Neurosurgery notes/Other specialities/ITU/Endocrine/Hyponatraemia/CSW

CSW

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Hyponatraemia

General

  • Cerebral salt wasting (CSW)
  • Definition: hypovolemic hyponatremia with diuresis and natriuresis
  • Extracellular volume low
  • High K
  • Often heralds the onset of cerebral vasospasm

Mechanism

  • Unknown
  • ?? Rise in ANF (atrial natriuretic factor) in ventricles → urinary loss of Na

Treatment:

  • Keep well hydrated: NS 125ml/hr
  • DO NOT give furosemide
  • Oral Na
  • Hypertonic saline → severe cases
  • Fludrocortisone
    • Acts on renal tubule to increase sodium absorption
    • 0.2mg IV/PO QDS
    • Has significant complication
      • Pulmonary oedema
      • Hypokalaemia
      • HTN
  • Urea:
    • Can be given to CSW and SIADH—> no need to first do
    • Suspect it works by Urea enter urine —> pulls water into urine —> increasing Water loss relative to Na loss
    • 0.5g/kg (dissolve 40mg in 100ml of NS) IV over 30-60mins 8hrsly
    • Use NS +20mmol of KCL/L at 2ml/kg/hr

DDx

  • Although it can be difficult to evaluate volume status clinically, particularly when endeavouring to separate mild hypovolemia from eunatremia, cerebral salt wasting is usually characterised by profound natriuresis, diuresis, and marked volume depletion
Parameter
CSW
SIADH
Plasma volume
↓ (< 35 ml/kg)
↑ or WNL
Salt balance
negative
variable
Signs & symptoms of dehydration
present
absent
Weight
↓
↑ or no Δ
PCWP
↓ (< 8 mm Hg)
↑ or WNL
CVP
↓ (< 6 mm Hg)
↑ or WNL
Orthostatic hypotension
+
±
Hematocrit
↑
↓ or no Δ
Serum osmolality
↑ or WNL†
↓
Ratio of serum BUN]:[creatinine]
↑
WNL
Serum [protein]
↑
WNL
Urinary [Na+]
↑↑
↑
Serum [K+]
↑ or no Δ
↓ or no Δ
Serum [uric acid]
WNL
↓
  • Abbreviations: ↓ = decreased, ↑ = increased, ↑↑ = significantly increased, WNL = within normal limits, no Δ = no change, []= concentration, + = present, ± = may or may not be present
      • † in reality, serum osmolality is usually ↓ in CSW
  • There is no idea why SIADH has high urinary Na
  • The presence of elevated plasma BNP concentrations could not be regarded as a reliable predictor of either blood volume status or the development of hyponatremia