Electrolytes & Fluids

Hypophosphatemia / KPhos CRI

IV potassium phosphate CRI for hypophosphatemia in dogs and cats. Enter serum P and body weight; returns a KPhos rate from a 5-tier sliding scale and surfaces the potassium load KPhos contributes so total K supplementation (including any concurrent KCl) stays under the 0.5 mEq/kg/hr cardiac-safety ceiling.

KPhos: 4.4 mEq K + 3 mmol P / mL

K from KPhos counts toward the 0.5 mEq/kg/hr ceiling. Standard KPhos delivers 4.4 mEq of potassium per mL alongside the phosphate. If the patient is on a concurrent KCl CRI, the K contribution from KPhos must be subtracted from the planned KCl rate. The result panel surfaces total K delivery and the headroom remaining for KCl.
Severe hypophosphatemia causes hemolysis. Acute intravascular hemolysis is the most life- threatening complication of severe hypophosphatemia. Respiratory muscle weakness, cardiac dysfunction, and CNS depression are also possible. Recheck serum P every 4–6 hours during active KPhos therapy.
Dilute before infusion. Never give KPhos undiluted IV. Dilute into 0.9% NaCl, LRS, or Plasma-Lyte. Calcium-containing fluids will precipitate as calcium phosphate, verify line compatibility.

Using this in DKA?

Hypophosphatemia affects ≈48% of dogs after starting DKA therapy; insulin shifts P intracellularly. Check P every 4–12 hours during DKA management. The K-from-KPhos / KCl interaction matters most in this setting because most DKA patients are also on a KCl CRI per the hypokalemia sliding scale. See the DKA management hub for the full workflow.

Species

Dog Cat

Patient weight

lb kg

Serum phosphorus (mg/dL)

Reference range typically 2.5–6.0 mg/dL (adult dogs and cats). Bands: ≥2.0 not indicated · 1.5–2.0 mild · 1.0–1.5 moderate · 0.5–1.0 severe · <0.5 critical.

Concurrent KCl rate (mEq/kg/hr) — if patient is on KCl CRI

If the patient is on a separate KCl CRI per the hypokalemia sliding scale, enter that rate here. The result panel will compute total K delivery (KPhos + KCl) and warn if it exceeds the 0.5 mEq/kg/hr ceiling. Default 0 for patients not on KCl.

Awaiting input

Enter a patient weight to see the result.

Reference

How the calculation works

The sliding scale gives a rate in mmol/kg/hr. KPhos stock provides 3 mmol P + 4.4 mEq K per mL. Pump rate and K delivery:

$$\text{mL/hr} = \frac{\text{rate}_{\text{mmol/kg/hr}} \times \text{weight}_{\text{kg}}}{3\,\text{mmol/mL}}$$

$$\text{K from KPhos (mEq/kg/hr)} = \frac{\text{mL/hr} \times 4.4\,\text{mEq/mL}}{\text{weight}_{\text{kg}}}$$

Worked example with current inputs

Enter a patient weight to see the worked example.

Reference

Hypophosphatemia sliding scale

Serum P (mg/dL)	Severity	KPhos rate
P > 2.0 mg/dL	normophosphatemia	not indicated
P 1.5–2.0 mg/dL	mild	0.03 mmol/kg/hr
P 1.0–1.5 mg/dL	moderate	0.06 mmol/kg/hr
P 0.5–1.0 mg/dL	severe	0.09 mmol/kg/hr
P < 0.5 mg/dL	critical	0.12 mmol/kg/hr

Sources

Sliding scale and dosing range: Hoehne SN. Diabetic Ketoacidosis. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 3rd ed. Elsevier; 2023. Chapter 73, Box 73.1 (KPhos rate range 0.03–0.12 mmol/kg/hr IV).
Phosphorus disorders overview: DiBartola SP. Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 4th ed. Elsevier; 2012. Chapter 7 (Disorders of Phosphorus).
KPhos preparation: Standard veterinary stock, potassium phosphate injection, USP, provides ≈4.4 mEq K + 3 mmol P per mL. Verify your hospital stock matches before infusing.