Presentation

What does SIADH stand for?

• Syndrome of Inappropriate Antidiuretic Hormone secretion

• Characterized by excess ADH

• Leads to water retention and dilutional hyponatremia

How does antidiuretic hormone (ADH) normally function in the body?

• ADH allows the kidneys to hold onto water

• Released by the posterior pituitary

• Normally secreted when:

  • Dehydrated

  • Hypovolemic

  • Hypernatremic

• Results in:

  • ↓ urine output

  • ↑ urine concentration

What is the fundamental problem in SIADH?

• Too much ADH is released inappropriately

• Occurs despite normal or excess fluid volume

• Causes kidneys to:

  • Retain free water

  • Dilute serum sodium

• Leads to fluid volume overload without edema initially

Why are patients with SIADH hyponatremic?

• Excess ADH → water retention

• No sodium retention

• Serum sodium becomes diluted

• Results in dilutional hyponatremia

How does SIADH affect urine concentration?

• Urine becomes inappropriately concentrated

• Despite low serum osmolality

• Kidneys continue reabsorbing water due to ADH

What is the key difference between SIADH and Diabetes Insipidus (DI)?

• SIADH:

  • Too much ADH

  • Water retention

  • Hyponatremia

  • Concentrated urine

• DI:

  • Too little or ineffective ADH

  • Excessive water loss

  • Hypernatremia

  • Dilute urine

What are the hallmark clinical manifestations of SIADH?

• Dilutional hyponatremia

• Neurologic symptoms due to cerebral edema

• Decreased urine output

• Weight gain

• Signs of fluid volume overload

What neurologic symptoms are seen in SIADH and why?

• Caused by low serum sodium

• Water shifts into brain cells → cerebral edema

• Symptoms include:

  • Confusion

  • Headache

  • Lethargy

  • Seizures

  • Decreased LOC

  • Coma (severe cases)

What gastrointestinal symptoms are commonly seen in SIADH?

• Nausea

• Vomiting

• Abdominal pain

• Anorexia

• Often early and nonspecific

What cardiovascular and respiratory findings suggest SIADH?

• Tachycardia

• Bounding pulses

• Jugular venous distention (JVD)

• Crackles in lungs

• Dyspnea

• Signs of fluid volume overload

What serum laboratory findings are expected in SIADH?

• Low serum sodium (<135 mEq/L)

• Low serum osmolality (<275 mOsm/kg)

• Dilutional state due to excess free water

What urine laboratory findings are characteristic of SIADH?

• High urine osmolality (>100 mOsm/kg)

• High urine sodium (>40 mEq/L)

• Urine remains concentrated despite low serum osmolality

Why is urine sodium high in SIADH despite hyponatremia?

• ADH causes water retention, not sodium retention

• Sodium continues to be excreted

• Results in concentrated urine with high sodium

What are common causes of SIADH related to the CNS?

• Traumatic brain injury

• Stroke

• Subarachnoid hemorrhage

• Meningitis

• Encephalitis

• Brain tumors

What malignancies are strongly associated with SIADH?

• Small cell lung carcinoma

• Produces ectopic ADH

• Most classic cancer cause of SIADH

What pulmonary conditions can trigger SIADH?

• Pneumonia

• Tuberculosis

• Acute respiratory failure

• Hypoxia stimulates ADH release

What medications are known to cause SIADH?

• SSRIs

• Antiepileptics (e.g., carbamazepine)

• Chemotherapy agents

• Anesthesia

• Postoperative stress

What is the first-line treatment for SIADH?

• Fluid restriction

• Typically 500–1000 mL/day

• Reduces free water intake below retained volume

Why are patients with SIADH placed on fluid restriction?

• They already have too much water

• Adding fluids worsens hyponatremia

• Restriction helps raise serum sodium

What pharmacologic treatments may be used for SIADH?

• Salt tablets → increase solute intake

• Loop diuretics (furosemide) → promote free water excretion

• Vasopressin receptor antagonists:

  • Tolvaptan

  • Promote aquaresis (water loss without sodium loss)

When is hypertonic saline used in SIADH?

• Severe symptoms:

  • Seizures

  • Profound confusion

  • Coma

• 3% NaCl

• Must be given slowly and carefully

Why must sodium correction be done slowly in SIADH?

• Rapid correction risks:

  • Osmotic demyelination syndrome

• Requires frequent sodium monitoring

What are priority nursing responsibilities in SIADH?

• Strict intake and output monitoring

• Daily weights (same time, same conditions)

• Monitor neurologic status

• Assess for fluid overload

• Monitor serum sodium closely

What patient education is essential for SIADH?

• Importance of fluid restriction

• Recognizing symptoms of hyponatremia

• Medication adherence

• Dietary sodium guidance

• When to seek medical attention

What signs indicate worsening SIADH that must be reported immediately?

• New confusion

• Headache

• Seizures

• Sudden weight gain

• Decreased urine output

• Worsening hyponatremia