Hyponatremia is the most common electrolyte disorder in adults. 3-6% of patients presenting to the ED are hyponatremic.

• Hyponatremia:
  • mild (135-125 mEq/L).
  • severe (less than 125 mEq/L).

Mild hyponatremia is associated with an increase in mortality (30%) and admission rates (14%).
At-risk populations include patients with:

• • Kidney disease,
  • Congestive heart failure,
  • Liver disease,
  • Diuretics use,
  • Excessive water intake (especially in context of physical activity)
  • Low protein diet and high-water intake.

• Acute hyponatremia = hyponatremia occurring in <48hrs.
• If the acuity cannot be determined assume chronic.
• Severity of symptoms reflects both rapidity of change and sodium level.
• Mild to moderate: headache, nausea, vomiting, muscle cramps.
• Severe symptoms: seizure, coma, delirium, altered level of consciousness.
• Treatment based on patient’s volume status (eg. orthostatic hypotension assessment, moisture of mucus membranes, peripheral edema, JVP, POCUS of IVC diameter, and collapsibility).
• Lab investigations include electrolytes, glucose, creatinine/GFR, urea, urine osmolality, and urine sodium. LFT’s and BNP if clinically indicated.

Acute Symptomatic Hyponatremia

• Acute decrease does not allow time to adapt the osmolality leading to brain swelling and herniation. Therefore, any symptoms require close monitoring – can deteriorate rapidly.
• Treatment for moderate symptoms:
  • Infusion of 3% hypertonic saline at a rate of 0.5-2 mL/kg/hr until symptoms resolve and or sodium is corrected 4-6mEq/L.
• Treatment for severe symptoms:
  •  100-150 mL bolus of 3% hypertonic saline over 10-20 minutes. This can be repeated up to 2 times until symptoms resolve and or sodium is corrected 4-6mEq/L.

*Re-check sodium 1 hour following bolus and infusion initiation and sodium every 4 hours.

Chronic Symptomatic Hyponatremia

• Patient’s osmolality has had the time to adapt to long-term hyponatremia.
• Greater risk of cerebral edema and subsequent osmotic demyelination syndrome (central pontine myelinolysis).
• Treatment of moderate symptoms – 150 ml bolus 3% hypertonic saline.
• Treatment of severe symptoms – 150mL bolus of 3% hypertonic saline given over 10-20 minutes. This can be repeated 1 time until symptoms resolve and or sodium is corrected 4-6mEq/L.
• Re-check sodium 1 hour following bolus and infusion initiation and sodium every 4 hours.

Asymptomatic Hyponatremia (Acute or Chronic)

• Hypovolemic hyponatremia requires fluid resuscitation with normal saline or lactate ringer’s 0.5-1.0mL/kg/hr with the goal of the patient becoming euvolemic. The sodium should be monitored every 6-8hrs.
• Euvolemic hyponatremia mainstay of treatment is a fluid restriction, generally 1-1.5L per day of fluids.
• Hypervolemic hyponatremia also requires fluid restriction of no more than 0.8L per day. For patients with congestive heart failure, chronic kidney disease, nephrotic syndrome, and cirrhosis: loop diuretics and salt restriction can be considered.
• Admit based on their clinical status.

Overcorrection

• Overcorrection = rise > 10mEq/L in the first 24hrs or 8mEq/L if the patient has chronic hyponatremia or sodium was initially <120mEq/L.
• 4-6mEq/L encompasses good clinical effect and appropriate safety margins.
• When overcorrection occurs:
  • Discontinue treatment immediately.
  • Consult nephrologist, endocrinologist.
  • Consider desmopressin.
    • 2-4 micrograms every 8 hours IV.
    • Monitor sodium every hour.

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