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12.11.30 cPBL

Order of draw
  • Cultures
  • Clotting
  • Chemistry (no additives)
  • EDTA
    • Can give falsely low Ca, Mg
    • Also falsely low Alk-Phos, because it's an Mg-dept.reaction
  • Fluoride-oxylate

Sodium limits
  • Phone for help
    • Less than 125 mM
    • More than 150 mM
  • Life-threatening
    • Less than 115 mM
    • More than 160 mM
  • NB hypernatraemia can be just as dangerous as hyponatraemia
    • 40-50% mortality / 7X mortality increase
    • Although not corrected for co-morbidities

Excreting products of metabolism
  • Require minimum 600 ml of urine to enable excretion, in a healthy adult
    • Can be up to 1200 ml if sick
  • Calculate how much sodium your patient has had!
    • Antibiotics + fluids contribute LOADS of sodium
    • May require up to 4 litres of urine per day to excrete
  • HONK => Need extra water for excretion
  • Make sure you give enough water, or 5% dextrose
    • Even if they're diabetic, give dextrose (not significant in terms of blood glucose)

Causes of polyuria
  • Glucose
  • Hypercalcaemia
  • Hypokalaemia
  • Diabetes insipidus

Hyponatraemia
  • UTI can => Tubule dysfunction => Hyponatraemia
  • Drugs
    • SSRIs
    • Carbemazepine
  • Schizophrenia => Polydipsia ?
  • Some anaesthetics => ADH production
  • Glycine buffer
    • Used for irrigation in prostate, bladder, uterus surgery
      • As it doesn't conduct as well as saline?
    • Can get into blood => Hyponatraemia
  • Pseudohyponatraemia
    • Volume displacement causes raised blood volume and so apparently low sodium
    • But the [Na] in the aqueous phase is actually normal

Hepatorenal syndrome


Notes
  • Renal failure => Hypocalcaemia
    • Failure of vitamin D hydroxylation
    • => High PTH
    • => Renal bone disease
  • Plasma sample
    • Lithium heparin
    • Orange / Green tube
    • Doesn't clot => No risk of potassium release from platelets
  • Be very wary of using half- or twice- normal saline

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