How should hyponatremia be managed and corrected based on its acuity, symptom severity, and volume status while avoiding overcorrection?

Sodium Correction in Hyponatremia

The rate of sodium correction must be tailored to symptom severity and chronicity, with a maximum increase of 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome, while severe symptomatic cases require immediate hypertonic saline targeting 6 mmol/L correction over 6 hours. 1

Classification by Acuity and Symptom Severity

Acute vs. Chronic Hyponatremia

• Acute hyponatremia is defined as onset <48 hours or when sodium decreases >0.5 mmol/L/hour, typically from rapid fluid administration in the setting of impaired water excretion 2
• Chronic hyponatremia (>48 hours or unknown duration) carries higher risk of osmotic demyelination with rapid correction and requires more cautious management 1, 3
• The rapidity of development determines symptom severity more than the absolute sodium level—acute drops cause more severe symptoms at the same sodium concentration 4, 5

Symptom Classification

• Severe symptoms include altered consciousness, seizures, coma, somnolence, obtundation, or cardiorespiratory distress—these constitute a medical emergency 6, 5
• Moderate symptoms encompass nausea, vomiting, confusion, headache, muscle cramps, and gait instability 4
• Mild or asymptomatic patients may have only subtle cognitive impairment, weakness, or no symptoms despite sodium 120-135 mmol/L 4, 5

Correction Rate Guidelines

Standard Correction Limits

• Maximum correction: 8 mmol/L in any 24-hour period for all patients to prevent osmotic demyelination syndrome 1, 6, 5
• Target correction rate of 4-8 mmol/L per day for standard-risk patients, never exceeding 10-12 mmol/L in 24 hours 1
• If 6 mmol/L is corrected in the first 6 hours for severe symptoms, only 2 mmol/L additional correction is allowed in the next 18 hours 6

High-Risk Populations Requiring Slower Correction

• Patients with advanced liver disease, chronic alcoholism, malnutrition, or prior hepatic encephalopathy require 4-6 mmol/L per day maximum, with absolute ceiling of 8 mmol/L in 24 hours 1, 6
• Cirrhotic patients have 0.5-1.5% risk of osmotic demyelination even with careful correction 1
• These populations are exceptionally vulnerable to pontine myelinolysis with overcorrection 1, 5

Management Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

• Administer 100 mL of 3% hypertonic saline IV over 10 minutes immediately 6, 5
• Repeat 100 mL bolus every 10 minutes if symptoms persist, up to three total boluses 6
• Target correction of 6 mmol/L over first 6 hours or until severe symptoms resolve 1, 6
• Check serum sodium every 2 hours during initial correction phase 1, 6
• This approach exceeds the 24-hour correction limit in 4.5-28% of cases but is necessary to prevent death from cerebral edema 5

Moderate Symptomatic Hyponatremia

• Use 3% hypertonic saline with target correction of 4-6 mmol/L in first 6 hours 1
• Monitor sodium every 4 hours after symptom resolution 1
• Total correction must not exceed 8 mmol/L in 24 hours 1

Asymptomatic or Mild Chronic Hyponatremia

• Fluid restriction to 1-1.5 L/day is first-line therapy for euvolemic and hypervolemic patients 1, 7
• Adequate solute intake (salt and protein) with initial fluid restriction of 500 mL/day adjusted to sodium levels 7
• Correction rate should be <0.5 mmol/L/hour for chronic cases 2, 3
• Close monitoring alone may be sufficient for asymptomatic patients 3

Management 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/hour, then 4-14 mL/kg/hour based on response 1
• Urine sodium <30 mmol/L predicts good response to saline (positive predictive value 71-100%) 1
• Correction rate still must not exceed 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is cornerstone of treatment 1, 6
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1, 6
• For severe symptoms, use 3% hypertonic saline as above 6
• Nearly half of SIADH patients do not respond to fluid restriction as first-line therapy 7
• Second-line options include urea or tolvaptan 7

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients (8 g per liter of ascites removed) 1
• Avoid hypertonic saline unless life-threatening symptoms present—it worsens ascites and edema 1
• Sodium restriction (not fluid restriction) results in weight loss as fluid follows sodium 1

Special Considerations for Neurosurgical Patients

Distinguishing SIADH from Cerebral Salt Wasting (CSW)

• Volume status is the decisive discriminator: SIADH is euvolemic, CSW is hypovolemic 1, 6
• SIADH: normal to slightly elevated CVP, urine sodium >20-40 mmol/L, treat with fluid restriction 1
• CSW: low CVP (<6 cm H₂O), orthostatic hypotension, dry mucous membranes, urine sodium >20 mmol/L despite volume depletion, treat with volume and sodium replacement 1, 6

Treatment of Cerebral Salt Wasting

• Aggressive volume and sodium replacement with isotonic or hypertonic saline—fluid restriction is contraindicated and worsens outcomes 1, 6
• For severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU 1, 6
• Hydrocortisone may prevent natriuresis in subarachnoid hemorrhage patients 1

Subarachnoid Hemorrhage Patients at Risk of Vasospasm

• Never use fluid restriction—it increases risk of cerebral ischemia 1, 6
• Consider fludrocortisone to prevent vasospasm 1
• Volume expansion is preferred even when volume status is uncertain 1

Monitoring During Correction

Frequency of Sodium Checks

• Severe symptoms: every 2 hours during initial correction 1, 6
• After symptom resolution: every 4 hours 1
• Asymptomatic patients: every 24-48 hours initially 1

Additional Monitoring

• Strict intake and output measurement 6
• Daily weights 6
• Neurological examination for signs of osmotic demyelination syndrome 1, 6
• Serum osmolality, urine osmolality, and urine sodium to guide ongoing therapy 1

Management of Overcorrection

Recognition and Intervention

• If sodium rises >8 mmol/L in 24 hours, immediately discontinue hypertonic saline and switch to D5W (5% dextrose in water) 1
• Administer desmopressin to slow or reverse the rapid rise 1
• Target is to bring total 24-hour correction back to ≤8 mmol/L from baseline 1

Signs of Osmotic Demyelination Syndrome

• Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1, 6
• Symptoms typically appear 2-7 days after rapid correction 1, 6
• Parkinsonism, quadriparesis, or death in severe cases 5

Calculating Sodium Deficit

• Formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
• This helps determine appropriate amount of sodium supplementation needed 1
• Remember this assumes stable fluid balance—adjust for ongoing losses or gains 1

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours—the single most important error leading to osmotic demyelination 1, 6
• Using fluid restriction in cerebral salt wasting worsens outcomes and can be fatal 1, 6
• Inadequate monitoring during active correction 1
• Failing to recognize and treat the underlying cause leads to recurrence 1, 6
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild chronic hyponatremia increases mortality 60-fold and fall risk from 5% to 21% 1, 4
• Applying the same correction rate to high-risk patients (cirrhosis, alcoholism, malnutrition) as standard patients 1, 6