What causes severe hyponatremia (sodium level of 107 mmol/L)?

Causes of Severe Hyponatremia (Sodium 107 mmol/L)

A sodium level of 107 mmol/L represents life-threatening severe hyponatremia that requires immediate evaluation of volume status and underlying etiology to guide emergency treatment. 1

Primary Mechanisms and Common Causes

Severe hyponatremia results from water retention relative to sodium stores, with the specific cause determined by volume status 1, 2:

Hypovolemic Hyponatremia (Volume Depleted)

• Excessive diuretic use, particularly in patients with liver cirrhosis, causing renal sodium losses 1
• Gastrointestinal losses from severe diarrhea, vomiting, or other GI fluid losses 3
• Renal losses from salt-wasting nephropathy or mineralocorticoid deficiency 1
• Clinical signs include hypotension, tachycardia, dry mucous membranes, and decreased skin turgor 1
• Urinary sodium typically <30 mmol/L in extrarenal losses, >20 mmol/L in renal losses 1

Euvolemic Hyponatremia (Normal Volume Status)

• Syndrome of Inappropriate ADH (SIADH) - the most common cause in this category 1, 2
  • Malignancies (especially small cell lung cancer) 1
  • CNS disorders (meningitis, encephalitis, head trauma, subarachnoid hemorrhage) 1
  • Pulmonary diseases (pneumonia, tuberculosis) 1
  • Medications (SSRIs, carbamazepine, NSAIDs, opiates) 1
• Cerebral salt wasting (CSW) in neurosurgical patients, caused by excessive natriuretic peptide secretion 1
• Hypothyroidism or adrenal insufficiency (must be ruled out) 1
• Beer potomania - severe hyponatremia from excessive beer consumption with poor solute intake 1
• Primary polydipsia - excessive free water intake 4

Hypervolemic Hyponatremia (Volume Overloaded)

• Advanced liver cirrhosis with portal hypertension - systemic vasodilation leads to decreased effective plasma volume, activating renin-angiotensin-aldosterone system causing excessive sodium and water reabsorption 1
• Congestive heart failure with impaired free water clearance 1, 2
• Nephrotic syndrome or advanced kidney disease 1
• Clinical signs include edema, ascites, jugular venous distention, and orthopnea 1

Critical Diagnostic Features

For sodium of 107 mmol/L, immediately assess:

• Symptom severity - confusion, seizures, coma indicate hyponatremic encephalopathy requiring emergency treatment 1, 4
• Acuity of onset - acute (<48 hours) versus chronic (>48 hours) determines correction rate and risk of complications 1, 5
• Volume status - hypovolemic, euvolemic, or hypervolemic guides treatment approach 1, 2
• Urine osmolality and sodium - urine osmolality >100 mOsm/kg with urine sodium >20 mmol/L suggests SIADH or CSW 1
• Serum osmolality - should be low (<280 mOsm/kg) in true hyponatremia 1

High-Risk Populations

Patients at increased risk for severe hyponatremia include:

• Those with advanced liver disease, alcoholism, or malnutrition (higher risk of osmotic demyelination with correction) 1
• Elderly patients on multiple medications 2
• Endurance athletes with excessive free water intake during exercise 6, 4
• Neurosurgical patients (21% incidence in subarachnoid hemorrhage) 1

Clinical Significance

Severe hyponatremia with sodium ≤120 mmol/L is associated with:

• 60-fold increase in mortality (11.2% versus 0.19% in normonatremic patients) 1
• Increased fall risk (21% versus 5% in normonatremic patients) 1
• Life-threatening cerebral edema if untreated 5
• Risk of osmotic demyelination syndrome if corrected too rapidly (>8 mmol/L in 24 hours) 1, 5

Common Pitfalls to Avoid

• Failing to recognize severe symptoms requiring immediate hypertonic saline 1
• Delaying treatment while pursuing diagnostic workup - treatment should not be delayed 4
• Misdiagnosing volume status leading to inappropriate fluid management 1
• Using fluid restriction in cerebral salt wasting (worsens outcomes) 1
• Overly rapid correction exceeding 8 mmol/L in 24 hours, risking osmotic demyelination syndrome 1, 5
• Ignoring medication review - many common drugs cause hyponatremia 1