How do you manage a patient with hyponatremia, considering their underlying cause, symptoms, and past medical history, such as heart failure or liver disease?

Management of Hyponatremia

The management of hyponatremia depends critically on three factors: symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and chronicity (acute <48 hours vs. chronic >48 hours), with the overriding principle being that correction must never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

Confirm True Hyponatremia

• Measure serum osmolality to exclude pseudohyponatremia from hyperglycemia (add 1.6 mEq/L to sodium for each 100 mg/dL glucose >100 mg/dL) 1
• Obtain serum and urine osmolality, urine sodium concentration, and urine electrolytes 1
• Assess extracellular fluid volume status through physical examination, looking for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia) or peripheral edema, ascites, jugular venous distention (hypervolemia) 1

Determine Symptom Severity

• Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) require immediate hypertonic saline 1
• Moderate symptoms (nausea, vomiting, confusion, headache) warrant hospital admission with monitored correction 1
• Mild/asymptomatic cases can be managed more conservatively based on etiology 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve, with total correction not exceeding 8 mmol/L in 24 hours. 1

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Monitor serum sodium every 2 hours during initial correction 1
• Once 6 mmol/L is corrected in 6 hours, only 2 mmol/L additional correction is allowed in the next 18 hours 1
• Consider ICU admission for close monitoring 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status and underlying etiology 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts good response to saline (positive predictive value 71-100%) 1
• Continue isotonic saline until euvolemia is achieved 1
• Avoid hypotonic fluids (0.45% saline, D5W) which worsen hyponatremia 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• For persistent cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 2
• Alternative pharmacological options include urea, demeclocycline, or lithium (less commonly used due to side effects) 1
• Rule out hypothyroidism and adrenal insufficiency before confirming SIADH 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1

• 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 ascites and edema 1
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy 1, 2

Critical Correction Rate Guidelines

Standard Correction Rates

• Maximum correction: 8 mmol/L in 24 hours for all patients 1
• Target rate: 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 1
• For severe symptoms: correct 6 mmol/L over first 6 hours, then slow to achieve no more than 8 mmol/L total in 24 hours 1

High-Risk Populations Requiring Slower Correction (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours)

• Advanced liver disease or cirrhosis 1
• Chronic alcoholism 1
• Malnutrition 1
• Prior encephalopathy 1
• Severe hyponatremia (<120 mmol/L) 1
• Hypophosphatemia, hypokalemia, hypoglycemia 1

Special Populations and Considerations

Neurosurgical Patients: Distinguishing SIADH from Cerebral Salt Wasting (CSW)

In neurosurgical patients, cerebral salt wasting is more common than SIADH and requires fundamentally different treatment. 1

SIADH Characteristics

• Euvolemic state (no edema, no orthostatic hypotension, normal skin turgor) 1
• Urine sodium >20-40 mmol/L 1
• Urine osmolality >300 mOsm/kg 1
• Treatment: Fluid restriction to 1 L/day 1

Cerebral Salt Wasting Characteristics

• True hypovolemia with CVP <6 cm H₂O 1
• Urine sodium >20 mmol/L despite volume depletion 1
• Evidence of extracellular volume depletion (hypotension, tachycardia, dry mucous membranes) 1
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• For severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU 1

Critical: Fluid restriction in CSW worsens outcomes and should never be used. 1

Subarachnoid Hemorrhage Patients at Risk of Vasospasm

• Do NOT use fluid restriction 1
• Consider fludrocortisone to prevent vasospasm 1
• Hydrocortisone may prevent natriuresis 1

Cirrhotic Patients

• Hyponatremia in cirrhosis is mostly hypervolemic and dilutional, occurring in ~60% of patients 1
• Serum sodium ≤130 mmol/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Sodium restriction (not fluid restriction) results in weight loss as fluid passively follows sodium 1
• Albumin infusion may improve hyponatremia 1
• Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs. 2% placebo) and should be used with extreme caution 1, 2

Heart Failure Patients

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Continue diuretics for fluid overload even with mild hyponatremia (sodium 126-135 mmol/L) with close electrolyte monitoring 1
• Vasopressin antagonists may be considered for persistent severe hyponatremia despite water restriction and maximization of guideline-directed medical therapy 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately intervene to prevent osmotic demyelination syndrome. 1

• 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
• Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Monitoring Protocols

Severe Symptoms

• Check serum sodium every 2 hours during initial correction phase 1
• After resolution of severe symptoms, check every 4 hours 1

Mild Symptoms or Asymptomatic

• Check sodium every 24 hours initially 1
• Adjust frequency based on response and clinical stability 1

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1
• Using fluid restriction in cerebral salt wasting worsens outcomes 1
• Inadequate monitoring during active correction 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild hyponatremia increases fall risk (21% vs. 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 3
• Using lactated Ringer's solution for hyponatremia treatment (it is hypotonic with sodium 130 mEq/L and can worsen hyponatremia) 1

Pharmacological Interventions

Vasopressin Receptor Antagonists (Vaptans)

Tolvaptan is FDA-approved for euvolemic or hypervolemic hyponatremia, with starting dose of 15 mg once daily, titrating to 30-60 mg based on response. 1, 2

• Significantly increases serum sodium compared to placebo in clinical trials 2
• Use with caution to avoid overly rapid correction (>8 mmol/L/day) 1
• Contraindicated in hypovolemic hyponatremia 1
• In cirrhosis, use with extreme caution due to higher risk of gastrointestinal bleeding and increased all-cause mortality with long-term use 1
• Monitor for side effects: thirst, dry mouth, increased urination 1

Urea

• Effective treatment option for SIADH alongside fluid restriction 1
• Dose: 40 g in 100-150 mL normal saline every 8 hours for neurosurgical patients 1
• Particularly valuable when combined with appropriate volume replacement in cerebral salt wasting 1