What is the approach to managing hyponatremia in the Intensive Care Unit (ICU)?

Hyponatremia Workup in the ICU

Initial Assessment and Classification

Begin by determining the severity and acuity of hyponatremia, as this dictates the urgency and aggressiveness of treatment. 1

Immediate Laboratory Evaluation

• Obtain serum sodium, serum osmolality, urine osmolality, urine sodium concentration, and uric acid levels 1
• Check serum creatinine, blood urea nitrogen, glucose, thyroid-stimulating hormone, and cortisol to rule out secondary causes 1
• Measure serum potassium, calcium, and magnesium 1
• Do NOT obtain ADH or natriuretic peptide levels—these are not supported by evidence and delay treatment 1

Volume Status Assessment

• Assess extracellular fluid volume status through physical examination 1:
  • Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia 1
  • Euvolemic signs: no edema, normal blood pressure, moist mucous membranes 1
  • Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1

Severity Classification

• Mild: 130-135 mmol/L 1
• Moderate: 120-129 mmol/L 1
• Severe: <120 mmol/L 1

Symptom Assessment

• Severe symptoms (requiring immediate treatment): seizures, coma, altered mental status, cardiorespiratory distress 2, 3
• Moderate symptoms: nausea, vomiting, headache, confusion 1
• Mild/asymptomatic: weakness, fatigue, or no symptoms 1

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Emergency Management for Severe Symptomatic Hyponatremia

If the patient has seizures, coma, or severe neurological symptoms, immediately administer 100 mL of 3% hypertonic saline IV over 10 minutes. 2

Acute Treatment Protocol

• Give 100 mL boluses of 3% hypertonic saline over 10 minutes, repeating every 10 minutes if seizures persist, up to three total boluses 2
• Target an initial sodium increase of 4-6 mEq/L in the first hour or until severe symptoms resolve 2, 3
• Maximum correction limit: 6 mmol/L over 6 hours, then only 2 mmol/L in the following 18 hours, with a total maximum of 8 mmol/L in 24 hours 1, 2, 4

ICU Monitoring During Acute Correction

• Check serum sodium every 2 hours during initial correction 1, 2
• Monitor strict intake and output 2
• Obtain daily weights 2
• Watch for signs of osmotic demyelination syndrome: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis (typically occurs 2-7 days after rapid correction) 1, 4

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Management Based on Volume Status

Hypovolemic Hyponatremia

Diagnostic criteria: Urine sodium <30 mmol/L, signs of volume depletion 1

• Discontinue diuretics immediately 1
• Administer isotonic (0.9%) saline for volume repletion 1
• Once euvolemic, reassess and adjust therapy based on sodium response 1
• Do NOT use vaptans—these are contraindicated in hypovolemic states 1

Euvolemic Hyponatremia (SIADH)

Diagnostic criteria: Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg, euvolemic on exam 1

For Mild-Moderate Symptoms or Asymptomatic:

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2
• If no response after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider urea 30-60 g/day (effective and inexpensive in ICU setting) 5 or demeclocycline 1

For Severe Symptoms:

• Use 3% hypertonic saline as described above 2
• Transition to fluid restriction once symptoms resolve 2

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Diagnostic criteria: Peripheral edema, ascites, jugular venous distention 1

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens fluid overload 1
• Vaptans (tolvaptan 15 mg daily) may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to increased risk of gastrointestinal bleeding (10% vs 2% placebo) 1, 4

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Special ICU Considerations

Cerebral Salt Wasting (Common in Neurosurgical Patients)

Diagnostic criteria: Hypovolemia with high urine sodium >20 mmol/L, often in setting of subarachnoid hemorrhage or brain injury 1, 2

• Treatment is fundamentally different from SIADH: volume and sodium replacement, NOT fluid restriction 1, 2
• Use isotonic or hypertonic saline based on severity 1
• For severe symptoms, administer 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1, 2
• Consider hydrocortisone to prevent natriuresis in subarachnoid hemorrhage patients 1
• Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1, 2

Patients with Advanced Liver Disease, Alcoholism, or Malnutrition

• These patients require slower correction rates: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 4
• They are at significantly higher risk for osmotic demyelination syndrome 1, 4

Patients Requiring CRRT

• For severe hyponatremia in patients requiring continuous renal replacement therapy, use customized hypotonic dialysate/replacement fluid solutions to achieve gradual correction 6
• Target correction rate of 4-6 mmol/L per day in this high-risk population 6

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Critical Safety Considerations

Prevention of Osmotic Demyelination Syndrome

The most important principle: never exceed 8 mmol/L correction in 24 hours for chronic hyponatremia. 1, 2, 4

• For high-risk patients (cirrhosis, alcoholism, malnutrition, severe hyponatremia <120 mmol/L), limit to 4-6 mmol/L per day 1, 4
• If overcorrection occurs (>8 mmol/L in 24 hours), immediately discontinue current fluids and switch to D5W 1
• Consider administering desmopressin to slow or reverse the rapid rise 1

Monitoring Frequency

• Severe symptoms: Check sodium every 2 hours during initial correction 1, 2
• Moderate symptoms: Check sodium every 4 hours 1
• After stabilization: Check sodium every 6-12 hours until target reached 1

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Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L): Even mild hyponatremia increases fall risk (21% vs 5%), fractures, and mortality 1, 3
• Using normal saline in SIADH: This worsens hyponatremia—use fluid restriction instead 1
• Using fluid restriction in cerebral salt wasting: This is harmful—use volume replacement 1, 2
• Overly rapid correction: Exceeding 8 mmol/L in 24 hours risks osmotic demyelination syndrome 1, 2, 4
• Inadequate monitoring during active correction: Failure to check sodium frequently leads to overcorrection 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms: This worsens edema and ascites 1
• Failing to distinguish SIADH from cerebral salt wasting in neurosurgical patients: These require opposite treatments 1, 2