How is acute hyponatremia treated?

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, but never exceed 8 mmol/L total correction in 24 hours. 1

Initial Assessment and Classification

Determine the acuity of onset—acute (<48 hours) versus chronic (>48 hours)—as this fundamentally changes your correction strategy and risk profile. 1 Acute hyponatremia carries higher risk of cerebral edema and herniation but lower risk of osmotic demyelination syndrome with rapid correction. 1, 2

Assess symptom severity immediately:

• Severe symptoms: seizures, coma, somnolence, obtundation, cardiorespiratory distress 1, 2
• Mild symptoms: nausea, vomiting, headache, weakness 1, 3
• Asymptomatic: no neurological manifestations 1

Check volume status through physical examination looking for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemic); jugular venous distention, peripheral edema, ascites (hypervolemic); or absence of these findings (euvolemic). 1

Treatment Algorithm Based on Symptom Severity

Severe Symptomatic Acute Hyponatremia

Administer 3% hypertonic saline immediately as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve. 1 The American Academy of Neurology recommends targeting an initial correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 4

Calculate the infusion rate using: body weight (kg) × desired rate of increase in sodium (mmol/L per hour). 1, 5 For example, a 70 kg patient targeting 1 mmol/L per hour would receive approximately 70 mL/hour of 3% saline initially.

Critical safety parameter: Do not exceed 8 mmol/L total correction in 24 hours. 1, 4, 2 After achieving the initial 6 mmol/L correction, limit further correction to only 2 mmol/L in the following 18 hours. 4

Monitor serum sodium every 2 hours during initial correction. 1 Once severe symptoms resolve, discontinue 3% saline and transition to protocols for mild symptoms or asymptomatic management. 4

Mild Symptomatic or Asymptomatic Acute Hyponatremia

Treatment depends on the underlying etiology:

For SIADH (euvolemic):

• Implement fluid restriction to 1 L/day as the cornerstone of treatment 1, 5
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• Monitor sodium levels every 4 hours initially, then daily 1

For hypovolemic hyponatremia:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1
• A urinary sodium <30 mmol/L predicts 71-100% response to saline infusion 1

For hypervolemic hyponatremia (heart failure, cirrhosis):

• Implement fluid restriction to 1-1.5 L/day 1, 5
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms are present 1

Special Populations Requiring Cautious Correction

Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require even more conservative correction rates of 4-6 mmol/L per day due to substantially higher risk of osmotic demyelination syndrome. 1, 2 These patients have an estimated 0.5-1.5% risk of osmotic demyelination syndrome even with appropriate correction. 1

Neurosurgical Patients: Critical Distinction

In neurosurgical patients, cerebral salt wasting (CSW) is more common than SIADH and requires fundamentally different treatment. 1 CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction. 1 Using fluid restriction in CSW worsens outcomes. 1

For subarachnoid hemorrhage patients at risk of vasospasm, avoid fluid restriction entirely and consider fludrocortisone or hydrocortisone to prevent natriuresis. 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1 Consider administering desmopressin to slow or reverse the rapid rise in serum sodium. 1 The goal is to bring the total 24-hour correction to no more than 8 mmol/L from the starting point. 1

Common Pitfalls to Avoid

Failing to distinguish acute from chronic hyponatremia leads to inappropriate correction rates. 1, 2 Acute hyponatremia (particularly <48 hours) can be corrected more rapidly initially without risk of osmotic demyelination syndrome, whereas chronic hyponatremia requires strict adherence to the 8 mmol/L per 24-hour limit. 1, 6

Inadequate monitoring during active correction can result in overly rapid correction and osmotic demyelination syndrome. 1 Check sodium levels every 2 hours during hypertonic saline administration for severe symptoms, and every 4 hours after symptom resolution. 1, 4

Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload and ascites. 1 These patients require fluid restriction and management of the underlying condition (heart failure, cirrhosis), not sodium administration. 1

Confusing SIADH with cerebral salt wasting in neurosurgical patients leads to dangerous treatment errors, as fluid restriction (appropriate for SIADH) worsens outcomes in CSW. 1 CSW presents with evidence of volume depletion (hypotension, tachycardia, dry mucous membranes) and requires aggressive volume replacement. 1

Monitoring for Osmotic Demyelination Syndrome

Watch for signs of osmotic demyelination syndrome typically occurring 2-7 days after rapid correction: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, or altered mental status. 1 Risk factors include correction exceeding 8 mmol/L in 24 hours, liver disease, alcoholism, malnutrition, hypokalemia, and severe baseline hyponatremia. 1, 6