What is the recommended approach for correcting sodium imbalance in a patient with severe hyponatremia or hypernatremia?

Sodium Correction in Hyponatremia and Hypernatremia

Hyponatremia Correction

The maximum correction rate for hyponatremia must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome, with high-risk patients (advanced liver disease, alcoholism, malnutrition) requiring even slower correction at 4-6 mmol/L per day. 1

Initial Assessment and Classification

• Determine acuity: acute (<48 hours) versus chronic (>48 hours) hyponatremia, as this fundamentally changes correction rates 1
• Assess volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemic); peripheral edema, ascites, jugular venous distention (hypervolemic); or absence of these findings (euvolemic) 1
• Obtain serum and urine osmolality, urine sodium, and urine electrolytes to determine underlying etiology 1
• Classify symptom severity: severe symptoms (seizures, coma, altered mental status) require immediate intervention; mild symptoms (nausea, headache, weakness) allow more measured approach 1, 2

Correction Rates Based on Symptom Severity

For severe symptomatic hyponatremia (seizures, coma, confusion):

• Administer 3% hypertonic saline immediately with target correction of 6 mmol/L over first 6 hours or until severe symptoms resolve 1, 3
• After initial 6 mmol/L correction, limit additional correction to only 2 mmol/L in the following 18 hours 3
• Total correction must not exceed 8 mmol/L in 24 hours 1, 3
• Monitor serum sodium every 2 hours during initial correction phase 1
• Discontinue 3% saline when severe symptoms resolve and transition to protocols for mild symptoms 3

For mild symptoms or asymptomatic hyponatremia:

• Correction rate of 4-8 mmol/L per day for average-risk patients, not exceeding 10-12 mmol/L in 24 hours 1
• For high-risk patients (cirrhosis, alcoholism, malnutrition, severe hyponatremia, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• Monitor serum sodium every 4 hours initially, then daily 1

Treatment Based on Volume Status

Hypovolemic hyponatremia:

• Discontinue diuretics immediately 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 good response to saline infusion (positive predictive value 71-100%) 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 resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 4
• Avoid fluid restriction during first 24 hours of tolvaptan therapy 4

Hypervolemic hyponatremia (heart failure, cirrhosis):

• Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1

Special Populations

Neurosurgical patients:

• Distinguish between SIADH and cerebral salt wasting (CSW), as treatments are opposite 1
• CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• For severe CSW symptoms, use 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Cirrhotic patients:

• Maximum correction 4-6 mmol/L per day due to extremely high risk of osmotic demyelination syndrome 1
• Sodium restriction (not fluid restriction) results in weight loss, as fluid follows sodium 1
• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse rapid rise in serum sodium 1
• Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point 1

Critical Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 4
• Never use fluid restriction in cerebral salt wasting—this 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, 2, 5
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Inadequate monitoring during active correction leads to osmotic demyelination syndrome 1

Hypernatremia Correction

For hypernatremia, use hypotonic fluids with maximum correction rate of 0.4 mmol/L/hour or 10 mmol/L per 24 hours to prevent cerebral edema. 1, 6

Fluid Selection

• Primary choice: 5% dextrose (D5W) as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 1
• Alternative: 0.45% NaCl (half-normal saline, 77 mEq/L sodium) for moderate hypernatremia 1
• For more aggressive free water replacement: 0.18% NaCl (quarter-normal saline, 31 mEq/L sodium) 1
• Never use isotonic saline (0.9% NaCl) in hypernatremia—it worsens the condition by delivering excessive osmotic load 1

Correction Rates

• Maximum rate: 0.4 mmol/L/hour or 10 mmol/L per 24 hours 1, 6
• For acute hypernatremia (<48 hours): rapid correction improves prognosis by preventing cellular dehydration 6
• For chronic hypernatremia (>days): slow correction rate (no more than 0.4 mmol/L/hour) is mandatory 6
• Correction rates faster than 48-72 hours for severe hypernatremia increase risk of pontine myelinolysis 1

Initial Fluid Administration Rates

• Children: 100 mL/kg/24 hours for first 10 kg, 50 mL/kg/24 hours for 10-20 kg, 20 mL/kg/24 hours for remaining weight 1
• Adults: 25-30 mL/kg/24 hours 1

Special Considerations

• Patients with nephrogenic diabetes insipidus require ongoing hypotonic fluid administration to match excessive free water losses 1
• Address underlying causes: replace ongoing losses from diarrhea/vomiting, ensure access to free water for inadequate intake 1