What Causes Elevated Sodium Levels
Hypernatremia is predominantly caused by excessive water loss rather than sodium gain, with the most common mechanisms being transepidermal water loss, gastrointestinal losses, renal water losses, and inadequate water intake. 1, 2
Primary Pathophysiological Mechanisms
Hypernatremia develops through three main pathways:
1. Excessive Water Loss (Most Common)
- Transepidermal water loss (TEWL) is particularly significant in very low birth weight infants and burn patients, where voluminous fluid losses occur through damaged or immature skin 1, 2
- Gastrointestinal losses from diarrhea, vomiting, fistulas, or drainage tubes deplete hypotonic fluid 1
- Renal water losses occur in nephrogenic diabetes insipidus and other renal concentrating defects where kidneys cannot adequately concentrate urine 1, 2
- Excessive sweating in endurance athletes without adequate water replacement leads to net water deficit 1
2. Inadequate Water Intake
- Impaired access to water in bedridden patients or those with altered mental status 2
- Impaired thirst mechanisms preventing appropriate water consumption 3
- Transient diabetes insipidus following neurosurgery or traumatic brain injury in neurosurgical patients 2
3. Primary Sodium Excess (Uncommon but Iatrogenic)
- Excessive sodium administration in parenteral nutrition, especially in neonates and patients with renal dysfunction 1, 2
- Hypertonic saline administration in patients with underlying renal concentrating defects 2
- Incorrect fluid prescription in hospitalized patients (most common iatrogenic cause) 1
Population-Specific Causes
Neonates and Premature Infants
- Incorrect replacement of transepidermal water loss is the leading iatrogenic cause 1, 2
- Inadequate water intake during the transition phase relative to insensible losses 1
- Medications causing increased water loss (caffeine, diuretics) 1
Hospitalized Patients
- Inadequate fluid prescription is the most common preventable cause 1, 4
- Excessive diuretic use, particularly in liver disease patients 1
Athletes
- Excessive sweating without adequate water replacement during endurance activities 1
Critical Clinical Pitfalls to Avoid
Never administer isotonic maintenance fluids to patients with significant renal concentrating defects (like nephrogenic diabetes insipidus), as this will worsen hypernatremia—hypotonic fluid replacement is required instead. 2
- Rapid correction of chronic hypernatremia (>48 hours duration) can induce cerebral edema, seizures, and neurological injury 1, 2, 5
- The correction rate should not exceed 10-15 mmol/L per 24 hours for established hypernatremia 1, 2
- Hypernatremic dehydration carries high morbidity and mortality primarily due to CNS dysfunction 2, 5