Hypophosphatemia

Currently, I have been seeing patients with hypophosphatemia, and for a few, this has been persistent despite ongoing replacement..

Causes of hypophosphatemia:

  • Acute respiratory alkalosis
    • Rise in intracellular pH stimulates phosphofructokinase activity which in turn stimulates glycolysis → ↑ in demand for phosphate, which is driven intracellularly to form glycolytic intermediate metabolites
      • A similar phenomenon is observed with an increase in intracellular pH, which occurs in metabolic alkalosis
    • Extreme hyperventilation (PCO2 <20mmHg) in normal subjects can also lower serum phosphate concentrations to below 0.32 mmol/L
    • References:
  • Refeeding syndrome
    • Concern of referring syndrome in malnourished, alcohol abuse
  • Stress-induced
    • Dieticians are able to calculate patients’ metabolic needs and assess if the feeds are sufficient in meeting this. Had a patient with status epilepticus with persistently low phosphate levels despite frequent replacement. Dietician calculated her needs and found that it significantly exceeded her feeds. After replacing feeds (and also accounting for the fact that patient is on propofol), phosphate levels were generally WNL
  • Increased losses (e.g. diarrhea, large NG loss)
  • Diabetic Ketoacidosis

Drug causes of hypophosphatemia:

  • Phosphate binders – e.g. calcium supplements
  •  ↑ urinary excretion – e.g. carbonic anhydrase inhibitors, bisphosphonates, corticosteroids
  • Cause vitamin D deficiency or resistance – e.g. phenytoin, phenobarbital
  • IV iron administration
  • Acetaminophen poisoning
  • References: Medicationinducedhypophos

Symptoms of hypophosphatemia:

  • Respiratory failure
  • Cardiac abnormalities
  • CNS dysfunction
  • Difficulty weaning from venilation

Management:

  • Address underlying causes
  • Supplement phosphate
    – e.g. NaPO4 IV 15 mmol (=20mmol Na), KPO4 IV 15 mmol (= 22 mmol K+)

    • ICU Rapid Resource at VGH: 20-40 mmol PO4/day
  • Monitor serum levels at least daily
  • Monitor renal function daily – if AKI, risk of accumulation!
  • Monitor for hyperphosphatemia (symptoms: paresthesia, flaccid paralysis, mental confusion, hypertension, cardiac arrhythmias, tissue calcification)
Advertisements