with hypotonic fluids (0.45% saline or D5W) 3
- Correction rate: Avoid decreasing sodium faster than 10-12 mEq/L per 24 hours to prevent cerebral edema 3
- Monitor serum sodium frequently during correction (every 4-6 hours initially) 3
Critical Pitfalls to Avoid
- Do not administer isotonic saline (0.9% NaCl) to patients with hypernatremia, as this delivers 154 mEq/L of sodium and will worsen the condition 4
- Avoid overly rapid correction, which can cause cerebral edema, particularly in chronic hypernatremia 3
- In patients with renal concentrating defects, isotonic fluids will exacerbate hypernatremia 4
- Failing to recognize hypervolemic hypernatremia in post-AKI patients who appear volume overloaded despite elevated sodium 2