Management of Hyponatremia in the ICU
Initial Assessment and Classification
Hyponatremia in the ICU requires immediate systematic evaluation based on symptom severity, volume status, and serum osmolality to guide treatment and prevent life-threatening complications. 1
Step 1: Confirm True Hyponatremia and Assess Severity
- Obtain serum sodium, serum osmolality, and glucose to exclude pseudohyponatremia (hyperproteinemia, hyperlipidemia) and hypertonic hyponatremia (hyperglycemia) 1, 2
- Classify severity: mild (126-135 mEq/L), moderate (120-125 mEq/L), or severe (<120 mEq/L) 1, 3
- Even mild hyponatremia (130-135 mEq/L) should not be ignored as it increases fall risk (21% vs 5%) and mortality (60-fold increase when <130 mEq/L) 1
Step 2: Determine Symptom Severity and Acuity
Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) require immediate hypertonic saline regardless of chronicity. 1, 2
- Severe symptoms: seizures, coma, altered mental status, cardiorespiratory distress 1, 4
- Moderate symptoms: nausea, vomiting, headache, confusion, muscle cramps 1, 3
- Mild/asymptomatic: weakness, gait instability, cognitive impairment 1, 2
- Determine acuity: acute (<48 hours) vs chronic (>48 hours or unknown duration) 1, 4
Step 3: Assess Volume Status
Perform focused physical examination looking for specific signs 1, 5:
- Hypovolemic: orthostatic hypotension, tachycardia, dry mucous membranes, decreased skin turgor, sunken eyes, furrowed tongue 1
- Euvolemic: no edema, normal blood pressure, moist mucous membranes, normal skin turgor 1
- Hypervolemic: jugular venous distention, peripheral edema, ascites, orthopnea, dyspnea 1, 5
Step 4: Obtain Diagnostic Laboratory Tests
- Urine sodium concentration and urine osmolality 1, 2
- Serum creatinine, BUN, potassium, calcium, magnesium 1
- Thyroid-stimulating hormone (TSH) and cortisol if euvolemic 1
- Liver function tests if hypervolemic 1
Treatment Algorithm Based on Symptom Severity
For Severe Symptomatic Hyponatremia (Medical Emergency)
Administer 3% hypertonic saline immediately with 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve. 1, 2
- Target correction: 6 mEq/L over first 6 hours or until severe symptoms resolve 1
- Maximum correction limit: 8 mEq/L in 24 hours to prevent osmotic demyelination syndrome 1, 6, 2
- Monitor serum sodium every 2 hours during initial correction 1
- Require ICU admission for close monitoring 1, 4
- After symptom resolution, monitor sodium every 4 hours 1
For 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, 7
- Urine sodium <30 mmol/L predicts response to saline with 71-100% positive predictive value 1
- Once euvolemic, reassess sodium levels 1
- Correction rate should not exceed 8 mEq/L in 24 hours 1
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 2
- Implement strict fluid restriction to 1000 mL/day 1, 3
- 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 (40 g every 8 hours in 100-150 mL normal saline) or demeclocycline 1
- Vasopressin receptor antagonists (tolvaptan 15 mg daily, titrate to 30-60 mg) may be used for resistant cases 1, 6
- Tolvaptan must be initiated in hospital with close sodium monitoring due to risk of overly rapid correction 6
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for sodium <125 mEq/L and avoid hypertonic saline unless life-threatening symptoms present. 1, 7
- Fluid restriction to 1000-1500 mL/day 1, 3
- Temporarily discontinue diuretics if sodium <125 mEq/L 1
- In cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) alongside fluid restriction 1
- Sodium restriction (2000 mg/day or 88 mmol/day) is more effective than fluid restriction for weight loss 1
- Vasopressin antagonists may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to 10% risk of GI bleeding vs 2% with placebo 1
Special Considerations for Neurosurgical Patients
In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW) as treatment approaches are fundamentally opposite. 1
Cerebral Salt Wasting (More Common in Neurosurgical Patients)
- CSW requires volume and sodium replacement, NOT fluid restriction 1
- Evidence of volume depletion: hypotension, tachycardia, dry mucous membranes 1
- Urine sodium typically >20 mmol/L with high urine osmolality 1
- Treatment: isotonic or hypertonic saline based on severity 1
- Consider fludrocortisone (0.1-0.2 mg daily) or hydrocortisone to reduce natriuresis 1
- Fluid restriction in CSW worsens outcomes 1
Subarachnoid Hemorrhage Patients
- Do NOT use fluid restriction in patients at risk for vasospasm 1
- Maintain adequate volume status to prevent cerebral ischemia 1
- Hypertonic saline increases regional cerebral blood flow and brain tissue oxygen 1
Correction Rate Guidelines and Osmotic Demyelination Prevention
The single most critical safety principle: never exceed 8 mEq/L correction in 24 hours for chronic hyponatremia. 1, 6, 2
Standard Correction Rates
- Maximum correction: 8 mEq/L in 24 hours for average-risk patients 1, 2
- Target rate: 4-6 mEq/L per day for safer correction 1
- For severe symptoms: 6 mEq/L over first 6 hours, then slow correction 1
High-Risk Patients Requiring Slower Correction (4-6 mEq/L per day)
- Advanced liver disease or cirrhosis 1, 6
- Chronic alcoholism 1, 6
- Severe malnutrition 1, 6
- Hypokalemia, hypophosphatemia, hypoglycemia 1
- Prior history of encephalopathy 1
- Baseline sodium <120 mEq/L 1
Management of Overcorrection
If sodium correction exceeds 8 mEq/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1
- Administer desmopressin to slow or reverse the rapid rise 1
- Target reduction to bring total 24-hour correction to no more than 8 mEq/L from starting point 1
- Monitor for osmotic demyelination syndrome symptoms (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1, 6
Monitoring Requirements in ICU
During Active Correction
- Severe symptoms: monitor sodium every 2 hours initially 1
- After symptom resolution: monitor every 4 hours 1
- Asymptomatic/mild symptoms: monitor daily 1, 3
- Monitor neurologic status continuously for signs of worsening cerebral edema or osmotic demyelination 1, 4
- Track urine output, fluid balance, and volume status 1
After Stabilization
- Continue daily sodium monitoring until stable 1, 3
- Monitor for recurrence after discontinuing treatment 1
- Educate patient on fluid restriction compliance 1
Critical Pitfalls to Avoid
- Overly rapid correction exceeding 8 mEq/L in 24 hours causes osmotic demyelination syndrome 1, 6, 2
- Using fluid restriction in cerebral salt wasting worsens outcomes 1
- Administering hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens edema and ascites 1
- Inadequate monitoring during active correction 1
- Failing to identify and treat the underlying cause 1, 5
- Ignoring mild hyponatremia (130-135 mEq/L) as clinically insignificant 1
- Using normal saline in SIADH (worsens hyponatremia) 1
- Administering hypotonic fluids in any hyponatremia (worsens condition) 1
Special Population Considerations
Cirrhotic Patients
- Higher risk of complications: spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), hepatic encephalopathy (OR 2.36) 1
- Require more cautious correction (4-6 mEq/L per day) 1
- Albumin infusion beneficial alongside fluid restriction 1
- Avoid tolvaptan due to 10% GI bleeding risk vs 2% placebo 1
- Hyponatremia reflects worsening hemodynamic status 1