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

Comprehensive Approach to Hyponatremia

Initial Assessment and Classification

Begin by confirming true hypotonic hyponatremia with serum osmolality <280 mOsm/kg, then immediately assess symptom severity to determine urgency of treatment. 1

Essential Initial Workup

• Obtain serum and urine osmolality, urine sodium, urine potassium, serum uric acid, and assess extracellular fluid (ECF) volume status 1
• Check serum creatinine, blood urea nitrogen, glucose, thyroid-stimulating hormone (TSH), and cortisol to rule out endocrine causes 1
• Measure vital signs including orthostatic blood pressure and pulse changes 2
• Assess for clinical signs of volume status: jugular venous distention, mucous membrane moisture, skin turgor, peripheral edema, ascites 1, 3

Volume Status Classification

Hypovolemic hyponatremia indicators:

• Urine sodium <30 mmol/L (71-100% positive predictive value for saline responsiveness) 1
• Clinical signs: orthostatic hypotension, tachycardia, dry mucous membranes, decreased skin turgor 2
• Elevated BUN/creatinine ratio 1

Euvolemic hyponatremia indicators:

• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH 1
• Serum uric acid <4 mg/dL (73-100% positive predictive value for SIADH) 1
• No edema, normal blood pressure, normal skin turgor 1

Hypervolemic hyponatremia indicators:

• Presence of edema, ascites, jugular venous distention 1
• Associated with heart failure, cirrhosis, or nephrotic syndrome 1
• Urine sodium typically <30 mmol/L unless on diuretics 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, confusion, obtundation, or cardiorespiratory distress, immediately administer 3% hypertonic saline with a goal to increase sodium by 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 3

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals 1
• Alternative dosing: calculate initial infusion rate (mL/kg/hour) = body weight (kg) × desired rate of sodium increase (mmol/L/hour) 4
• Critical safety limit: Do not exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3
• Monitor serum sodium every 2 hours during initial correction 1
• Consider ICU admission for close monitoring 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status and underlying etiology:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

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

• Continue isotonic saline until euvolemia is achieved 1
• Once euvolemic, reassess sodium levels and adjust therapy accordingly 1
• Monitor for improvement: if sodium normalizes with volume repletion, the diagnosis is confirmed 1
• Avoid hypotonic fluids as they will worsen hyponatremia 2

Euvolemic Hyponatremia (SIADH)

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

• For mild/asymptomatic cases: restrict fluids to <1 L/day 1
• If no response to fluid restriction after 48-72 hours: add oral sodium chloride 100 mEq (approximately 6 g) three times daily 1
• Monitor sodium levels every 4 hours initially, then daily 1

Pharmacological options for resistant cases:

• Vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg as needed) 1, 5
• Urea 15-30 g/day in divided doses (effective alternative with fewer side effects than vaptans) 1, 3
• Demeclocycline or lithium (less commonly used due to side effects) 1

Important distinction in neurosurgical patients:

• Cerebral salt wasting (CSW) mimics SIADH but requires opposite treatment 1
• CSW indicators: evidence of volume depletion, high urine sodium (>20 mmol/L), occurs after subarachnoid hemorrhage or neurosurgery 1
• CSW treatment: volume and sodium replacement with normal or hypertonic saline, NOT fluid restriction 1
• Consider fludrocortisone 0.1-0.2 mg daily for CSW in subarachnoid hemorrhage patients 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

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

• Discontinue or reduce diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients: consider albumin infusion (6-8 g per liter of ascites drained if performing paracentesis) 1
• Sodium restriction (2-2.5 g/day or 88-110 mmol/day) is more effective than fluid restriction for weight loss in cirrhosis 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1

For resistant hypervolemic hyponatremia:

• Consider tolvaptan 15 mg once daily, titrate cautiously 1, 5
• Caution in cirrhosis: tolvaptan increases gastrointestinal bleeding risk (10% vs 2% placebo) 1, 5
• Monitor closely to prevent overly rapid correction (>8 mmol/L/24 hours) 5

