What is the approach to managing hyponatremia?

Approach to Hyponatremia

Begin by confirming true hypotonic hyponatremia (serum osmolality <275 mOsm/kg), then immediately assess volume status and symptom severity to guide treatment—this determines whether you give saline, restrict fluids, or administer hypertonic saline. 1, 2

Initial Diagnostic Workup

Confirm the diagnosis and exclude pseudohyponatremia:

• Correct sodium for hyperglycemia: add 1.6 mEq/L to measured sodium for each 100 mg/dL glucose above 100 mg/dL 2, 3
• Check serum osmolality to confirm hypotonic hyponatremia (<275 mOsm/kg) 1, 2
• Obtain urine osmolality, urine sodium, serum creatinine, TSH, and cortisol 1, 2

Assess volume status through physical examination:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1, 4
• Euvolemic signs: normal blood pressure, no edema, moist mucous membranes 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1, 5

Interpret urine studies:

• Urine sodium <30 mmol/L suggests hypovolemic hyponatremia (71-100% positive predictive value for saline responsiveness) 1
• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH 1, 6
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, altered mental status, or cardiorespiratory distress, immediately administer 3% hypertonic saline—this is a medical emergency requiring ICU-level monitoring. 1, 2, 3

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 2, 7
• Target correction of 6 mmol/L over first 6 hours or until severe symptoms resolve 1, 2, 6
• Never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3
• Monitor serum sodium every 2 hours during initial correction 1, 2

Mild to Moderate Hyponatremia (Asymptomatic or Mild Symptoms)

Treatment depends entirely on volume status:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion. 1, 2, 5

• 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 1
• Once euvolemic, reassess and adjust management based on sodium response 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 2, 6

• 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, 8
• Alternative options include urea, demeclocycline, or lithium (less commonly used due to side effects) 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L and treat the underlying condition. 1, 2, 5

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1, 2
• Avoid hypertonic saline unless life-threatening symptoms are present—it worsens ascites and edema 1
• Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1, 8

Critical Correction Rate Guidelines

The single most important safety principle: never exceed 8 mmol/L correction in 24 hours. 1, 2, 3

Standard correction rates:

• Average risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 2

Monitoring frequency:

• Severe symptoms: every 2 hours during initial correction 1, 2
• Mild symptoms: every 4 hours after symptom resolution 2
• Chronic management: daily until target sodium achieved 2

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, this is an emergency requiring immediate intervention to prevent osmotic demyelination syndrome. 1

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1, 2
• Consider administering desmopressin to slow or reverse the rapid rise 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Special Considerations in Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW)—they require opposite treatments. 1, 4

SIADH characteristics:

• Euvolemic state, urine sodium >20-40 mmol/L, 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, urine sodium >20 mmol/L despite volume depletion 1
• Treatment: volume and sodium replacement with isotonic or hypertonic saline, never fluid restriction 1, 4
• For severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1

In subarachnoid hemorrhage patients at risk of vasospasm:

• Never use fluid restriction—it worsens outcomes 1
• Consider fludrocortisone or hydrocortisone to prevent natriuresis 1

Common Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 3
• Never use fluid restriction in cerebral salt wasting—it worsens outcomes 1
• Never ignore mild hyponatremia (130-135 mmol/L)—it increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 3
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
• Inadequate monitoring during active correction leads to overcorrection 1
• Failing to identify and treat the underlying cause perpetuates the problem 1

Treatment Algorithm by Sodium Level

Sodium 126-135 mmol/L:

• Continue diuretic therapy with close electrolyte monitoring 2
• No water restriction needed at this level 1
• Consider underlying causes and monitor for progression 1

Sodium 121-125 mmol/L:

• More cautious approach warranted 1
• Implement fluid restriction to 1-1.5 L/day for hypervolemic patients 1
• Consider discontinuing diuretics 1

Sodium ≤120 mmol/L:

• Stop diuretics immediately 2
• Severe fluid restriction plus albumin infusion (hypervolemic) or volume expansion (hypovolemic) 2
• Consider hypertonic saline only if severe symptoms present 1