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)
Critical Care
Compendium
Leave a Reply