What causes hypernatremia?

Causes of Hypernatremia

Hypernatremia fundamentally results from an imbalance where water content is deficient relative to sodium content in body fluids, most commonly due to water loss rather than sodium excess. 1, 2, 3

Primary Pathophysiological Mechanisms

Hypernatremia occurs through two main pathways: water loss (most common) or sodium gain (rare). 3

Water Loss Mechanisms

• Gastrointestinal losses including diarrhea, vomiting, fistulas, or drainage tubes cause hypernatremia by depleting hypotonic fluids 4
• Excessive sweating, particularly in endurance athletes without adequate water replacement, leads to disproportionate water loss 4
• Transepidermal water loss (TEWL) is especially significant in very low birth weight infants and severe burn patients, causing voluminous fluid losses 4
• Renal concentrating defects such as nephrogenic diabetes insipidus impair the kidney's ability to conserve water 4
• Impaired thirst mechanism or lack of access to water commonly causes mild hypernatremia, particularly in elderly or debilitated patients 5

Sodium Excess Mechanisms

• Excessive sodium administration in parenteral nutrition can cause hypernatremia, particularly in patients with renal dysfunction or extrarenal free-water losses 4
• Incorrect replacement of transepidermal water loss in very low birth weight infants represents a leading iatrogenic cause 4

Context-Specific Causes by Clinical Setting

Hospitalized Patients

• Inadequate fluid prescription is the most common iatrogenic cause in hospital settings 4
• Excessive diuretic use can cause hypovolemic hypernatremia, particularly in patients with liver disease 4

Neonatal and Pediatric Populations

• Incorrect TEWL replacement in premature infants is the leading cause 4
• Inadequate water intake during the transition phase contributes to hypernatremia in neonates 4
• Medications causing increased water loss such as caffeine and diuretics in premature infants 4

Athletes

• Excessive sweating without adequate water replacement during endurance activities 4

Underlying Physiological Dysfunction

Hypernatremia develops when dysfunction occurs in all three normal regulatory mechanisms: Arginine Vasopressin (AVP) secretion, thirst response, and renal response to AVP. 2 Normal osmolality is maintained between 280-295 mOsm/kg through these integrated systems 2

Diagnostic Approach to Determine Etiology

• Urine osmolality and sodium measurements help determine whether kidneys are appropriately concentrating urine and guide identification of renal versus extrarenal causes 4
• Volume status assessment combined with medical history and urine osmolality leads the differential diagnosis 1

Critical Clinical Pitfalls

• Rapid correction of chronic hypernatremia (>48 hours) can induce cerebral edema, seizures, and neurological injury; correction should not exceed 10-15 mmol/L per 24 hours 4, 1
• Hypernatremia is associated with high mortality, particularly hypernatremic dehydration which carries the highest morbidity and mortality rate among dehydration types, primarily related to CNS dysfunction 6, 3