Treatment of Chronic Hyponatremia
For chronic hyponatremia, the cornerstone of treatment depends on volume status: fluid restriction to 1 L/day for euvolemic hyponatremia (SIADH), isotonic saline for hypovolemic hyponatremia, and fluid restriction (1-1.5 L/day) plus albumin for hypervolemic hyponatremia (cirrhosis, heart failure), with the critical safety rule being never to exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1
Initial Assessment and Classification
Determine the chronicity first: chronic hyponatremia is defined as lasting >48 hours, which allows brain adaptation through extrusion of electrolytes and organic osmolytes 2. This distinction is critical because chronic hyponatremia requires slower correction rates than acute hyponatremia 1, 2.
Assess volume status through physical examination:
- Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia 1
- Euvolemic signs: no edema, normal blood pressure, moist mucous membranes 1
- Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1
Obtain essential laboratory tests: serum and urine osmolality, urine sodium, urine electrolytes, serum uric acid 1. A urine sodium <30 mmol/L suggests hypovolemic hyponatremia with 71-100% positive predictive value for response to saline 1. Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1.
Treatment Based on Volume Status
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH 1, 3. If no response to fluid restriction after several days, add oral sodium chloride 100 mEq three times daily 1.
For moderate hyponatremia (120-125 mmol/L) that is asymptomatic or mildly symptomatic, implement fluid restriction to 1000 mL/day 1. For resistant cases, consider pharmacological options:
Tolvaptan (vasopressin receptor antagonist): Start at 15 mg once daily, can titrate to 30 mg then 60 mg as needed 1, 4. In clinical trials, tolvaptan increased serum sodium by 4.0 mEq/L at Day 4 versus 0.4 mEq/L with placebo (p<0.0001), and by 6.2 mEq/L at Day 30 versus 1.8 mEq/L with placebo 4. However, use with extreme caution due to risk of overly rapid correction 1, 3.
Urea: Effective alternative to vaptans, though associated with poor palatability and gastric intolerance 3. Experimental data suggest lower incidence of myelinolysis compared to hypertonic saline 2.
Other options: Demeclocycline, lithium, or loop diuretics may be considered for resistant SIADH 1.
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1. Normal saline contains 154 mEq/L sodium and is truly isotonic 1. Continue isotonic fluids until euvolemia is achieved 1.
For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring, but this is rare in hypovolemic states 1.
Hypervolemic Hyponatremia (Cirrhosis, Heart Failure)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1. Temporarily discontinue diuretics if sodium <125 mmol/L 1.
For cirrhotic patients, consider albumin infusion alongside fluid restriction 1. Albumin has been shown to improve serum sodium levels in hospitalized cirrhotic patients 1.
Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1. It is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium in cirrhotic patients 1.
For persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy, vasopressin antagonists may be considered short-term 1. However, tolvaptan carries a higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 1.
Critical Correction Rate Guidelines
The maximum correction rate must never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3, 2. For asymptomatic or mildly symptomatic chronic hyponatremia, aim for 4-6 mmol/L per day 1.
High-Risk Populations Requiring Slower Correction (4-6 mmol/L per day):
- Advanced liver disease 1, 2
- Alcoholism 1, 2
- Malnutrition 1, 2
- Prior encephalopathy 1
- Hypokalemia 2
- Burns 2
The rate of correction should be no more than 0.5 mmol/L per hour in these high-risk patients 5, 2.
Monitoring Protocol
For chronic hyponatremia being actively corrected:
- Check serum sodium every 4 hours initially until stable 1
- After resolution of symptoms, monitor daily 1
- Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours:
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
- Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 1, 2
- The goal is to bring total 24-hour correction to no more than 8 mmol/L from the starting point 1
Recent experimental data suggest that rapidly decreasing serum sodium through hypotonic fluids and dDAVP in overly corrected patients could greatly reduce the risk of myelinolysis 2.
Special Considerations
Even mild chronic hyponatremia (130-135 mmol/L) should not be ignored, as it is associated with increased fall risk (21% vs 5% in normonatremic patients), cognitive impairment, gait disturbances, and increased mortality 1, 3. In prospective studies, hyponatremic patients had higher rates of new fractures over 7.4 years (23.3% vs 17.3%, p<0.004) 3.
In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches differ fundamentally 1. CSW requires volume and sodium replacement, not fluid restriction, and using fluid restriction in CSW worsens outcomes 1.
For cirrhotic patients with hyponatremia, serum sodium ≤130 mEq/L increases risk for hepatic encephalopathy (OR 2.36), hepatorenal syndrome (OR 3.45), and spontaneous bacterial peritonitis (OR 3.40) 1.
Common Pitfalls to Avoid
- Overly rapid correction exceeding 8 mmol/L in 24 hours leading to osmotic demyelination syndrome 1, 3
- Inadequate monitoring during active correction 1
- Using fluid restriction in cerebral salt wasting 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 1