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

Approach to Hyponatremia

The initial approach to hyponatremia requires immediate assessment of symptom severity and volume status, followed by targeted treatment based on these findings—with severe symptomatic hyponatremia requiring emergent 3% hypertonic saline, while asymptomatic cases are managed according to whether the patient is hypovolemic, euvolemic, or hypervolemic. 1

Initial Assessment and Classification

Determine symptom severity first, as this dictates urgency of treatment:

• Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) require immediate intervention regardless of sodium level 1, 2
• Mild symptoms include nausea, vomiting, weakness, headache, confusion 1, 3
• Asymptomatic patients can be managed more conservatively 1

Classify by volume status through physical examination:

• Hypovolemic: dry mucous membranes, decreased skin turgor, orthostatic hypotension, tachycardia 1, 4
• Euvolemic: no edema, normal blood pressure, normal skin turgor 1, 5
• Hypervolemic: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1, 4

Obtain essential laboratory tests:

• Serum osmolality, urine osmolality, urine sodium concentration 1, 2
• Serum creatinine, BUN, glucose, thyroid function 1
• Uric acid (levels <4 mg/dL suggest SIADH with 73-100% positive predictive value) 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms resolve 1, 6

Target correction: increase sodium by 4-6 mmol/L over the first 6 hours or until severe symptoms resolve 1, 2

Critical safety limit: do NOT exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3

Monitor sodium levels every 2 hours during initial correction 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends entirely on volume status:

Hypovolemic Hyponatremia

Discontinue diuretics immediately if contributing to hyponatremia 1

Administer isotonic (0.9%) saline for volume repletion 1, 4

• Urine sodium <30 mmol/L predicts 71-100% response to saline infusion 1
• Once euvolemic, reassess and adjust management 1

Avoid hypotonic fluids, as they will worsen hyponatremia 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is first-line treatment 1, 6

If fluid restriction fails (approximately 50% of SIADH patients do not respond):

• Oral urea is highly effective and safe as second-line therapy 6
• Oral sodium chloride tablets 100 mEq three times daily 1
• Vaptans (tolvaptan 15 mg daily, titrate to 30-60 mg) for resistant cases 1, 7

Alternative agents include demeclocycline, lithium, or loop diuretics (less commonly used due to side effects) 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 8

Treat the underlying condition (optimize heart failure management, manage cirrhosis) 1, 3

For cirrhotic patients specifically:

• Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present 1
• Temporarily discontinue diuretics if sodium <125 mmol/L 1

Vasopressin antagonists may be considered in hospitalized patients with persistent severe hyponatremia despite water restriction and guideline-directed medical therapy 8, 7

Special Populations and Critical Distinctions

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting (CSW)

This distinction is critical as treatments are opposite:

SIADH: euvolemic, treat with fluid restriction 1, 5

CSW: hypovolemic with high urine sodium, treat with volume and sodium replacement 1, 5

• Never use fluid restriction in CSW—it worsens outcomes 1
• Consider fludrocortisone or hydrocortisone for CSW in subarachnoid hemorrhage patients 1

High-Risk Patients for Osmotic Demyelination

Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require even more cautious correction at 4-6 mmol/L per day 1, 2

If overcorrection occurs:

• Immediately discontinue current fluids 1
• Switch to D5W (5% dextrose in water) 1
• Consider desmopressin to slow sodium rise 1

Watch for osmotic demyelination syndrome 2-7 days after rapid correction: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1

Common Pitfalls to Avoid

Ignoring mild hyponatremia (130-134 mmol/L)—even mild hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and is associated with cognitive impairment 1, 2

Using normal saline in SIADH—this can worsen hyponatremia as the patient excretes the sodium but retains the water 1

Fluid restriction in CSW—this is harmful and worsens outcomes 1

Overly rapid correction—exceeding 8 mmol/L in 24 hours risks permanent neurological damage 1, 3

Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—this worsens fluid overload 1

Inadequate monitoring during active correction—sodium levels must be checked frequently (every 2-4 hours initially) 1

Monitoring Strategy

For severe symptoms: check sodium every 2 hours during initial correction 1

After symptom resolution: check every 4 hours, then daily 1

For chronic correction: daily sodium monitoring with adjustments to avoid exceeding 8 mmol/L per 24 hours 1, 6