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

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia must be guided by three critical factors: symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and the rate of correction needed to prevent osmotic demyelination syndrome. 1

Immediate Assessment

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

• Severe symptoms (seizures, coma, somnolence, obtundation, cardiorespiratory distress) require immediate intervention 1, 2
• Mild symptoms (nausea, vomiting, headache, weakness) allow for more measured correction 1
• Asymptomatic hyponatremia permits slower, safer correction strategies 1

Assess volume status through physical examination looking for:

• Hypovolemia: hypotension, tachycardia, dry mucous membranes, decreased skin turgor 1
• Euvolemia: no edema, normal blood pressure, normal skin turgor 1
• Hypervolemia: jugular venous distention, peripheral edema, ascites, orthopnea 1

Obtain initial laboratory workup including serum and urine osmolality, urine sodium, urine electrolytes, serum uric acid, and assessment of renal, thyroid, and adrenal function 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately as 100-150 mL IV bolus over 10 minutes 1, 3, 4:

• Goal: Increase serum sodium by 4-6 mmol/L over the first 1-2 hours or until severe symptoms resolve 1, 2
• Can repeat bolus up to three times at 10-minute intervals if symptoms persist 3
• Maximum correction: Do not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Monitor sodium levels every 2 hours during initial correction 1

The 250 mL bolus is more effective than 100 mL (52% vs 32% achieving ≥5 mmol/L rise within 4 hours) without increasing overcorrection risk 3.

Mild Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia

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

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

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2:

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider urea or vasopressin receptor antagonists (tolvaptan 15 mg daily, titrated to 30-60 mg) 1, 5, 2
• Tolvaptan increases serum sodium significantly more than placebo, with effects seen as early as 8 hours 5

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1:

• Consider albumin infusion in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1

Critical Correction Rate Guidelines

Never exceed 8 mmol/L correction in 24 hours for most patients 1, 2, 6:

• High-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia) require even slower correction at 4-6 mmol/L per day 1
• For severe symptoms: Correct 6 mmol/L over first 6 hours, then slow correction rate 1
• Overly rapid correction causes osmotic demyelination syndrome, occurring 2-7 days post-correction with dysarthria, dysphagia, oculomotor dysfunction, and quadriparesis 1

Special Considerations and Common Pitfalls

Distinguish SIADH from cerebral salt wasting (CSW) in neurosurgical patients 1:

• SIADH: Treat with fluid restriction
• CSW: Treat with volume and sodium replacement; fluid restriction worsens outcomes 1

Monitor for overcorrection: If sodium rises >8 mmol/L in 24 hours, immediately switch to D5W and consider desmopressin to relower sodium 1.

Avoid fluid restriction in subarachnoid hemorrhage patients at risk for vasospasm 1.

Check urine sodium and osmolality to guide diagnosis:

• Urine sodium >20 mmol/L with high urine osmolality (>300 mOsm/kg) suggests SIADH 1
• Urine sodium <30 mmol/L suggests hypovolemia 1

Even mild hyponatremia (130-135 mmol/L) increases fall risk (21% vs 5% in normonatremic patients) and mortality, and should not be ignored 1, 2.