Management of Hyponatremia

Initial Assessment and Classification

Hyponatremia management is determined by three critical factors: volume status (hypovolemic, euvolemic, or hypervolemic), symptom severity (asymptomatic, mild, or severe), and acuity (acute <48 hours vs. chronic >48 hours). 1

Diagnostic Workup

Obtain serum and urine osmolality, urine sodium, urine electrolytes, serum uric acid, and assess extracellular fluid volume status to determine the underlying cause 1
Check serum creatinine, thyroid-stimulating hormone (TSH), and cortisol to exclude hypothyroidism and adrenal insufficiency 1
Physical examination for volume status includes checking for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemia), or peripheral edema, ascites, jugular venous distention (hypervolemia) 1
Urine sodium <30 mmol/L suggests hypovolemic hyponatremia with 71-100% positive predictive value for saline responsiveness 1
Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

Management Based on Symptom Severity

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

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1

Give 100 mL boluses of 3% saline over 10 minutes, repeating up to three times at 10-minute intervals until symptoms improve 2
Monitor serum sodium every 2 hours during initial correction 1
Maximum correction must not exceed 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome 1
After initial 6 mmol/L correction, limit additional correction to only 2 mmol/L in the following 18 hours 2
Discontinue 3% saline once severe symptoms resolve and transition to protocols for mild symptoms or asymptomatic hyponatremia 2

Mild to Moderate Symptomatic Hyponatremia (Nausea, Headache, Confusion)

Symptoms include nausea, vomiting, muscle cramps, gait instability, lethargy, weakness, headaches, and dizziness 3
Treatment approach depends on volume status (see below) 1
Monitor serum sodium every 4-6 hours initially 1

Asymptomatic Hyponatremia

Even mild chronic hyponatremia (130-135 mmol/L) is not benign and increases hospital mortality 60-fold (11.2% vs 0.19%) 3
Treatment based on volume status and underlying cause 1
Correction rate should be slower: 4-6 mmol/L per day for chronic cases 1

Management Based on Volume Status

Hypovolemic Hyponatremia (Dehydration, Diuretic Use)

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1

Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
Urine sodium <30 mmol/L predicts good response to saline infusion 1
For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1
Maximum correction: 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1

If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
For severe symptomatic cases, use 3% hypertonic saline with careful monitoring 1
Alternative pharmacological options include vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg), urea, demeclocycline, or lithium 1
Serum uric acid <4 mg/dL supports SIADH diagnosis 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1000-1500 mL/day for serum sodium <125 mmol/L. 1

Discontinue diuretics temporarily 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 are present, as it may worsen edema and ascites 1
Sodium restriction (2-2.5 g/day or 88-110 mmol/day) is more effective than fluid restriction alone for weight loss in cirrhosis 1
Vasopressin receptor antagonists (tolvaptan) may be considered for clinically significant hyponatremia resistant to fluid restriction, starting at 15 mg once daily 1

Critical Correction Rate Guidelines

The single most important safety principle: never exceed 8 mmol/L correction in 24 hours. 1

Standard-Risk Patients

Target correction: 4-8 mmol/L per day 1
Maximum: 10-12 mmol/L in 24 hours 1

High-Risk Patients (Advanced Liver Disease, Alcoholism, Malnutrition, Prior Encephalopathy)

More cautious correction: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
These patients have 0.5-1.5% risk of osmotic demyelination syndrome even with careful correction 1

Acute vs. Chronic Hyponatremia

Acute hyponatremia (<48 hours): can tolerate faster correction with less risk of osmotic demyelination 1
Chronic hyponatremia (>48 hours): requires slower correction; avoid exceeding 1 mmol/L/hour 1

Special Considerations: Neurosurgical Patients (SIADH vs. Cerebral Salt Wasting)

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

SIADH (Euvolemic)

Characterized by normal to slightly elevated central venous pressure, euvolemic state 1
Treatment: fluid restriction to 1 L/day 1

Cerebral Salt Wasting (Hypovolemic)

Characterized by low central venous pressure (<6 cm H₂O), clinical signs of hypovolemia (orthostatic hypotension, tachycardia, dry mucous membranes) 1
Treatment focuses on volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
For severe symptoms: 3% hypertonic saline plus fludrocortisone (0.1-0.2 mg daily) in ICU setting 1
Hydrocortisone may be used 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 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately intervene to prevent osmotic demyelination syndrome. 1

Discontinue current fluids and switch to D5W (5% dextrose in water) to relower sodium levels 1
Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 1
Target: bring total 24-hour correction back to ≤8 mmol/L from baseline 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

Overly rapid correction of chronic hyponatremia (>8 mmol/L in 24 hours) leading to osmotic demyelination syndrome 1
Inadequate monitoring during active correction 1
Using fluid restriction in cerebral salt wasting, which worsens outcomes 1
Failing to recognize and treat the underlying cause 1
Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant, when it increases fall risk and mortality 3
Misdiagnosing volume status in neurosurgical patients, leading to inappropriate treatment 1

What is the recommended management approach for hyponatremia based on volume status, acuity, and symptom severity?

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