SIADH, DI, Cerebral Salt Wasting

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SIADH, DI, Cerebral Salt Wasting

• By Tracy Merrill MD
• Feb 24, 2003

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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.

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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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

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Cerebral Salt Wasting

• Causes CNS damage
• Closed head injury
• CNS surgery
• CNS tumors
• CNS infections, meningitis

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Cerebral Salt Wasting

• Signs/symptoms
• Polyuria
• Wt loss
• Dehydration/hypovolemia
• Hypotension
• Low CVP

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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

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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

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