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    Hyponatremia – Diagnosis and Treatment

    Cardiovascular, Hematological / Oncological, Metabolic / Endocrine

    Last Updated Oct 29, 2021
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    By Anne Davies, Kala Draney


    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.

    Diagnostic Process

    • 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.

    Recommended Treatment

    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 = 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.

    Quality Of Evidence?


    Moderate evidence – various guidelines and reviews have similar diagnostic approach and management. However, the quality of reliable research is not high.


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