What is the initial approach to treating hyponatremia (low sodium levels)?

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia requires immediate assessment of symptom severity and volume status, with severely symptomatic patients (seizures, coma, altered mental status) requiring urgent 3% hypertonic saline to increase sodium by 6 mmol/L over 6 hours, while asymptomatic or mildly symptomatic patients should be managed based on their volume status—hypovolemic patients receive isotonic saline, euvolemic patients (SIADH) receive fluid restriction to 1 L/day, and hypervolemic patients receive fluid restriction to 1-1.5 L/day. 1

Immediate Assessment of Symptom Severity

The first critical step is determining whether the patient has severe symptoms requiring emergency intervention:

• Severe symptoms include seizures, coma, somnolence, obtundation, altered mental status, confusion, or cardiorespiratory distress—these constitute a medical emergency 1, 2, 3
• Mild symptoms include nausea, vomiting, headache, weakness, or nonspecific complaints 1, 2
• Asymptomatic patients may still require treatment if sodium is significantly low 1

Emergency Management for Severe Symptomatic Hyponatremia

For patients with severe neurological symptoms, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1, 2, 3

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve 1
• The goal is to increase sodium by 4-6 mmol/L within 1-2 hours to reverse hyponatremic encephalopathy 2
• Critical safety limit: Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3
• Monitor serum sodium every 2 hours during initial correction 1
• ICU admission is recommended for close monitoring 1

Initial Diagnostic Workup

While initiating treatment for severe symptoms, obtain the following to determine underlying cause:

• Serum osmolality to confirm hypotonic hyponatremia 1, 3
• Urine osmolality and urine sodium concentration to differentiate causes 1, 3
• Assessment of extracellular fluid volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia) versus peripheral edema, ascites, jugular venous distention (hypervolemia) 1, 3
• Serum creatinine, blood urea nitrogen, thyroid function, and cortisol if indicated 1

A urine sodium <30 mmol/L suggests hypovolemic hyponatremia with 71-100% positive predictive value for response to saline 1, while urine sodium >20 mmol/L with high urine osmolality (>500 mOsm/kg) suggests SIADH 1

Treatment Based on Volume Status (For Non-Severe Cases)

Hypovolemic Hyponatremia

• Discontinue diuretics immediately 1
• Administer isotonic (0.9%) saline for volume repletion 1, 3
• This is appropriate when there is true volume depletion with urine sodium <30 mmol/L 1
• Once euvolemic, reassess and adjust management 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3
• Avoid fluid restriction during the first 24 hours if using hypertonic saline to prevent overly rapid correction 4
• 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) 1, 4

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 3
• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1

Critical Correction Rate Guidelines

The maximum correction rate is 8 mmol/L in 24 hours for all patients to prevent osmotic demyelination syndrome. 1, 2, 3

• For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy, severe hyponatremia <120 mmol/L), use even more cautious correction of 4-6 mmol/L per day 1, 2
• Chronic hyponatremia (>48 hours duration) requires slower correction than acute hyponatremia (<48 hours) 1, 5
• If overcorrection occurs, immediately discontinue current fluids, switch to D5W, and consider desmopressin to relower sodium 1

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW) as treatment approaches differ fundamentally 1, 6:

• CSW requires volume and sodium replacement (isotonic or hypertonic saline), NOT fluid restriction 1, 6
• CSW is characterized by true hypovolemia with evidence of volume depletion (hypotension, tachycardia, dry mucous membranes) despite high urine sodium 1
• Consider fludrocortisone for CSW, especially in subarachnoid hemorrhage patients 1, 6
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Common Pitfalls to Avoid

• Overly rapid correction (>8 mmol/L in 24 hours) leading to osmotic demyelination syndrome 1, 2, 5
• Using fluid restriction in CSW, which worsens outcomes 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Inadequate monitoring during active correction 1, 7
• Failing to recognize and treat the underlying cause 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild hyponatremia increases fall risk (21% vs 5%) and mortality 1, 2