How to manage a patient with orthostatic hypotension and hyponatremia who presents with urinary frequency after increasing water intake?

Management of Orthostatic Hypotension with Hyponatremia

This patient should be fluid restricted to 1.5-2 L/day and started on isotonic saline infusion to correct hyponatremia while addressing the underlying orthostatic hypotension. 1

Assessment of Current Situation

The patient presents with a complex clinical picture:

• Recently diagnosed orthostatic hypotension
• Increased water intake at home (likely as self-management for orthostatic hypotension)
• Urinary frequency
• Hyponatremia (Na 122 mEq/L)

This represents a case of hyponatremia secondary to excessive free water intake in a patient with orthostatic hypotension.

Management Algorithm

Step 1: Address the Hyponatremia

• Fluid restriction to 1.5-2 L/day 1, 2
• Initiate isotonic saline (0.9% NaCl) infusion 1
  • Start at a moderate rate (e.g., 75-100 mL/hr)
  • Goal: Increase serum sodium by no more than 8-10 mEq/L in the first 24 hours 3, 4
  • Monitor serum sodium every 4-6 hours initially

Step 2: Manage Orthostatic Hypotension

• Continue appropriate volume repletion with isotonic saline 5
• Consider midodrine (starting at 2.5-5 mg three times daily) once hyponatremia begins to improve 5
  • Last dose should be taken at least 3-4 hours before bedtime to avoid supine hypertension
  • Contraindicated if patient has severe cardiac disease, acute renal failure, urinary retention, or pheochromocytoma

Step 3: Dietary Modifications

• Moderate sodium restriction (2,300-3,000 mg/day) 2
• Avoid excessive free water intake 1
• Consider salt tablets once hyponatremia is corrected 6

Monitoring Parameters

• Serum sodium levels every 4-6 hours initially, then daily
• Blood pressure measurements (supine and standing)
• Fluid intake and output
• Daily weights to assess volume status
• Symptoms of hyponatremia (confusion, headache, nausea, weakness)
• Urinary frequency and symptoms of orthostatic hypotension

Important Considerations and Pitfalls

Hyponatremia Correction Rate

• Avoid overly rapid correction of sodium (>10 mEq/L in 24 hours) to prevent osmotic demyelination syndrome 3, 4
• If correction occurs too rapidly, consider administering desmopressin (DDAVP) and free water to slow the correction 7

Balance Between Competing Needs

• Orthostatic hypotension typically requires increased fluid intake
• Hyponatremia requires fluid restriction
• The key is to provide sodium without excessive free water 1

Common Pitfalls

• Excessive fluid restriction can worsen orthostatic symptoms
• Unrestricted water intake will worsen hyponatremia
• Failure to monitor sodium correction rate can lead to osmotic demyelination syndrome
• Not addressing the underlying cause of orthostatic hypotension

Long-term Management

• Once sodium normalizes (>135 mEq/L), adjust fluid intake to maintain both normal sodium levels and adequate orthostatic blood pressure
• Consider pharmacologic therapy for orthostatic hypotension (midodrine, fludrocortisone) 5
• Educate patient on appropriate fluid and salt intake
• Regular monitoring of electrolytes, especially during hot weather or illness

This balanced approach addresses both the acute hyponatremia and the underlying orthostatic hypotension while avoiding complications from overly aggressive treatment of either condition.