Flashcards in SIADH Deck (66)
What does SIADH/SIAD stand for?
- Syndrome of Inappropriate Secretion of Antidiuretic Hormone
- Syndrome of Inappropriate Antidiuresis
What is osmolality?
A measure of the solute (Na, K, Cl) concentration in a unit of water.
What is anit-diuretic hormone (ADH)?
- Also called Arginine Vasopressin.
- Produced by the hypothalamus and stored in the posterior pituitary gland.
What are the 2 primary functions of ADH?
- Regulates water retention in Kidneys
- Vascular constriction
SIADH is a result from?
- Hyponatremia and hypo-osmolality
- Resulting from inappropriate, continued secretion or action of ADH despite normal or increased plasma volume, which results in impaired water excretion.
Hyponatremia is a result of what?
Hyponatremia is a result of an excess of water rather than a deficiency of sodium.
In general, SIADH is due to what 3 things?
1. Elevated levels of ADH
2: Water retention
3: Loss of or dilution of certain electrolytes or solutes (Na, K, Cl)
What is the most important effect of ADH?
Conserve water by reducing water loss through the kidneys.
Higher ambient temperatures causes what?
Loss of water via sweat.
Increased plasma osmolarity causes what?
A concentration of blood solutes.
What is the pathophysiology of ADH (Vasopressin)?
- Synthesized in the hypothalamus .
- Stored in the posterior pituitary.
- Endocrine negative feedback mechanism from Osmoreceptors in hypothalamus.
What are the kidneys response to ADH?
- ADH increases the permeability of the distal convoluted tubules in the nephrons
- This allows for water reabsorption, thus preventing water loss.
ADH activity dilutes what?
ADH activity dilutes blood levels of solutes.
- water reabsorption NOT solute absorption.
What are the CNS response to ADH?
- Dysarthria: Slurred or slow speech
- Coma (from brain swelling)
Most cases of SIADH have what etiology? and what are most caused by?
- Cancer etiology
- 70% are caused by Small Cell Lung CA .
Where are some ADH producing tumors?
- Carcinomas (Small Cell)
- Thymus gland
What are common causes of SIADH in pulmonary disease?
- Lung Abscess
What are the CV responses to ADH?
- ADH increases peripheral vascular resistance and thus increases arterial blood pressure.
- Becomes an important compensatory mechanism for restoring blood pressure in various forms of hypovolemic shock
What are the forms of hyopvolemic shock?
What are common causes of SIADH in CNS disorders?
- Meningitis / Encephalitis
- Brain Abscess
- Intracranial hemorrhage
- Cerebral aneurysm
- Subdural bleeds
- Head trauma
- Vascilitis: Lupus
What drugs cause SIADH?
- Antibiotics: Ciprofloxin
- SSRI’s: Fluoxetine (Prozac)
- Carbamazepine (Tegretol):
- Chlorpropamide: Sulphonylurea
- Cyclophosphamide: tx of Lymphoma
What level of sodium is indicative of hyponatremia?
What are sxs of sodium <130?
- Weight gain
What are sxs of sodium <115?
- Mental status changes
What are neurological sxs of SIADH?
- Personality changes
- Decreased Reflexes
What are GI sxs of SIADH?
- Muscle cramps
What are medical comorbidities of SIADH?
- Liver failure
- Renal failure
Hyponatremia is recognized only secondary to the comorbidity sxs such as what?
The recognition of SIADH is entirely what? and pts may develop clinical sxs d/t what?
- Entirely incidental.
- Sxs may be d/t the cause of hyponatremia or hyponatremia itself.