What causes hypernatremia?

Causes of Hypernatremia

Hypernatremia (serum sodium >145 mmol/L) is primarily caused by water deficit relative to sodium content, resulting from either inadequate water intake, excessive water loss, or excessive sodium intake. 1

Pathophysiological Classification

Water Loss Mechanisms

• Renal water losses:

  • Diabetes insipidus (central or nephrogenic) 2
  • Osmotic diuresis 3
  • Diuretic use, especially in patients with liver disease 1

• Extrarenal water losses:

  • Gastrointestinal losses (diarrhea, vomiting, fistulas, drainage tubes) 1
  • Excessive sweating, particularly in endurance athletes 1
  • Increased insensible losses (fever, tachypnea, burns) 3
  • Transepidermal water loss, especially in very low birth weight infants 4

Sodium Gain Mechanisms

• Iatrogenic causes:

  • Excessive sodium administration in parenteral nutrition 1
  • Administration of hypertonic NaCl or NaHCO3 solutions 2
  • Incorrect replacement of fluid losses 4
  • Inadequate fluid prescription in hospitalized patients 1

• Pathological causes:

  • Primary hyperaldosteronism (chronic hypervolemic hypernatremia) 2

Clinical Context-Based Classification

Hypervolemic Hypernatremia

• Excessive sodium intake (hypertonic saline, sodium bicarbonate) 2
• Primary hyperaldosteronism 2

Euvolemic Hypernatremia

• Central diabetes insipidus (traumatic, vascular, or infectious causes) 2
• Nephrogenic diabetes insipidus (medication-induced, especially lithium, or hypokalemia) 2
• Inadequate water intake (impaired thirst mechanism, limited access to water) 3

Hypovolemic Hypernatremia

• Renal losses (diuretics, osmotic diuresis) 2
• Extrarenal losses (sweating, diarrhea, burns) 1, 3

Special Populations

Pediatric Considerations

• In very low birth weight infants (VLBWI), hypernatremia is often iatrogenic due to:
  • Incorrect replacement of transepidermal water loss (TEWL) 4
  • Inadequate water intake 4
  • Excessive sodium intake during transition phase 4

Hospitalized Patients

• Hospital-acquired hypernatremia is frequently iatrogenic and preventable 5
• Inadequate fluid prescription is a common cause 1
• Excessive sodium administration in parenteral nutrition 1

Clinical Pitfalls and Caveats

• Hypernatremia is associated with significant morbidity and mortality, requiring prompt recognition and treatment 3

• Clinical presentation often includes central nervous system dysfunction (confusion, coma) and pronounced thirst in conscious patients 6

• Diagnostic approach should include assessment of:

  • Volume status of the patient 6
  • Urine osmolality and sodium measurements 1
  • Duration of hypernatremia (acute vs. chronic) 2

• Treatment considerations:

  • Correction rate should not exceed 10-15 mmol/L/24h for chronic hypernatremia (>48h) to avoid cerebral edema and neurological injury 4, 1
  • Treatment must address the underlying cause while simultaneously correcting water deficit 1
  • For acute hypernatremia (<24 hours), more rapid correction may be appropriate, but caution is still warranted 6

• Monitoring during treatment:

  • Close laboratory monitoring is essential during correction 6
  • Special attention needed when initiating renal replacement therapy in patients with chronic hypernatremia 6