Fluids, Electrolytes & Nutrition: Anti-Diuretic Hormone (ADH)

Anti-Diuretic Hormone (ADH)

Other Names

  • Vasopressin
  • Arginine Vasopressin (AVP)

Function

Syndrome of Inappropriate Anti-Diuretic Hormone Syndrome (SIADH)

Definition

  • Definition: Inappropriately High ADH Secretion

Causes

  • CNS Disturbance (Stroke, Hemorrhage, Infection or Trauma)
  • Psychosis
  • Surgery
  • Small Cell Lung Carcinoma
  • Medications
    • Diuretics
    • Chemotherapy
    • Antidepressants & Antipsychotics
    • Illicit Drugs (Ecstasy)
    • ACE Inhibitors
    • Hormones
  • Idiopathic

Presentation

  • Hyponatremia
  • Low Urine Output (UOP)

Diagnostic Criteria

  • Decreased Serum Osmolality (< 275 mOsm/kg)
  • Increased Urine Osmolality (> 100 mOsm/kg)
  • Increased Urine Sodium (> 20 mmol/L)
  • Euvolemia
  • No Other Cause for Hyponatremia

Treatment

  • Primary Treatment: Fluid Restriction & Treat Underlying Cause
  • Consider Hypertonic Saline if Severe, Symptomatic or Refractory
    • Particularly Consider if Acute Onset (< 48 Hours) – Increased Risk of Fatal Cerebral Edema

Diabetes Insipidus (DI)

Definitions

  • Central DI: Low ADH Secretion
  • Nephrogenic DI: Poor Renal Response to ADH

Causes

  • Central DI:
    • Idiopathic – Most Common Cause of DI Overall
    • Congenital (Hypothalamus Malformations)
    • Surgery/Neurosurgery
    • Trauma
    • Hypoxic Brain Injury
    • Autoimmune
    • Sarcoidosis
    • Malignancy
    • Anorexia Nervosa
  • Nephrogenic DI:
    • Idiopathic
    • Hereditary (AVPR2 Receptor Mutation)
    • Medications:
      • Lithium
      • Antibiotics
      • Antineoplastic Medications
    • Renal Disease
    • Sickle Cell Disease
    • Pregnancy
    • Electrolyte Disturbances (Hypokalemia & Hypercalcemia)
    • *Most Common Cause of Nephrogenic DI Severe Enough to Produce Polyuria: Chronic Lithium Use or Hypercalcemia

Presentation

  • Hypernatremia
  • High Urine Output (UOP)
  • Symptoms:
    • Polydipsia
    • Polyuria
    • Nocturia

Diagnosis

  • First Step: Rule Out Hyperglycemia & Other Obvious Osmotic Causes of Polyuria
  • Laboratory Findings:
    • Hypernatremia
    • Increased Serum Osmolality
    • Decreased Urine Osmolality (< 200 mOsm/kg)
    • High Urine Output (> 3 L/Day)
  • Water Deprivation Test
    • *Rarely Used in the Critical Care Setting
    • Test: Water is Deprived for 4-18 Hours with Serial Plasma/Urine Osmolality
      • Stop Once 5% of Body Weight is Lost or Two Urine Sample Show < 30 mOsm/kg
      • Then Check ADH & Give 1 mcg Desmopressin (DDAVP)
      • Then Check Urine Osmolality at 30- & 60-Minutes
    • Interpretation:
      • Psychogenic Polydipsia
        • Urine Osmolality > Plasma Osmolality
        • Urine Osmolality Increases < 10% After ADH
      • Central DI
        • Urine Osmolality < Plasma Osmolality
        • Urine Osmolality Increases > 50% After ADH
      • Nephrogenic DI
        • Urine Osmolality < Plasma Osmolality
        • Urine Osmolality Increases < 50% After ADH

Classification

  • *Based on Desmopressin (DDAVP) Trial Over 2 Hours
  • Nephrogenic:
    • Complete Nephrogenic DI: No Elevation in Urine Osmolality (< 300 mOsm/kg)
    • Partial Nephrogenic DI: Small (≤ 45%) Elevation in Urine Osmolality with Level < 300 mOsm/kg
  • Central:
    • Complete Central DI: Rise in Urine Osmolality > 100%
    • Partial Central DI: Rise in Urine Osmolality 15-50% with Level > 300 mOsm/kg

Treatment

  • Central DI:
    • Acute/Severe: DDAVP (Desmopressin)
      • Dosing: 2 mcg IV Every 12 Hours
    • Mild-Moderate Symptoms: Low-Solute Diet (Low-Sodium & Low-Protein)
      • May Also Consider Thiazide Diuretics
  • Nephrogenic DI:
    • Initial Treatment: Low-Solute Diet (Low-Sodium & Low-Protein)
    • If Fails: Add Thiazide Diuretic (Hydrochlorothiazide)
    • If Still Fails: Add Amiloride
    • Also Treat Any Underlying Causes