Symptoms of Hypernatremia
Clinical Presentation
Hypernatremia primarily manifests with central nervous system dysfunction, ranging from mild symptoms like restlessness and irritability to severe complications including seizures, coma, and death. 1, 2
Mild to Moderate Symptoms
- Intense thirst (in conscious patients with intact thirst mechanism) 2
- Anorexia and nausea/vomiting 2
- Muscle weakness and restlessness 2
- Lethargy and irritability 1, 2
- Mild neurocognitive deficits 1
Severe Symptoms
- Altered mental status progressing to confusion, delirium, and stupor 1, 2
- Seizures 1, 2
- Coma 1, 2, 3
- Acute brain shrinkage leading to vascular rupture, cerebral bleeding, and subarachnoid hemorrhage (particularly with rapid onset) 2
- Brain herniation and death (rare but possible) 1
Important Clinical Context
Severe symptoms typically manifest only when plasma sodium concentrations acutely rise above 158-160 mmol/L 2. The protective thirst mechanism may be absent or impaired in patients with altered mental status, hypothalamic lesions, infants, and elderly individuals 2. Hypernatremic dehydration carries the highest morbidity and mortality rate among all types of dehydration, primarily due to CNS dysfunction 3.
Treatment Approach
Initial Assessment
Determine the duration of hypernatremia (acute <24-48 hours vs. chronic >48 hours), assess volume status, and identify the underlying cause through urine osmolality and sodium measurements. 4, 5
Correction Rate Guidelines
For chronic hypernatremia (>48 hours), reduce sodium by no more than 10-15 mmol/L per 24 hours to prevent cerebral edema, seizures, and neurological injury. 4, 2, 6
- Maximum safe correction rate: 8-12 mmol/L per day for chronic cases 2, 6
- Acute hypernatremia (<24 hours) can be corrected more rapidly without significant risk of cerebral edema 4, 6
- Overly rapid correction of chronic hypernatremia causes cerebral edema as organic osmolytes accumulated during adaptation are slow to leave cells during rehydration 2
Fluid Replacement Strategy
Use hypotonic fluids (0.45% NaCl, 0.18% NaCl, or D5W) for correction when sodium is severely elevated, patients are symptomatic, or intravenous therapy is required. 1
- For hypovolemic hypernatremia: Replace volume deficit first, then address free water deficit 5
- For euvolemic hypernatremia: Replace free water deficit with hypotonic solutions 5
- For hypervolemic hypernatremia: Address underlying cause and consider diuretics with hypotonic fluid replacement 5
Special Considerations
- Diabetes insipidus: Treat with desmopressin (Minirin) in addition to fluid replacement 6
- Neonates and very low birth weight infants: Require particularly careful correction with daily monitoring of weight and serum electrolytes 4
- Acute hypernatremia (<24 hours): Hemodialysis is an effective option for rapid normalization, though sodium drop must still be controlled 6
Monitoring Requirements
- Frequent laboratory monitoring is essential to avoid both undercorrection and overcorrection, both associated with poor prognosis 4
- Close monitoring of serum sodium every 2-4 hours during active correction 6
- Daily weight monitoring in neonates 4
Critical Pitfall to Avoid
Never correct chronic hypernatremia faster than 10-15 mmol/L per 24 hours—rapid correction induces cerebral edema, seizures, and permanent neurological injury due to the brain's adaptation mechanisms. 4, 2, 6