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Home | CCC | Hypophosphataemia

Hypophosphataemia

by Dr Chris Nickson, last update April 22, 2019

OVERVIEW

  • important intracellular anion
  • 85% is stored in bone as hydroxyapapitie crystals, 14% in soft tissues, 1% in blood
  • intracellular concentration = 100mmol/L
  • plasma concentration = 0.8-1.3mmol/L

-> thus hypophosphataemia describes total body depletion

Hypophosphataemia = < 0.8

MILD – 0.65-0.8
MODERATE – 0.32-0.65
SEVERE – actions on intestine, kidneys and bone

  • PTH -> increase in phosphate and Ca2+ release from bone, but increases excretion in kidney by inhibiting reabsorption in the proximal tubule
  • vitamin D from kidneys acts on jejunum to increase absorption of Ca2+ and phosphate

FUNCTIONS – many!

  • ATP
  • nucleic acids
  • phospholipids
  • enzymatic co-factors
  • cGMP
  • cAMP
  • 2, 3 DPG
  • enzymes in glycolytic pathway
  • buffer in maintenance of plasma pH
  • immune system integrity
  • coagulation cascade

CAUSES

Hypophosphataemia

  • intake: malnutrition, phosphate binders, vitamin D, malabsorption, TPN
  • redistribution: refeeding syndrome, insulin in DKA
  • output:
    urinary – diuretics, osmotic diuresis, hyperparathyroidism, proximal tubular dysfunction (Fanconi’s syndrome)
    non-urinary –
    -> upper GI
    -> mid GI
    -> lower GI – diarrhoea
    -> other – sweat, burns, sepsis, bleeding

HISTORY

  • look for symptoms of hypophosphataemia + cause (renal loss, intake, redistribution into cells, catabolic state)
  • SOB
  • ventilator dependence
  • weakness
  • altered mental state
  • heart failure symptoms
  • shock

EXAMINATION

  • CVS: reversible dilated cardiomyopathy, inotrope requirement
  • RESP: respiratory failure, ventilator dependence, left shift of oxy-Hb dissociation curve
  • NEURO: altered mental state, weakness, gait disturbance, paraesthesiaes
  • HAEM: haemolysis, disorders of WCC function,
  • ENDO: bone demineralisation
  • MUSKULO: rhabdomyolysis

INVESTIGATIONS

  • aimed at quantifying severity and finding cause
  • phosphate, Ca2+, K+, Mg2+
  • ECG

MANAGEMENT

  • feed adequately (caution in refeeding syndrome)
  • if phosphate 0.65-0.89 give oral phosphate
  • IV phosphate:

-> KH2PO4 – 10mmol of phosphate and 10mmol of K in 10mL
-> NaKH2PO4 – 13.4mmol of phosphate, 21.4mmol Na+, 2.6mmol K in 20mL

  • administer 1 ampoule over 1 hour
  • bewared of phosphate administration in renal failure
  • monitor for hyperphosphataemia, hypocalcaemia, hypotension, tetany and ECG changes

References and Links

  • CCC – Hyperphosphataemia
  • CCC – Hyperphosphataemia Mind Map (PDF)
  • CCC – Hypophosphataemia
  • CCC – Hypophosphataemia Mind Map (PDF)

CCC 700 6

Critical Care

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About Dr Chris Nickson

An oslerphile emergency physician and intensivist suffering from a bad case of knowledge dipsosis. Key areas of interest include: the ED-ICU interface, toxicology, simulation and the free open-access meducation (FOAM) revolution. @Twitter | INTENSIVE| SMACC

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