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 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 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

20. DI SIADH CSW CVP Urine Output polyuric decreased Serum Na high low
Urine Na
Serum osm
Can be low or normal
Urine osm
CVP
Can be normal or low