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SIADH, DI, Cerebral Salt Wasting

SIADH, DI, Cerebral Salt Wasting. By Tracy Merrill MD Feb 24, 2003. SIADH:. = Syndrome of Inappropriate ADH Secretion Definition: levels of ADH are inappropriately elevated compared to body’s low osmolality, and ADH levels are not suppressed by further decreases in blood osmolality.

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SIADH, DI, Cerebral Salt Wasting

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  1. SIADH, DI, Cerebral Salt Wasting By Tracy Merrill MD Feb 24, 2003

  2. SIADH: • = Syndrome of Inappropriate ADH Secretion • Definition: levels of ADH are inappropriately elevated compared to body’s low osmolality, and ADH levels are not suppressed by further decreases in blood osmolality.

  3. SIADH: causes • Irritation of CNS: meningitis, encephalitis, brain tumors, brain hemorrhage, hypoxic insult, trauma, brain abscess, Guillain Barre, hydrocephalus • Pulmonary disorders: pneumonia, asthma, positive end expiratory pressure ventilation, CF, TB, pneumothorax

  4. SIADH: causes continued • Drugs: vincristine, vinblastine, opiates, carbamazepime, cyclophosphamide • Unregulated tumor production of ADH-like peptides: oat cell lung carcinoma for example, Ewings sarcoma, carcinoma of duodenum, pancreas, thymus

  5. SIADH: function of ADH • = antidiuretic hormone = vasopressin • ADH is made in the supra-optic nuclei in the hypothalamus, stored in the posterior pituitary • Normally released into the bloodstream when osmo-receptors detect high plasma osmolality • At the kidney, attaches to receptors in the collecting ducts, opens up water channels • Water is passively reabsorbed along the kidney’s medullary concentration gradient

  6. SIADH: signs and symptoms • Decreased/low urine output • Signs of hyponatremia: lethargy, apathy, disorientation, muscle cramps, anorexia, agitation • Signs of water toxicity: nausea, vomiting, personality changes, confused, combative • If Na < 110 mEq/L, seizures, bulbar palsies, hypothermia, stupor, coma

  7. SIADH: lab values • Serum Na < 135 (Na is diluted by excessive free water re-absorption) • Serum osmolality low, normal is ~ 270 • Urine Na is inappropriately high, >20 mmol/L, actually losing Na in urine instead of retaining it • Urine osmolality is inappropriately high, can range b/t 300-1400 mosm/L • CVP is high from free water retention

  8. SIADH: treatment • Fluid restriction, ¾ maintenance • If symptomatic, may actually need to replace NaCl, can use hypertonic saline for example: 300cc/m2 of 1 ½ % NS • Diuretics such as lasix • Treat underlying disorder, for example usually resolves after removal of lung carcinomas

  9. SIADH: treatment cont… • Demeclochlorotetracycline, blocks ADH receptors in the renal collecting ducts • In severe cases, hemodialysis • Warning, if increase Na too fast, at risk for pontine myelinolysis • Max correction of 15mEq in 24 hours

  10. DI = Diabetes Insipidus • Definition: inability to effectively conserve urinary water • Central: ADH not made or not released in the hypothalamic-pituitary axis • Nephrogenic: ADH is released but not detected by the receptors in the kidney collecting ducts, often a sex-linked recessive condition, also due to renal pathology, electrolyte disorders, drugs

  11. Central DI: causes • Head trauma • Brain neoplasms • Congenital CNS defects • CNS infections • CNS hypoxia • ADH secretion also decreased by certain drugs: EtOh, demerol, MSO4, dilantin, barbiturates, glucocorticoids

  12. DI: • Make sure distinguish DI from conditions in which the presence of non-absorbable, osmotically active solutes in the renal tubules prevent water re-absorption. • Example: glucose loss in the urine of diabetics will decrease the tubule- medullary concentration gradient and even though ADH is there, water won’t get passively reabsorbed

  13. Central DI: signs/symptoms • Polyuria • Dehydration, may not be readily apparent b/c of hyper-osmolarity, fluid shifts from cells to intravascular spaces and maintains blood pressure, CVP • Weight loss is a better measure of fluid status

  14. Central DI: Lab values • Hypernatremia, Na >150-160 • High serum osmolality (normal 270) • Urine Na < 20 mmol/L • Low urine osmolality (very dilute urine)

  15. Central DI: treatment • Increase po or IV free H20 consumption, use hypotonic saline • Volume replacement cc for cc • Vasopressin/ ADH administration (bolus or drip 1.5-2.5 mU/kg/hr) • Of course, treat underlying cause

  16. Cerebral Salt Wasting • Causes: CNS damage • Closed head injury • CNS surgery • CNS tumors • CNS infections, meningitis

  17. Cerebral Salt Wasting • Signs/symptoms: • Polyuria • Wt loss • Dehydration/hypovolemia • Hypotension • Low CVP

  18. Cerebral Salt Wasting • Lab values: • Hyponatremia due to excessive renal Na loss • High urine Na, > 20 mmol/L • Increased plasma ANP, atrial natriuretic peptide, b/c of low volume status • Inappropriately normal or low aldosterone and ADH levels despite high ANP

  19. Cerebral Salt Wasting • Treatment: • Volume for volume replacement of urine Na losses • When dc’d from hospital, most will still need oral Na supplementation for a period of time

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