What is the initial approach to managing hyponatremia?

Approach to Hyponatremia

Initial Assessment and Classification

Begin by determining the patient's volume status (hypovolemic, euvolemic, or hypervolemic) through physical examination, then obtain serum and urine osmolality, urine sodium, and urine electrolytes to guide treatment. 1

• Check for orthostatic hypotension, dry mucous membranes, poor skin turgor (hypovolemia), jugular venous distention, peripheral edema, ascites (hypervolemia), or absence of these findings (euvolemia) 1
• Measure serum osmolality to rule out pseudohyponatremia (normal osmolality) or hyperglycemia-induced hyponatremia (high osmolality) 2
• Obtain urine sodium concentration: <30 mmol/L suggests hypovolemia with 71-100% positive predictive value for response to saline; >20 mmol/L with high urine osmolality (>500 mOsm/kg) suggests SIADH 1, 3
• Assess symptom severity: mild (nausea, headache, weakness), moderate (confusion, disorientation), or severe (seizures, coma, altered consciousness) 4
• Determine acuity: acute (<48 hours) versus chronic (>48 hours), as this critically affects correction rates 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve, but never exceed 8 mmol/L total correction in 24 hours. 1, 5

• Give 100-150 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 6
• Monitor serum sodium every 2 hours during initial correction 1
• Consider ICU admission for close monitoring 1
• The maximum correction limit is 8 mmol/L in 24 hours for most patients, or 4-6 mmol/L per day for high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy) to prevent osmotic demyelination syndrome 1, 7

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends entirely on volume status:

Hypovolemic Hyponatremia

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1
• Once euvolemic, reassess and adjust treatment based on sodium response 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of first-line treatment 1, 5
• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider urea (effective and safe second-line option) or vaptans (tolvaptan 15 mg daily, titrate to 30-60 mg) 1, 5, 6
• Demeclocycline and lithium are less commonly used due to side effects 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 4
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1
• Vaptans may be considered for persistent severe hyponatremia despite fluid restriction and optimization of guideline-directed therapy, but use with extreme caution in cirrhosis due to increased gastrointestinal bleeding risk (10% vs 2% placebo) 1, 7

Special Populations and Critical Considerations

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches are fundamentally opposite 1
• CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• For severe CSW symptoms, use 3% hypertonic saline plus fludrocortisone in ICU 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
• Consider fludrocortisone or hydrocortisone to prevent natriuresis 1

Cirrhotic Patients

• Require more cautious correction rates: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Sodium restriction (not fluid restriction) results in weight loss, as fluid follows sodium 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), and consider administering desmopressin to reverse the rapid rise. 1

• Monitor for osmotic demyelination syndrome signs: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, typically occurring 2-7 days after rapid correction 1, 7
• Target relowering to bring total 24-hour correction to no more than 8 mmol/L from baseline 1

Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild hyponatremia increases fall risk (21% vs 5%) and mortality 1, 5
• Using fluid restriction in cerebral salt wasting, which worsens outcomes 1
• Inadequate monitoring during active correction 1
• Failing to identify and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Overly rapid correction exceeding 8 mmol/L in 24 hours, risking osmotic demyelination syndrome 1, 7