What is the initial approach to treating hyponatremia?

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia must be determined by assessing symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and serum osmolality, with immediate hypertonic saline reserved for severe symptomatic cases and fluid restriction or isotonic saline for most other presentations. 1

Step 1: Assess Symptom Severity and Urgency

Severe symptomatic hyponatremia (seizures, coma, altered consciousness, respiratory distress) requires immediate intervention 2:

• Administer 3% hypertonic saline as 100-150 mL IV bolus over 10 minutes, repeatable up to 3 times at 10-minute intervals 1, 3
• Target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1
• Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 4
• Monitor serum sodium every 2 hours during initial correction 1

Mild to moderate symptoms (nausea, headache, confusion, weakness) or asymptomatic hyponatremia require a more measured approach based on volume status 2, 5.

Step 2: Determine Volume Status and Serum Osmolality

Obtain initial diagnostic workup 1:

• Serum and urine osmolality
• Urine sodium concentration
• Urine electrolytes
• Serum uric acid
• Assessment of extracellular fluid volume status (look for orthostatic hypotension, dry mucous membranes, skin turgor for hypovolemia; peripheral edema, ascites, jugular venous distention for hypervolemia) 1

Confirm hypotonic hyponatremia (serum osmolality <275 mOsm/kg) to exclude pseudohyponatremia from hyperglycemia or hyperlipidemia 5.

Step 3: Treatment Based on Volume Status

Hypovolemic Hyponatremia (Volume Depletion)

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1, 5
• Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 1
• Correct at 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 4
• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For persistent cases, consider urea or vasopressin receptor antagonists (tolvaptan 15 mg once daily) 1, 3
• Avoid fluid restriction in neurosurgical patients at risk for vasospasm 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1, 5
• 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 edema and ascites 1

Step 4: Critical Correction Rate Guidelines

Standard correction rates 1:

• Target 4-8 mmol/L per day
• Absolute maximum: 8 mmol/L in 24 hours for most patients
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): limit to 4-6 mmol/L per day 1, 4

Step 5: Monitoring During Treatment

• Severe symptoms: Check serum sodium every 2 hours initially 1
• Mild symptoms: Check every 4 hours after symptom resolution 1
• Asymptomatic: Check daily initially, then adjust based on response 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5%) and mortality (60-fold increase) 1, 2
• Never use fluid restriction in cerebral salt wasting (common in neurosurgical patients)—this worsens outcomes and requires volume/sodium replacement instead 1, 6
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—overcorrection causes osmotic demyelination syndrome 1, 4
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Never fail to distinguish SIADH from cerebral salt wasting in neurosurgical patients, as treatments are opposite 1, 6

Special Population: Neurosurgical Patients

In patients with CNS pathology, cerebral salt wasting (CSW) is more common than SIADH 1:

• CSW requires volume and sodium replacement (isotonic or hypertonic saline), NOT fluid restriction 1
• Consider fludrocortisone 0.1-0.2 mg daily for severe symptoms 1
• Never restrict fluids in subarachnoid hemorrhage patients at risk of vasospasm 1