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

Critical Care

Compendium

…more CCC

Chris Nickson

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.

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