How to approach a patient with hyponatremia (low sodium level)?

Approach to Hyponatremia

Initial Assessment and Classification

Hyponatremia (serum sodium <135 mmol/L) requires immediate evaluation based on symptom severity, volume status, and serum osmolality to guide treatment and prevent complications. 1

Step 1: Determine Symptom Severity

• Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) require immediate hypertonic saline—this is a medical emergency 1, 2
• Moderate symptoms (nausea, vomiting, confusion, headache, gait instability) warrant hospital admission with monitored correction 1
• Mild/asymptomatic cases allow for outpatient management with underlying cause treatment 1

Step 2: Obtain Essential Laboratory Studies

• Serum osmolality, urine osmolality, and urine sodium concentration 1, 3
• Serum creatinine, glucose, TSH, and cortisol to exclude pseudohyponatremia and endocrine causes 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1, 3
• Do NOT order plasma ADH or natriuretic peptide levels—these are not supported by evidence and delay diagnosis 1, 3

Step 3: Assess Volume Status

Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%), so combine clinical findings with laboratory data 1, 3:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, urine sodium <30 mmol/L (extrarenal losses) or >20 mmol/L (renal losses) 1, 3
• Euvolemic signs: normal volume status, no edema, urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg suggests SIADH 1, 3
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1, 3

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. 1

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to 3 times at 10-minute intervals 1
• Maximum correction: 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 4, 2
• Monitor serum sodium every 2 hours during initial correction 1
• For high-risk patients (cirrhosis, alcoholism, malnutrition, severe hyponatremia), limit correction to 4-6 mmol/L per day 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia

• Discontinue diuretics immediately if sodium <125 mmol/L 1
• Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts 71-100% response to saline infusion 1, 3
• For cirrhotic patients, consider albumin infusion alongside isotonic saline 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• For severe symptoms or sodium <120 mEq/L, use 3% hypertonic saline with careful monitoring 1, 3
• Consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) for resistant cases 1, 4
• Tolvaptan must be initiated in hospital with close sodium monitoring due to risk of overly rapid correction 4

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Temporarily discontinue diuretics until sodium improves 1
• For cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) 1
• Avoid hypertonic saline unless life-threatening symptoms present—it worsens ascites and edema 1
• Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss, as fluid follows sodium 1

Special Populations and Critical Distinctions

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting (CSW)

Distinguishing these conditions is critical because they require opposite treatments. 1, 3, 5

SIADH characteristics:

• Euvolemic state (CVP 6-10 cm H₂O) 1, 5
• Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg 1, 3
• Treatment: fluid restriction to 1 L/day 1, 5

CSW characteristics:

• Hypovolemic state (CVP <6 cm H₂O) with clinical volume depletion 1, 5
• Urine sodium >20 mmol/L despite volume depletion 1, 5
• Treatment: volume and sodium replacement with isotonic or hypertonic saline, fludrocortisone 0.1-0.2 mg daily for severe cases 1, 5
• Never use fluid restriction in CSW—this worsens outcomes 1, 5

Subarachnoid Hemorrhage Patients

• Never use fluid restriction in patients at risk of vasospasm 1
• Consider fludrocortisone 0.1-0.2 mg daily to prevent vasospasm 1
• Hydrocortisone may prevent natriuresis 1

Cirrhotic Patients

• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Sodium <130 mmol/L associated with 60-fold increased mortality (11.2% vs 0.19%) 1
• Maximum correction 4-6 mmol/L per day, never exceeding 8 mmol/L in 24 hours due to high osmotic demyelination risk 1
• Tolvaptan carries higher gastrointestinal bleeding risk in cirrhosis (10% vs 2% placebo) 1

Critical Safety Considerations and Common Pitfalls

Osmotic Demyelination Syndrome Prevention

• Never exceed 8 mmol/L correction in 24 hours for chronic hyponatremia 1, 4, 2
• High-risk patients require even slower correction (4-6 mmol/L per day): advanced liver disease, alcoholism, malnutrition, severe hyponatremia (<120 mmol/L) 1
• If overcorrection occurs, immediately discontinue current fluids, switch to D5W, and consider desmopressin 1
• Watch for osmotic demyelination signs 2-7 days post-correction: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1, 4

Common Pitfalls to Avoid

• Using fluid restriction in CSW worsens outcomes—CSW requires volume replacement 1, 5
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild hyponatremia increases fall risk (21% vs 5%) and mortality 1, 2
• Inadequate monitoring during active correction—check sodium every 2 hours for severe symptoms, every 4 hours for mild symptoms 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload 1
• Failing to recognize and treat the underlying cause leads to recurrence 1
• Stopping diuretics prematurely in volume-overloaded heart failure patients due to mild hyponatremia—persistent volume overload is more dangerous 1

Monitoring Requirements

• Severe symptoms: sodium every 2 hours during initial correction 1
• Mild symptoms: sodium every 4 hours initially, then daily 1
• Chronic hyponatremia: sodium every 24-48 hours to ensure safe correction rate 1

Pharmacological Options Summary

• 3% hypertonic saline: severe symptomatic hyponatremia only, 100 mL boluses over 10 minutes 1, 6
• Isotonic saline (0.9% NaCl): hypovolemic hyponatremia for volume repletion 1
• Tolvaptan: euvolemic/hypervolemic hyponatremia resistant to fluid restriction, 15 mg daily titrated to 60 mg, hospital initiation required, limit use to 30 days 1, 4
• Fludrocortisone: CSW in neurosurgical patients, 0.1-0.2 mg daily 1, 5
• Oral sodium chloride: SIADH refractory to fluid restriction, 100 mEq three times daily 1