What is the initial approach to managing hyponatremia in the emergency department?

Initial Approach to Managing Hyponatremia in the Emergency Department

Immediate Assessment and Symptom-Based Triage

For patients presenting with severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress), immediately administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times, targeting a 4-6 mEq/L increase within 1-2 hours—this is a medical emergency requiring urgent intervention before completing diagnostic workup. 1, 2, 3

For patients with mild or no symptoms (weakness, nausea, headache), proceed with systematic evaluation while initiating conservative management 1, 3.

Essential Initial Diagnostic Workup

Obtain the following immediately upon ED presentation 1:

• Serum osmolality to exclude pseudohyponatremia (hyperglycemia causes 1.6 mEq/L decrease in sodium per 100 mg/dL glucose >100 mg/dL) 1
• Urine sodium concentration (spot sample sufficient; <30 mmol/L suggests hypovolemia with 71-100% positive predictive value) 1
• Urine osmolality (>300 mOsm/kg with urine sodium >20 mEq/L suggests SIADH) 1
• Serum creatinine and BUN to assess renal function and volume status 1
• Volume status assessment through physical examination: check for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia), or jugular venous distention, peripheral edema, ascites (hypervolemia) 1, 4

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

Volume Status Classification and Initial Treatment

Hypovolemic Hyponatremia (Urine Sodium <30 mmol/L)

• Administer isotonic (0.9%) saline for volume repletion 1, 4
• Discontinue diuretics immediately 1
• Avoid hypotonic fluids including lactated Ringer's (130 mEq/L sodium, osmolarity 273 mOsm/L)—this will worsen hyponatremia 5, 1

Euvolemic Hyponatremia (SIADH suspected)

• Implement fluid restriction to 1 L/day as cornerstone therapy 1, 2
• Avoid normal saline—this will worsen SIADH-related hyponatremia 1
• For severe symptoms, use 3% hypertonic saline with target correction of 6 mmol/L over 6 hours 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms present—it worsens fluid overload 1

Critical Correction Rate Guidelines

Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome—this is the single most important safety parameter 1, 6, 2, 3. The FDA label for tolvaptan warns that correction >12 mEq/L/24 hours can cause dysarthria, mutism, dysphagia, lethargy, seizures, coma, and death 6.

For high-risk patients (advanced liver disease, alcoholism, malnutrition, baseline sodium <120 mmol/L), limit correction to 4-6 mmol/L per day 1, 2.

Monitoring Protocol in the ED

• Severe symptoms: Check serum sodium every 2 hours during initial correction 1
• Mild symptoms: Check every 4 hours initially 1
• Once severe symptoms resolve, transition to every 4-6 hour monitoring 1

Special Considerations for Neurosurgical Patients

In patients with subarachnoid hemorrhage, CNS trauma, or recent neurosurgery, distinguish between SIADH and cerebral salt wasting (CSW) 1:

• CSW requires volume and sodium replacement (isotonic or hypertonic saline), NOT fluid restriction 1
• Evidence of true hypovolemia (hypotension, tachycardia, CVP <6 cm H₂O) with high urine sodium >20 mmol/L suggests CSW 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm—this worsens outcomes 1
• Consider fludrocortisone for severe CSW 1

Common ED Pitfalls to Avoid

• Never use fluid restriction as initial treatment for altered mental status—this requires immediate hypertonic saline 1, 3
• Never administer lactated Ringer's for hyponatremia—its hypotonic nature (130 mEq/L sodium) worsens the condition 5, 1
• Never give normal saline to euvolemic patients with SIADH—this paradoxically worsens hyponatremia 1
• Never ignore mild hyponatremia (130-135 mmol/L)—it increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L) 1, 2
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—osmotic demyelination syndrome can occur 2-7 days post-correction 1, 2, 7

Disposition and Admission Criteria

Admit all patients requiring hypertonic saline to an ICU or monitored setting for frequent sodium checks 1, 6. The FDA mandates hospital initiation and re-initiation of tolvaptan with close serum sodium monitoring 6.

Patients with sodium <125 mmol/L, symptomatic hyponatremia, or unclear etiology require admission for continued evaluation and treatment 1, 3.