Management of Hyponatremia: Severity-Based Treatment Algorithm
For mild hyponatremia (serum sodium <130 mmol/L), treat based on volume status and symptoms: hypovolemic patients receive isotonic saline, euvolemic patients require fluid restriction (1 L/day), and hypervolemic patients need fluid restriction (1-1.5 L/day) plus management of underlying disease. 1 For symptomatic or severe hyponatremia (serum sodium ≤120 mmol/L), administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, never exceeding 8 mmol/L in 24 hours. 1, 2
Initial Assessment and Classification
Determine symptom severity first, as this dictates urgency of treatment. Severe symptoms include seizures, coma, altered mental status, or cardiorespiratory distress—these constitute medical emergencies requiring immediate hypertonic saline regardless of sodium level 1, 2. Mild symptoms include nausea, vomiting, headache, weakness, and mild confusion 3, 2.
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, 4. Obtain serum osmolality, urine osmolality, and urine sodium concentration to confirm hypotonic hyponatremia and guide differential diagnosis 1, 4.
Treatment for Severe Symptomatic Hyponatremia (Emergency)
Administer 100 mL boluses of 3% hypertonic saline intravenously over 10 minutes, repeating up to three times at 10-minute intervals until symptoms improve. 1, 5 The goal is to raise serum sodium by 4-6 mmol/L within the first 1-2 hours to reverse cerebral edema 2, 5. Check serum sodium every 2 hours during initial correction 1.
Critical safety limit: Never exceed 8 mmol/L correction in any 24-hour period to prevent osmotic demyelination syndrome. 1, 2 For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy), limit correction to 4-6 mmol/L per day 1, 6. After symptoms resolve, transition to maintenance therapy based on volume status 1.
Treatment for Mild Hyponatremia (Serum Sodium <130 mmol/L)
Hypovolemic Hyponatremia
Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/hour initially, then 4-14 mL/kg/hour based on clinical response 1. Discontinue any diuretics immediately 1. Urine sodium <30 mmol/L predicts good response to saline infusion 1. Continue isotonic fluids until euvolemia is achieved, monitoring serum sodium every 4-6 hours 1.
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day (or <800 mL/day for refractory cases) is the cornerstone of treatment. 1, 2 If fluid restriction fails after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1. For persistent hyponatremia despite these measures, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 7, 2.
Confirm SIADH diagnosis: serum osmolality <275 mOsm/kg, urine osmolality >100 mOsm/kg (typically >300 mOsm/kg), urine sodium >20-40 mEq/L, clinical euvolemia, and normal thyroid/adrenal/renal function 1, 4. Rule out medications causing SIADH (SSRIs, carbamazepine, NSAIDs, opioids, chemotherapy) 1.
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1, 3 Temporarily discontinue diuretics if sodium <125 mmol/L 1. For cirrhotic patients, consider albumin infusion (8 g per liter of ascites removed) alongside fluid restriction 1. Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema 1.
Treat the underlying condition: optimize heart failure therapy with ACE inhibitors, beta-blockers, and aldosterone antagonists before adding specific hyponatremia treatments 1. For refractory cases despite fluid restriction and guideline-directed therapy, consider tolvaptan 15 mg once daily with close monitoring 1, 7.
Special Populations and Considerations
Neurosurgical Patients
Distinguish cerebral salt wasting (CSW) from SIADH—they require opposite treatments 1. CSW presents with true hypovolemia (orthostatic hypotension, CVP <6 cm H₂O), urine sodium >20 mmol/L despite volume depletion, and requires aggressive volume and sodium replacement with isotonic or hypertonic saline 1. Never use fluid restriction in CSW as it worsens outcomes and increases cerebral ischemia risk. 1
For subarachnoid hemorrhage patients at risk of vasospasm, avoid fluid restriction and consider fludrocortisone 0.1-0.2 mg daily to prevent natriuresis 1. Hydrocortisone may also prevent natriuresis in these patients 1.
Cirrhotic Patients
Use more conservative correction rates (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours) due to exceptionally high risk of osmotic demyelination syndrome 1, 6. Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1. Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss, as fluid follows sodium 1.
Elderly Patients (≥80 years)
For thiazide-induced hyponatremia, discontinue the offending diuretic immediately and initiate fluid restriction to 1000-1500 mL/day 6. Use more conservative correction rates (4-6 mmol/L per day) in elderly patients 6. After resolution, maintain blood pressure control with non-thiazide antihypertensives (ARB, calcium channel blocker, beta-blocker) 6.
Monitoring and Safety
Check serum sodium every 2 hours during initial correction of severe symptoms, then every 4-6 hours after symptom resolution 1, 6. Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1, 6.
If overcorrection occurs (>8 mmol/L in 24 hours), immediately discontinue current fluids, switch to D5W (5% dextrose in water), and consider administering desmopressin to slow or reverse the rapid rise 1. The goal is to bring total 24-hour correction back to ≤8 mmol/L from baseline 1.
Common Pitfalls to Avoid
Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome. 1, 2 Do not use fluid restriction as initial treatment for altered mental status from hyponatremia; this is a medical emergency requiring hypertonic saline 1. Avoid hypotonic fluids (0.45% saline, lactated Ringer's, D5W) in any patient with hyponatremia, as they worsen the condition 1.
Do not ignore mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild chronic hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and mortality (60-fold increase with sodium <130 mmol/L) 1, 2. Do not stop diuretics prematurely in heart failure patients with mild hyponatremia (126-135 mmol/L) if volume overload persists, as persistent congestion worsens outcomes 1.