Hyponatremia

Hyponatremia

David Ray Velez, MD

Definition: Sodium (Na) < 135 mEq/L

  • Acute Hyponatremia: < 48 Hours
  • Chronic Hyponatremia: > 48 Hours or Unknown

The Most Common Electrolyte Disorder Overall

Severity

  • Mild: Na < 135 mEq/L
  • Moderate: Na < 130 mEq/L
  • Severe: Na < 120 mEq/L
  • *Definitions Vary and Multiple Different Levels Have Been Used in Classification

Classification

  • Hypovolemic Hyponatremia: Total Body Water Decreases Less Than a Decrease in Total Body Sodium
  • Euvolemic Hyponatremia: Total Body Water Increases with a Stable Total Body Sodium
  • Hypervolemic Hyponatremia: Total Body Water Increases More Than an Increase in Total Body Sodium

Causes

  • Hypovolemic Hyponatremia
    • Vomiting
    • Diarrhea
    • Third-Space Fluid Losses
    • Diuretics
    • Cerebral Salt-Wasting Syndrome
    • Mineralocorticoid Deficiency
  • Euvolemic Hyponatremia
    • Fluid Overload/Dilutional
    • Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)
    • Vasopressin
    • Ecstasy (MDMA) – Increased Thirst and ADH Secretion
    • Oxytocin – Used for Labor Induction but Can Stimulate Vasopressin Receptors (Similar to ADH)
  • Hypervolemic Hyponatremia
    • Congestive Heart Failure (CHF)
    • Renal Failure
    • TURP-Syndrome: Excessive Irrigating Fluid Used During TURP is Absorbed Through Prostatic Veins Causing Severe Hyponatremia
      • Less Common with Newer Irrigating Fluids
      • Risk for Respiratory Distress and Neurologic Complications (Headache, Seizure, Coma)

Pseudohyponatremia

  • Definition: False Decrease in Serum Sodium Due to Hyperlipidemia or Hyperproteinemia Causing Decreased Water Content Per Volume of Plasma
    • Concentration in Plasma is Decreased
    • Concentration in Water is Stable
  • Causes:
    • Hyperglycemia (DKA)
    • Hypertriglyceridemia from Pancreatitis
    • Obstructive Jaundice with Severe Hypercholesterolemia
  • Corrected Sodium = Na + 0.016 x (Glucose – 100)

Presentation

  • Nausea and Vomiting
  • Fatigue and Lethargy
  • Headache
  • Seizure
  • Coma

Sodium Deficit

  • Sodium Deficit = Total Body Water x (140 – Na)
  • Total Body Water:
    • Total Body Water (Males) = Weight (Kg) x 60%
    • Total Body Water (Females) = Weight (Kg) x 50%

Treatment

  • Acute Hyponatremia (< 48 Hours): Hypertonic (3%) Saline Boluses or Oral Sodium Replacement
  • Chronic Hyponatremia (> 48 Hours): Fluid Restriction (#1) and Diuresis
    • Consider Hypertonic (3%) Saline Boluses if Severe or Having Severe Symptoms (Seizure, Coma, etc.)
  • Goal Correction Rate: 6-8 mEq/L/Day
    • Avoid Correction Over 10-12 mEq/L Per Day
    • Risk for Osmotic Demyelination Syndrome with Over-Correction
      • Formerly Known as Central Pontine Myelinolysis (But Not Limited to Pons)
  • Management of SIADH: *See Syndrome of Inappropriate Anti-Diuretic Hormone (SIADH)