What causes hypernatremia?

Causes of Hypernatremia

Hypernatremia most commonly results from water deficit rather than sodium excess, with iatrogenic causes (inadequate water replacement, excessive sodium administration) and extrarenal water losses (diarrhea, vomiting, excessive sweating) being the predominant mechanisms. 1

Primary Pathophysiological Mechanisms

Water Loss (Most Common)

Extrarenal water losses:

• Gastrointestinal losses including diarrhea, vomiting, fistulas, or drainage tubes 1
• Excessive sweating, particularly in endurance athletes without adequate water replacement 1
• Transepidermal water loss (TEWL), especially critical in very low birth weight infants 2, 1
• Severe burns with voluminous fluid losses 2

Renal water losses:

• Diabetes insipidus (central or nephrogenic), which impairs renal concentrating ability 2, 3
• Renal concentrating defects such as nephrogenic diabetes insipidus 2
• Excessive diuretic use, particularly in patients with liver disease 1

Sodium Excess (Less Common)

Iatrogenic sodium administration:

• Excessive sodium intake during parenteral nutrition, which can be inadvertent 2, 1
• Incorrect fluid prescription in hospitalized patients 1
• Hypertonic saline administration 3

Context-Specific Causes by Population

Neonates and Premature Infants

• Incorrect replacement of transepidermal water loss (TEWL) in very low birth weight infants is the leading iatrogenic cause 2, 1
• Inadequate water intake during the transition phase 2
• Excessive inadvertent sodium intake during parenteral nutrition 2

Hospitalized Patients

• Inadequate fluid prescription is the most common iatrogenic cause 1
• Patients with renal dysfunction or extrarenal free-water losses 2

Athletes

• Excessive sweating without adequate water replacement during endurance activities 1

Patients with Chronic Disease

• Excessive diuretic use in liver disease causing hypovolemic hypernatremia 1
• Heart failure or cirrhosis with inappropriate fluid management 3

Diagnostic Approach to Determine Etiology

Volume status assessment is critical:

• Hypovolemic hypernatremia suggests water loss exceeding sodium loss (diarrhea, vomiting, diuretics) 3, 4
• Euvolemic hypernatremia suggests pure water loss (diabetes insipidus, insensible losses) 3, 4
• Hypervolemic hypernatremia suggests sodium excess (iatrogenic sodium administration) 3, 4

Urine studies guide diagnosis:

• Urine osmolality and sodium measurements determine if kidneys are appropriately concentrating urine 1
• High urine osmolality (>600-800 mOsm/kg) suggests extrarenal water loss 4
• Low urine osmolality (<300 mOsm/kg) suggests diabetes insipidus 4

Critical Clinical Pitfalls

Rapid correction causes severe complications:

• Rapid correction of chronic hypernatremia (>48 hours) induces cerebral edema, seizures, and neurological injury 2, 5
• The rate of correction should not exceed 10-15 mmol/L per 24 hours for chronic hypernatremia 2, 1, 5
• For acute hypernatremia (<24 hours), more rapid correction may be appropriate 5

Overlooked causes in specific populations:

• Impaired thirst mechanism or lack of access to water in elderly or disabled patients 3
• Medications causing increased water loss (caffeine, diuretics in premature infants) 2