Hyponatremia (B) is the most likely explanation for this patient's confusion
In a patient presenting with confusion and a serum sodium of 120 mmol/L, the hyponatremia is the primary cause of her altered mental status and requires immediate attention. While multiple electrolyte abnormalities are present, the severity of hyponatremia at this level directly causes neurological symptoms including confusion, altered sensorium, and can progress to seizures 1.
Why Hyponatremia is the Culprit
Sodium of 120 mmol/L represents severe hyponatremia that crosses the critical threshold for neurological manifestations. Guidelines consistently identify this level as requiring urgent evaluation and treatment 2, 1, 3:
- Serum sodium <120-125 mmol/L is associated with altered mental status, confusion, and seizures 1, 4
- The neurosurgical literature specifically identifies Na <120 mmol/L as the critical level for development of seizures and severe neurological impairment 1
- Symptoms directly correlate with both the magnitude of hyponatremia and the rate of onset 1, 4
Why Not the Other Abnormalities?
Hyperkalemia (K 5.6): While elevated, this level typically does not cause confusion or altered mental status. Hyperkalemia primarily affects cardiac conduction and can cause muscle weakness, but confusion is not a characteristic manifestation 2, 5, 6. The guideline threshold for concern is K >6.0 mEq/L 2.
Hyperglycemia: Without knowing the exact glucose level, hyperglycemia alone rarely causes confusion unless extremely severe (typically >600 mg/dL in hyperosmolar states) 7, 8. Importantly, hyperglycemia actually causes a dilutional hyponatremia - for every 100 mg/dL rise in glucose above normal, sodium decreases by approximately 1.6-2.4 mmol/L 1, 9. This means the "true" sodium may be even lower than 120 mmol/L when corrected for hyperglycemia.
Hypercalcemia: While severe hypercalcemia (>14 mg/dL) can cause cognitive dysfunction and altered mental status 10, mild-to-moderate elevations typically cause fatigue, constipation, and polyuria rather than acute confusion.
Clinical Approach
Immediate priorities for this patient:
- Assess symptom severity and acuity - confusion with Na 120 mmol/L warrants hospitalization 3
- Determine volume status (hypovolemic, euvolemic, or hypervolemic) through physical examination, urine sodium, and urine osmolality 1
- Rule out precipitants - infections, medications (diuretics, laxatives), thyroid/adrenal dysfunction 3
- Correct cautiously - maximum correction of 6-8 mmol/L in first 24 hours to avoid osmotic demyelination syndrome 1
Critical pitfall: The presence of hyperglycemia may mask the true severity of hyponatremia. When glucose is corrected, the sodium may drop further, potentially worsening neurological symptoms 1, 9.
Treatment depends on volume status:
- Hypovolemic: Normal saline infusions 1, 4
- Euvolemic: Fluid restriction, consider salt tablets or vaptans 4
- Hypervolemic: Treat underlying cause, fluid restriction 3
The combination of severe hyponatremia with confusion represents a medical urgency requiring prompt recognition and careful correction to prevent both ongoing neurological injury and iatrogenic complications from overly rapid correction.