Correction Rate Guidelines

Standard Patients

• Maximum correction: 8 mmol/L in 24 hours 1, 3
• Target rate: 4-6 mmol/L per day for chronic hyponatremia 1
• For acute hyponatremia (<48 hours): faster correction up to 1-2 mmol/L/hour initially is safer 1

High-Risk Patients (Increased Risk of Osmotic Demyelination)

Patients with advanced liver disease, alcoholism, malnutrition, severe hyponatremia (<120 mmol/L), hypokalemia, or prior encephalopathy require more cautious correction at 4-6 mmol/L per day. 1

• Risk of osmotic demyelination syndrome in liver transplant recipients: 0.5-1.5% 1
• Symptoms of osmotic demyelination appear 2-7 days after rapid correction: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 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

• Administer desmopressin 2-4 mcg IV/SC to slow or reverse rapid sodium rise 1
• Goal: bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Monitor sodium levels every 2 hours until stabilized 1

Severity-Based Treatment Thresholds

Sodium 126-135 mmol/L (Mild)

• Continue diuretics with close electrolyte monitoring if on diuretics 1
• No water restriction needed at this level 1
• Address underlying cause 1
• Do not ignore: even mild hyponatremia increases fall risk (21% vs 5%) and mortality (60-fold increase if <130 mmol/L) 1, 3

Sodium 121-125 mmol/L (Moderate)

• For hypervolemic: fluid restriction to 1-1.5 L/day 1
• For euvolemic: fluid restriction to 1 L/day 1
• Consider discontinuing diuretics temporarily 1
• Monitor sodium daily 1

Sodium ≤120 mmol/L (Severe)

• Stop diuretics immediately 1
• For asymptomatic: severe fluid restriction plus albumin infusion (if cirrhotic) 1
• For symptomatic: 3% hypertonic saline as described above 1
• Maximum correction: 4-6 mmol/L per day in high-risk patients, 8 mmol/L per day in standard patients 1

Special Population Considerations

Cirrhotic Patients

• Hyponatremia in cirrhosis reflects worsening hemodynamic status 1
• Sodium ≤130 mmol/L increases risk of: spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), hepatic encephalopathy (OR 2.36) 1
• Hyponatremia is primarily dilutional and hypervolemic 1
• Correction rate: 4-6 mmol/L per day maximum 1
• Albumin infusion improves sodium levels and outcomes 1

Neurosurgical Patients

• Even mild hyponatremia requires closer monitoring as it may indicate CSW or SIADH 1
• In subarachnoid hemorrhage patients at risk for vasospasm: do NOT use fluid restriction 1
• Maintain adequate volume status to prevent cerebral ischemia 1
• Consider fludrocortisone or hydrocortisone to prevent natriuresis 1

Heart Failure Patients

• Fluid restriction benefit for congestive symptoms is uncertain 1
• Limit fluid intake to approximately 2 L/day for most hospitalized patients 1
• For persistent severe hyponatremia despite guideline-directed medical therapy: consider short-term vasopressin antagonists 1
• Monitor for worsening volume overload if using hypertonic saline 1

Common Pitfalls to Avoid

• Overly rapid correction (>8 mmol/L in 24 hours) causing osmotic demyelination syndrome 1
• Using fluid restriction in cerebral salt wasting (worsens outcomes) 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
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant 1, 3
• Administering normal saline to euvolemic patients with SIADH (worsens hyponatremia) 1

Monitoring Requirements

During Active Correction

• Severe symptoms: check sodium every 2 hours 1
• After symptom resolution: check sodium every 4 hours 1
• Once stable: check sodium daily 1
• Monitor for signs of osmotic demyelination syndrome for 7 days after correction 1

Long-term Management

• Regular sodium monitoring based on underlying condition 1
• Assess volume status at each visit 1
• Review medication list for contributing agents 1
• Monitor for neurocognitive symptoms, falls, and fractures 3