Hypophosphatemia¶
Peter Thorne
Background¶
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Required for metabolic pathways (ATP production!)
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Most renal reabsorption occurs in proximal tubule via sodium-phosphate cotransporter
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Common causes
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Internal redistribution, reduced intestinal absorption
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Refeeding syndrome
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Alkalemia
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Phos binders on purpose or inadvertently (calcium, aluminum, magnesium antacids)
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Excessive loss (diarrhea, CRRT, increased urinary excretion)
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Proximal tubular dysfunction such as in Fanconi Syndrome
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Hyperparathyroidism causes renal phos wasting
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Post-parathyroidectomy leading to hungry bone syndrome
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Vitamin D deficiency or resistance
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Presentation¶
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Mild Hypophosphatemia (serum >2.0) rarely symptomatic
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PO4-3\< 2.0: Muscle weakness
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PO4-3\< 1.0: Heart failure, respiratory failure, rhabdomyolysis, seizures
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Failure to wean from ventilator
Evaluation¶
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Urine PO4-3 level if cause not readily apparent
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Calculate Fe PO4-3 ([U PO4-3 x PCr x 100]/[P PO4-3x UCr])
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Fe PO4-3 \< 5% = normal renal response to hypophos: redistribution or ↓ absorption
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Fe PO4-3 > 5% = renal phos wasting
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Management¶
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Caution replacing in pts with impaired renal function: start with half suggested dose
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If K+ > 4 and patient requires IV repletion, may need to use sodium PO4-3 in place of K+ PO4-3 IV; po preferred unless severe or symptomatic, or patient cannot take po
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K-Phos neutral: oral, each 250mg tablet has 8 mmol of PO4-3 and 1.1mEq of K+
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K+ PO4-3: IV, each mL has 3mmol PO4-3, 4.4 meq K+
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Na+ PO4-3: IV, each mL has 3mmol PO4-3
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PO4-3>1.5: PO: 40 – 80 mmol K+Phos neutral (aim for 1 mmol/kg) divided into 3-4 doses/day
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PO4-3 1.25 - 1.5: oral 100 mmol K+ PO4-3neutral in 3-4 divided doses if asymptomatic
- IV: 30 mmol K+ PO4-3over 6 hours (aim for 0.4mmol/kg) if symptomatic
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PO4-3\<1.25: IV: 80mmol K+Phos over approximately 12 hours (aim for 0.5mmol/kg)
- Check serum PO4-3 2-12 hrs after last dose of PO4-3 to determine if additional needs