What is the recommended initial replacement therapy for a patient with hyponatremia, including how to manage symptomatic (confusion, seizures, severe nausea/vomiting, headache, coma) versus asymptomatic cases and appropriate correction limits?

Replacement Therapy for Hyponatremia

Immediate Management Based on Symptom Severity

For severe symptomatic hyponatremia (confusion, seizures, coma), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, never exceeding 8 mmol/L total correction in 24 hours. 1, 2

Severe Symptomatic Cases (Seizures, Coma, Altered Mental Status)

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until severe symptoms improve 1
• Target initial correction of 6 mmol/L within the first 6 hours 1, 2, 3
• Critical safety limit: total correction must not exceed 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome 1, 2, 3
• Monitor serum sodium every 2 hours during active correction 1
• Consider ICU admission for continuous monitoring 1

Asymptomatic or Mildly Symptomatic Cases

Treatment depends entirely on volume status—hypovolemic, euvolemic, or hypervolemic hyponatremia require fundamentally different approaches. 1, 4, 3

Hypovolemic Hyponatremia

• 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
• Discontinue any contributing diuretics immediately 1, 4
• Urine sodium <30 mmol/L predicts good response to saline with 71-100% positive predictive value 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2, 4, 3
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1, 2
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 3
• Alternative options include urea, demeclocycline, or lithium for refractory cases 1, 5

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 4, 3
• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• For cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1

Correction Rate Guidelines: The Most Critical Safety Consideration

The maximum correction rate of 8 mmol/L in 24 hours is non-negotiable for chronic hyponatremia (>48 hours duration). 1, 2, 4, 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 require even slower correction: 4-6 mmol/L per day, absolute maximum 8 mmol/L in 24 hours 1, 2

High-Risk Populations Requiring Slower Correction

• Advanced liver disease or cirrhosis 1, 2
• Chronic alcoholism 1, 2
• Malnutrition 1, 2
• Prior encephalopathy 1
• Severe hyponatremia (<120 mmol/L) 1
• Hypokalemia, hypophosphatemia, or hypoglycemia 1

Acute vs. Chronic Hyponatremia

• Acute hyponatremia (<48 hours) can be corrected more rapidly (up to 1 mmol/L/hour) without risk of osmotic demyelination 1, 6
• Chronic hyponatremia (>48 hours) requires strict adherence to the 8 mmol/L/24-hour limit 1, 3

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguishing cerebral salt wasting (CSW) from SIADH is critical because they require opposite treatments. 1

Cerebral Salt Wasting (CSW)

• Treat with volume and sodium replacement using isotonic or hypertonic saline, never fluid restriction 1, 2
• For severe symptoms, use 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU setting 1
• Consider hydrocortisone to prevent natriuresis in subarachnoid hemorrhage patients 1
• Fluid restriction in CSW worsens outcomes and should never be used 1
• In subarachnoid hemorrhage patients at risk of vasospasm, avoid fluid restriction entirely 1

Distinguishing CSW from SIADH

• CSW: true hypovolemia with CVP <6 cm H₂O, orthostatic hypotension, dry mucous membranes 1
• SIADH: euvolemic state with normal to slightly elevated CVP 1
• Both have urine sodium >20 mmol/L, but CSW shows volume depletion despite high urine sodium 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, this is a medical emergency requiring immediate intervention. 1

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Administer desmopressin to slow or reverse the rapid sodium rise 1, 7
• Target relowering to bring total 24-hour correction back to ≤8 mmol/L from starting point 1
• Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Monitoring Protocol

Severe Symptomatic Cases

• Check serum sodium every 2 hours during initial correction phase 1, 2
• After symptom resolution, check every 4 hours 1

Mild Symptoms or Asymptomatic

• Check serum sodium every 4-6 hours during initial correction 2
• Once stable, transition to every 24-48 hours 1

Common Pitfalls to Avoid

• Never use fluid restriction as initial treatment for altered mental status from hyponatremia—this requires hypertonic saline 1
• Never exceed 8 mmol/L correction in 24 hours for chronic hyponatremia 1, 2, 3
• Never use fluid restriction in cerebral salt wasting or subarachnoid hemorrhage patients at risk of vasospasm 1
• Never ignore mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk 21% vs 5% and mortality 60-fold 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Never fail to distinguish between hypovolemic, euvolemic, and hypervolemic states before initiating treatment 1, 4, 3
• Never administer hypotonic fluids (lactated Ringer's, 0.45% saline) to patients with hyponatremia—this worsens the condition 1