What is the treatment for acute hyponatremia?

Treatment of Acute Hyponatremia

For acute hyponatremia (<48 hours) with severe symptoms (seizures, coma, altered mental status), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, with a maximum total correction of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2

Immediate Assessment and Classification

• Determine acuity: Acute hyponatremia is defined as onset <48 hours, typically hospital-acquired in postoperative states or after excessive fluid administration 1, 3
• Assess symptom severity: Severe symptoms include seizures, respiratory arrest, coma, somnolence, obtundation, or cardiorespiratory distress 1, 2, 4
• Check volume status: Evaluate for signs of hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor), euvolemia, or hypervolemia (edema, ascites, jugular venous distention) 1
• Obtain initial labs: Serum and urine osmolality, urine sodium, urine electrolytes, and serum uric acid 1

Treatment Based on Symptom Severity

Severe Symptomatic Acute Hyponatremia

Hypertonic saline administration:

• Give 100 mL of 3% hypertonic saline IV over 10 minutes as first-line treatment 2
• Repeat 100 mL bolus every 10 minutes if symptoms persist, up to three total boluses 2
• Target initial sodium increase of 4-6 mEq/L in first 1-2 hours to abort severe symptoms 2, 4, 5
• Correct by 6 mmol/L over first 6 hours or until severe symptoms resolve 1, 2
• Maximum total correction: 8 mmol/L in 24 hours 1, 2, 4

Critical safety point: If 6 mmol/L is corrected in the first 6 hours, limit additional correction to only 2 mmol/L in the following 18 hours 2

Asymptomatic or Mildly Symptomatic Acute Hyponatremia

• Slower correction is appropriate, targeting 4-8 mmol/L per day 1
• Treatment should focus on addressing the underlying cause 1

Monitoring Protocol

During active correction:

• Check serum sodium every 2 hours during initial correction phase for severe symptoms 1, 2
• Monitor strict intake and output 2
• Obtain daily weights 2
• After symptom resolution, check sodium every 4 hours 1

Watch for overcorrection:

• If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue hypertonic saline and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse rapid rise 1

Treatment Based on Underlying Etiology

SIADH (Euvolemic)

• After acute phase stabilization, implement fluid restriction to 1 L/day 1, 2
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1, 2

Cerebral Salt Wasting (CSW)

• Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1, 2
• For severe symptoms, use 3% hypertonic saline plus fludrocortisone in ICU setting 1, 2
• In subarachnoid hemorrhage patients at risk of vasospasm, avoid fluid restriction 1, 2

Hypovolemic Hyponatremia

• Discontinue diuretics immediately 1
• Administer isotonic (0.9%) saline for volume repletion 1
• Correction rate should not exceed 8 mmol/L in 24 hours 1

Critical Distinction: Acute vs. Chronic

Acute hyponatremia (<48 hours) can be corrected rapidly without risk of osmotic demyelination syndrome 1, 3, 6

This is fundamentally different from chronic hyponatremia (>48 hours), where rapid correction carries significant risk of osmotic demyelination. In acute hyponatremia, the brain has not yet completed adaptive mechanisms (extrusion of electrolytes and organic osmolytes), which takes approximately 48 hours 3. Therefore, prompt and relatively rapid correction is both safe and necessary to prevent severe neurological complications including seizures, respiratory arrest, and death 1, 3, 6.

Common Pitfalls to Avoid

• Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1, 2
• Avoid fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1, 2
• Do not exceed 8 mmol/L correction in 24 hours, even in acute hyponatremia, to maintain safety margin 1, 2
• Inadequate monitoring during active correction can lead to overcorrection 1
• Failing to distinguish between SIADH and cerebral salt wasting leads to inappropriate treatment 1, 2

Special Populations Requiring Caution

Even in acute hyponatremia, certain high-risk populations may benefit from more conservative correction rates (4-6 mmol/L per day):

• Advanced liver disease 1
• Alcoholism 1
• Malnutrition 1
• Prior encephalopathy 1

Alternative Treatment: Urea

Urea represents an advantageous alternative to hypertonic saline for acute hyponatremia 7, 3:

• Allows rapid reduction of brain edema and intracranial pressure 3
• Experimental data suggest lower incidence of myelinolysis compared to hypertonic saline 3
• Dosing: 40 g of urea in 100-150 mL normal saline every 8 hours, plus continuous normal saline infusion at 60-100 mL/h for 1-2 days 1