Management of Hyponatremia
For hyponatremia management, treatment must be guided by symptom severity, volume status, and correction rate limits—with severe symptomatic cases requiring immediate 3% hypertonic saline to increase sodium by 6 mmol/L over 6 hours, while chronic asymptomatic cases are managed with fluid restriction and treatment of the underlying cause, always limiting correction to 8 mmol/L per 24 hours to prevent osmotic demyelination syndrome. 1
Initial Assessment and Classification
Hyponatremia is defined as serum sodium <135 mmol/L and should be further investigated when <131 mmol/L, though even mild hyponatremia (130-135 mmol/L) requires attention as it increases fall risk (21% vs 5% in normonatremic patients) and mortality 1, 2. The initial workup must include serum and urine osmolality, urine sodium, and assessment of extracellular fluid volume status to determine if the patient is hypovolemic, euvolemic, or hypervolemic 1.
Severity classification: mild (130-134 mmol/L), moderate (125-129 mmol/L), and severe (<125 mmol/L) 3. Determine acuity: acute (<48 hours) versus chronic (>48 hours), as acute hyponatremia causes more severe symptoms and tolerates faster correction 1, 4.
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)
Administer 3% hypertonic saline immediately with an initial goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 1. This can be given as 100 mL boluses over 10 minutes, repeated up to three times at 10-minute intervals until symptoms improve 1. Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3. Consider ICU admission for close monitoring with serum sodium checks every 2 hours during initial correction 1.
Mild to Moderate Symptomatic or Asymptomatic Hyponatremia
Treatment depends on volume status and underlying etiology, with slower correction rates (4-6 mmol/L per day for high-risk patients) 1.
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1. A spot urine sodium <30 mmol/L has a positive predictive value of 71-100% for response to saline infusion 1. Once euvolemia is achieved, reassess sodium levels 1. For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1.
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment 1. If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1. For resistant cases, consider urea (effective and safe second-line therapy) or vaptans (tolvaptan 15 mg once daily, titrated to 30-60 mg) 1, 5, 6. Almost half of SIADH patients do not respond to fluid restriction as first-line therapy 6.
Common pitfall: Using fluid restriction in cerebral salt wasting (CSW) worsens outcomes—CSW requires volume and sodium replacement, not restriction 1. In neurosurgical patients, distinguish between SIADH and CSW as treatment approaches differ fundamentally 1.
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 7, 1. Discontinue diuretics temporarily if sodium <125 mmol/L 7. In cirrhotic patients, consider albumin infusion alongside fluid restriction 7, 1. Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen ascites and edema 1.
Important: It is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium 7. Fluid restriction may prevent further decrease in serum sodium but rarely improves it significantly 7.
For heart failure patients with persistent severe hyponatremia despite fluid restriction and guideline-directed medical therapy, vasopressin antagonists may be considered short-term 7, 1.
Correction Rate Guidelines and Prevention of Osmotic Demyelination Syndrome
Maximum correction rate: 8 mmol/L in 24 hours for average-risk patients 1, 3. For high-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia, prior encephalopathy), limit correction to 4-6 mmol/L per day 1. Monitor sodium levels every 2 hours during initial correction for severe symptoms, then every 4 hours after symptom resolution 1.
If overcorrection occurs (>8 mmol/L in 24 hours), immediately discontinue current fluids and switch to D5W (5% dextrose in water), and consider administering desmopressin to slow or reverse the rapid rise 1. Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1.
Pharmacological Interventions
Vaptans (Vasopressin Receptor Antagonists)
Tolvaptan is FDA-approved for euvolemic and hypervolemic hyponatremia 5. Start with 15 mg once daily, titrate to 30-60 mg based on response 1, 5. In clinical trials, tolvaptan caused statistically greater increases in serum sodium compared to placebo (4.0 vs 0.4 mEq/L at Day 4, p<0.0001) 5.
Caution in cirrhosis: Tolvaptan carries a higher risk of gastrointestinal bleeding in cirrhotic patients (10% vs 2% placebo) 1, 5. Avoid fluid restriction during the first 24 hours of vaptan therapy to prevent overly rapid correction 5.
Hypertonic Saline (3%)
Reserved for severe symptomatic hyponatremia or imminent liver transplantation 1. Aim for sodium increase of up to 5 mmol/L in the first hour with a limit of 8-10 mmol/L every 24 hours until sodium reaches 130 mmol/L 7, 1. Hypertonic saline may worsen fluid overload in hypervolemic states 1.
Special Population Considerations
Cirrhotic Patients
Hyponatremia in cirrhosis (defined as <130 mmol/L) is associated with higher prevalence of refractory ascites, hepatic encephalopathy (OR 2.36), spontaneous bacterial peritonitis (OR 3.40), and hepatorenal syndrome (OR 3.45) 7, 1. Those with chronic hyponatremia are often asymptomatic and seldom need treatment 7. Require more cautious correction rates (4-6 mmol/L per day) due to higher risk of osmotic demyelination syndrome 7, 1.
Neurosurgical Patients
In subarachnoid hemorrhage patients at risk of vasospasm, avoid fluid restriction 1. Consider fludrocortisone to prevent vasospasm or hydrocortisone to prevent natriuresis 1. Cerebral salt wasting is more common than SIADH in neurosurgical patients and requires volume and sodium replacement with isotonic or hypertonic saline 1.
Monitoring During Treatment
For severe symptoms: check serum sodium every 2 hours during initial correction 1. For moderate symptoms: check every 4 hours initially, then daily 1. Track daily weight (aim for 0.5 kg/day loss without peripheral edema, 1 kg/day with edema) 7. Monitor for signs of overcorrection and osmotic demyelination syndrome throughout treatment 1.
Common Pitfalls to Avoid
- Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant 1
- Overly rapid correction exceeding 8 mmol/L in 24 hours leading to osmotic demyelination syndrome 1
- Using fluid restriction in cerebral salt wasting 1
- Inadequate monitoring during active correction 1
- Failing to recognize and treat the underlying cause 1
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Administering hypotonic fluids in hypovolemic hyponatremia, which worsens the condition 1