Syndrome of inappropriate antidiuretic hormone secretion

Syndrome of inappropriate antidiuretic hormone secretion

Anesthetic relevance
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Signs and symptoms
Diagnosis
Treatment
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Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a condition in which excess anti-diuretic hormone (ADH) - also known as vasopressin - is produced. Downstream effects include 1. retention of excess water which can lead to cerebral edema/seizures/coma/death, 2. hyponatremia which can lead to arrhythmias and - if sodium corrected is attempted - potentially iatrogenic Osmotic demyelination syndrome (OSD)/Central pontine myelinolysis (CPM).

Anesthetic implications

Preoperative optimization

• Evaluate overall sodium trend
  • Most anesthesiologists would consider delaying case if sodium x<130
  • Ideally sodium should be corrected to normal limits or at least stabilized or trending towards correction prior to surgery
    • Uncorrected sodium levels merits discussion with internal medicine and surgery.

Intraoperative management

• Serial ABG to monitor serum sodium
  • concern for overly rapid correction - potentially leading to OSD or CPM.
    • Maintain sodium correction to 0.5mmol/L/hr with goal of 4-8mmol/L in 24 hours
• Avoid hypotonic fluids
  • half normal saline
  • dextrose in water
  • LR - can consider but requires very close monitoring of sodium levels
• Preferred fluids
  • Hypertonic saline

Pathophysiology

General Mechanism of Action of ADH

• ADH is a hormone produced by the hypothalamus, then stored and released via the posterior pituitary gland
• ADH is responsible for mechanisms pertaining to water retention via upregulation of aquaporin channels in renal nephrons to increase water re-absorption. ADH's main effect leads to increased fluid volume while decreasing serum sodium concentration and decreasing urinary output volume.

Consequences

Causes

• Cancer
  • Brain tumors
  • Small Cell Lung Cancer
  • Lymphoma
• Central Nervous System
  • Brain Surgery - especially pituitary gland surgery
  • Brain tumors
  • Meningitis
  • Encephalitis
  • Brain trauma
  • Hypopituitarism
  • Stroke
• Guillain-Barre
• Heart Failure
• Lung Pathology
  • Pneumonia
• Medications
  • SSRIs
  • Anti-neoplastic drugs
  • Anti-psychotics
• Acute stressors
  • pain
  • Nausea
• Hypothoridism
• HIV infection

Signs and symptoms

Symptoms

• Cerebral
  • Altered mental status
  • Seizures
  • Loss of balance/coordination
  • Coma
• GI
  • Nausea
  • Emesis
• Musculoskeletal
  • Muscle cramps
  • Muscle weakness

Diagnosis

• Hyponatremia (serum) x< 135 mEq/L
• High urine osmolality: 100+ mOsm/kg
• High Urine sodium levels 40+ mEq/L
• Euvolemic or fluid overload state

Treatment

• Overall treatment is to remove excess water from the body
• Diuretics
• H20 restriction
• Demeclocycline (off-label)
  • a tetracycline antibiotic that is used off-label to treat SIADH by decreasing renal response to ADH
• Treat inciting etiology

Epidemiology

Risk factors for SIADH

• Increasing age
• Hospitalization
• Lung cancer
• Cerebral pathology/manipulation