SIADH, DI, Cerebral Salt Wasting

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 bodys 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 kidneys
  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 lt 110 mEq/L, seizures, bulbar palsies,
  hypothermia, stupor, coma

7
SIADH lab values

• Serum Na lt 135 (Na is diluted by excessive free
  water re-absorption)
• Serum osmolality low, normal is 270
• Urine Na is inappropriately high, gt20 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
  wont 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 gt150-160
• High serum osmolality (normal 270)
• Urine Na lt 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, gt 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 dcd from hospital, most will still need
  oral Na supplementation for a period of time

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