ASK A VET™
Phosphate Supplementation Calculator
Hypophosphataemia in DKA, refeeding & critical patients — dogs & cats
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Patient & Order
0.01 conservative0.03 standard0.12 aggressive
Advanced: total potassium safety & bag mixing
Added to the potassium from phosphate to check the 0.5 mEq/kg/hr ceiling.
Enter the fluid rate to get "mL of salt to add to this bag". Leave 0 to skip.
Result
Add to phosphate-free fluids
— mL total
Phosphate rate
—
mmol/hr
Total phosphate
—
mmol over run
Salt rate
—
mL/hr
Potassium load
—
mEq/kg/hr
Potassium from phosphate—
Existing KCl in fluids—
Total potassium rate—
Ceiling: 0.5 mEq/kg/hr potassium (maximum safe infusion rate).
How to use it — clinical notes
When to supplement
Treat phosphorus < 1.5 mg/dL (< 0.5 mmol/L), or < 2.0 mg/dL with clinical signs or ongoing insulin therapy in DKA. Insulin drives phosphate intracellularly, so DKA patients often crash their phosphorus 12–24 h into treatment even when the initial level is normal — recheck it.
Why it matters
Severe hypophosphataemia causes haemolysis, muscle weakness (including respiratory), rhabdomyolysis, and neurological signs. Cats are particularly prone to haemolytic anaemia.
Dosing
START 0.03 Begin at 0.03 mmol/kg/hr. Reserve 0.06–0.12 mmol/kg/hr for severe or refractory cases with close monitoring. Titrate to effect — this is a range, not a fixed dose.
Recheck
Measure phosphorus every 6 hours during a CRI. Stop supplementation once phosphorus is > 2.0 mg/dL (> 0.65 mmol/L) to avoid overshoot and hyperphosphataemia.
Never mix with calcium
Do not add phosphate to calcium-containing fluids (Hartmann's / lactated Ringer's) — calcium phosphate precipitates. Run in 0.9% saline or another calcium-free carrier.
Watch the potassium
Potassium phosphate delivers 4.4 mEq K⁺ per mL. Count it toward the patient's total potassium and keep the combined rate ≤ 0.5 mEq/kg/hr. Reduce the KCl accordingly.
Monitor for over-correction
Risks: hypocalcaemia, hyperphosphataemia, hyperkalaemia (K salt) or hypernatraemia (Na salt), and metastatic soft-tissue mineralisation. Avoid phosphate in oliguric/anuric renal failure and hypercalcaemia.
Product concentrations vary
This tool assumes 3 mmol PO₄/mL. Check your vial label — always confirm concentration before drawing up.
Track phosphorus, electrolytes and DKA cases in one place.
ASK A VET™ stores bloods, trends and treatment sheets so the next recheck is one tap away — for clinics and owners.
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Disclaimer. This calculator is veterinary clinical decision-support for qualified professionals. It does not replace clinical judgement, current formularies, or product labelling. Verify every dose, concentration and compatibility against your own references before administration. Not for use in human medicine. © ASK A VET™ · Dr Duncan Houston.