Urine Studies

Impact of Diuretics

• Administration of loop or thiazide diuretics will alter interpretation of UNa
• Expect UNa to be high after diuretic dosing
• Fractional excretion of urea can be helpful to interpret sodium handling in the presence of diuretics
  • Urea re-absorbed proximal to site of action of diuretics
  • Low FeUrea (<55%) suggests appropriate sodium retention
  • High FeUrea (>55%) suggests inappropriate sodium retention

Management

Severe Symptoms

• Seizures, coma, altered mental status possible when sodium very low (< 120 mEq/L)

Give 3% hypertonic saline regardless of etiology

Can bolus 100-250 mL over 15 minutes or start infusion at 25-50 mL/hr

Hypovolemic Hyponatremia

• Isotonic saline functions both as solute replacement and volume replacement
• Normal saline contains 154 mEq/L of sodium, equating to osmolality of 308 mOsm/L
  • Administration will replace sodium and volume losses
• Eventually, volume will be restored and volume-related ADH release will be turned off
  • Important to correct at a safe level, 6-8 mEq/L/day

Volume resuscitated after 2 liters                                                       Volume resuscitated after 5 liters

Hypervolemic Hyponatremia

• Volume restriction
• Symptoms very rare, so aggressive volume restrictions often not needed
  • Progression to significant hyponatremia often a very chronic process
• Combination of loop diuresis and ACE inhibitor effective at improving sodium

Other Less Common Causes of Hyponatremia

• Adrenal insufficiency
  • Suspect in hypotensive, hypokalemic, hyponatremic patients
  • Hydrocortisone supplementation
• Hypothyroidism
  • Rare, responds well to LT4
• Hypokalemia
  • Reduction in total body potassium will lead to osmotic shift of sodium
  • Potassium repletion always indicated when treating hyponatremia