SIADH

Syndrome of Inappropriate ADH Secretion (SIADH)

David Ray Velez, MD

Table of Contents

Definition
Causes
Diagnosis
Treatment

Definition

Definition: Inappropriately High Antidiuretic Hormone (ADH) Secretion

Antidiuretic Hormone (ADH)

  • Also Known As:
    • Vasopressin
    • Arginine Vasopressin (AVP)
  • Production:
    • Produced in Supraoptic and Paraventricular Nuclei of the Hypothalamus
    • Travels Down the Infundibulum and Then Secreted in the Posterior Pituitary
    • Secretion Stimulated by Increased Osmolality and Decreased Arterial Blood Volume
  • Vasopressin Receptors:
    • V-1 Receptor: Arterial Vasoconstriction (Increase Peripheral Vascular Resistance)
    • V-2 Receptor: Renal Water Resorption
    • V-3 Receptor: Mediates Factor VIII and vWF Release

Causes

Most Often Due to a Secondary Process

Causes

  • CNS Disturbances
    • Stroke
    • Hemorrhage
    • Infection
    • Trauma
  • Psychosis and Mental Illness
  • Surgery
  • Malignancy
    • Small Cell Lung Carcinoma (SCLC) – Most Common Malignant Cause
    • Extra-Pulmonary Small Cell Carcinomas
    • Head and Neck Cancers
  • Illicit Drugs (Ecstasy)
  • Medications
    • Diuretics
    • Chemotherapy
    • Antidepressants and Antipsychotics
    • ACE Inhibitors
    • Hormones
  • Pneumonia
  • HIV Infection
  • Idiopathic

Hereditary (Nephrogenic) SIADH: Gain of Function Mutation in the Renal V2 Receptors

Diagnosis

Generally a Clinical Diagnosis in the Critical Care Setting Based on Presentation and Serum/Urine Labs

Presentation

  • Hyponatremia
  • Low Urine Output (UOP)
  • Symptoms:
    • May Be Asymptomatic
    • Delirium
    • Confusion
    • Seizures

Laboratory Findings

  • Decreased Serum Sodium and Osmolality
  • Increased Urine Sodium and Osmolality

Diagnostic Criteria

  • Serum:
    • Decreased Serum Sodium (< 135 mEq/L)
    • Decreased Serum Osmolality (< 275 mOsm/kg)
  • Urine:
    • Increased Urine Sodium (> 40 mmol/L)
    • Increased Urine Osmolality (> 100 mOsm/kg)
  • Euvolemia – No Clinical Evidence of Volume Depletion
  • No Other Cause for Hyponatremia

Treatment

Primary Treatment: Fluid Restriction (< 800 mL/Day) and Treat Underlying Cause

Additional Treatment Options

  • Refractory Treatment:
    • Oral Salt Tablets
    • Furosemide (Lasix)
  • Severe Symptoms (Delirium, Seizure, etc):
    • Hypertonic Saline (3% NS) – Particularly if Acute Onset with Increased Risk for Fatal Cerebral Edema

*Caution Using IV Normal Saline (NS) – If Urine Osmolality is Greater than the Fluid Osmolality, it May Worsen Hyponatremia