17- HYPONATREMIA

• Hyponatremia


  Serum Na < 135
• Severity of hyponatremia


  • Mild: 130-134
  • Moderate: 122-129
  • Severe: <122
• Acute hyponatremia


  Onset of hyponatremia < 48 hours by lab results, must have a previous normal Na result within the past 48 hours
• Chronic hyponatremia


  Onset of hyponatremia > 48 hours
• Approach to hyponatremia


  1. Determine serum osmolality

  2. Determine volume status
• True hyponatremia


  Low serum osmolality
• Pseudohyponatremia


  Normal/high serum osmolality due to hyperlipidemia, hyperproteinemia, hyperglycemia or mannitol
• Hypovolemic hyponatremia


  • Dehydration, more sodium loss than water loss
  • Measure urine sodium to determine cause
• Causes of low urinary Na (<10, FeNa <1%)

  • GI (diarrhea, vomiting)
  • Sweating, burns
  • Third spacing (pancreatitis)
  • Diuretics
• Causes of high urinary Na (>20, FeNa >1%)


  • ATN
  • Hypoaldosteronism (Addison's)
• Treatment for hypovolemic hyponatremia


  IV NS 0.9% until dehydration parameters normalize
• Hypervolemic hyponatremia


  • May be due to CHF, liver disease/hypoalbuminemia/cirrhosis, nephrotic syndrome, acute or chronic renal failure
  • Treatment: salt and water restriction, diuresis, treat underlying condition
• Euvolemic hyponatremia


  • Check urine osmolality
  • If <100 - psychogenic polydipsia
  • If >100 - renal tubular acidosis type IV, Addison's disease, hypothyroidism, SIADH
• SIADH


  • Syndrome of inappropriate ADH secretion
  • Features: hyponatremia, low serum osmolality, high urine Na, high urine osmolality, euvolemic
  • Overdrive of aquaporins results in excessively concentrating urine even when blood is dilute
• Triggers for inappropriate ADH secretion in SIADH

  • Lung: cancer, pneumonia, asthma, CF, sarcoidosis
  • Brain: infection, hemorrhage SAH, MS, GBS, trauma
  • Pain
  • Malignancy: small cell lung cancer, GI, GU
  • Drugs: SSRIs, TCAs, sulfonylureas, vincristine, cyclophosphamide
• Treatment for SIADH


  • Fluid resuscitation (<800 ml/day)
  • IV hypertonic saline + loop diuretic
  • Severe symptoms: ADH antagonists IV tolvaptan or conivaptan
  • Chronic SIADH: Demeclocycline (blocks ADH action at collecting duct)
• Acute hyponatremia


  Onset < 48 hours, usually symptomatic (brain edema, water shifts from extra to intracellular spaces)

  • Usually symptomatic (brain edema, water shifts from extra to intracellular spaces)

  in contrast to chronic hyponatremia which is usually asymptomatic

  • Presents as nausea & vomiting, anorexia, headache, lethargy, agitation, decreased

  reflexes, muscle cramps and weakness
• Treatment for acute hyponatremia

  • 3% hypertonic saline
  • Correction should not exceed 8 mmol in first 8 hrs, rapid correction >10-12 mmol/L may lead to osmotic demyelination syndrome