Hypophosphataemia

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 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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