What are the management steps for hyponatremia (low sodium levels)?

Hyponatremia: Presentation and Management

Clinical Presentation

Hyponatremia (serum sodium <135 mEq/L) presents with symptoms ranging from mild to life-threatening, depending on severity, rapidity of onset, and duration 1, 2.

Mild symptoms (sodium 130-134 mEq/L) include nausea, vomiting, weakness, headache, and mild neurocognitive deficits 3. Even mild chronic hyponatremia increases fall risk (23.8% vs 16.4% in normonatremic patients), fracture rates, cognitive impairment, gait disturbances, and mortality 2, 1.

Severe symptoms (sodium <125 mEq/L) include delirium, confusion, impaired consciousness, ataxia, seizures, and rarely brain herniation and death 3, 4. Severely symptomatic hyponatremia with seizures, coma, or cardiorespiratory distress is a medical emergency requiring immediate hypertonic saline 2, 1.

Initial Diagnostic Workup

Begin evaluation when serum sodium drops below 131 mmol/L, though even mild hyponatremia (130-135 mmol/L) warrants attention 1. The workup should include:

• Serum and urine osmolality to exclude pseudohyponatremia 1, 4
• Urine sodium concentration (spot urine sodium <30 mmol/L predicts 71-100% response to saline; >20-40 mmol/L with high urine osmolality suggests SIADH) 1, 4
• Uric acid (serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH) 1
• Extracellular fluid volume status assessment through physical examination: look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia) or peripheral edema, ascites, jugular venous distention (hypervolemia) 1, 4
• Serum glucose (adjust sodium by 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL to exclude pseudohyponatremia) 1
• Thyroid-stimulating hormone and cortisol to rule out endocrine causes 1

Do not obtain ADH or natriuretic peptide levels—these are not supported by evidence and delay treatment 1.

Management Algorithm Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

Immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1, 2. Give 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals 1. This is a medical emergency—do not delay for fluid restriction 1.

• Monitor serum sodium every 2 hours during initial correction 1
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Calculate sodium deficit: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment is based on volume status:

Management Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1. Initial infusion rate of 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1. Urine sodium <30 mmol/L predicts good response to saline 1.

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2. If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1.

For persistent cases despite fluid restriction, consider:

• Urea (effective but poor palatability) 2, 1
• Vasopressin receptor antagonists (tolvaptan): Start 15 mg once daily, titrate to 30-60 mg based on response 1, 5. Tolvaptan increases serum sodium significantly more than placebo, with effects seen within 8 hours 5.

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1. Temporarily discontinue diuretics until sodium improves 1.

• For cirrhotic patients: Consider albumin infusion alongside fluid restriction 1. Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema 1.
• Sodium restriction (not fluid restriction) results in weight loss in cirrhosis, as fluid follows sodium 1

Critical Correction Rate Guidelines

The maximum correction rate is 8 mmol/L in 24 hours for all patients 1, 2. Exceeding this risks osmotic demyelination syndrome, which causes dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, and can be fatal 1.

High-risk patients require even slower correction (4-6 mmol/L per day) 1:

• Advanced liver disease
• Alcoholism
• Malnutrition
• Prior encephalopathy
• Severe hyponatremia (<120 mmol/L)

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 1. Target relowering to bring total 24-hour correction to no more than 8 mmol/L from baseline 1.

Special Populations

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW)—treatment approaches are opposite 1. CSW is more common in neurosurgical patients and requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1. For severe CSW symptoms, use 3% hypertonic saline plus fludrocortisone in ICU 1.

Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1. Consider fludrocortisone or hydrocortisone to prevent natriuresis 1.

Cirrhotic Patients

Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1. Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 5 and is associated with increased mortality with long-term use 1.

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L)—it increases mortality and fall risk 1
• Never use fluid restriction as initial treatment for severe symptomatic hyponatremia—this is a medical emergency requiring hypertonic saline 1
• Never exceed 8 mmol/L correction in 24 hours—overcorrection causes osmotic demyelination syndrome 1, 2
• Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens edema and ascites 1
• Inadequate monitoring during active correction leads to complications 1
• Failing to identify and treat the underlying cause results in recurrence 1