Start with a clinical endpoint
Define what will be assessed: pain score, blood pressure, glucose, urine output, rhythm, electrolyte value or another measurable response. Reassess and titrate to that endpoint.
Constant Rate Infusion Calculator
Four veterinary workflows in one familiar calculator: mixed Multiple protocols, the full Single-drug formulary, a dedicated regular-insulin DKA protocol, and a custom-medication Quick CRI syringe / bag builder. Includes titration tables, reverse lookup, exact final-volume preparation checks and printable pump sheets.
Patient
Start with the patient
Weight units, species and the current measured weight.
Workflow
Choose the workflow
Multiple drugs in one mixture, a single drug, the regular-insulin DKA protocol, or a custom Quick CRI.
Infusion type
Medication and dose
Set the medication and the dose
The drug or combination, its source concentration, and the target dose you want to run.
Drug — [A/B/C] = evidence tier
Dose — current target
mcg/kg/min
lowhigh
Loading dose — adjust to your patient
mcg/kg
lowhigh
Reversal dose
mg/kg
lowhigh
Regular (soluble) insulin U-100 — DKA protocol. The insulin solution is a dedicated pump/line, separate from the patient’s replacement-fluid and dextrose bag. The 250 mL bag factors, 50 mL full-set prime/discard and BG rate table are locked to the published MSD/Merck protocol.
Blood-glucose units: this published table uses mg/dL. If your analyser reports mmol/L, convert first: mg/dL = mmol/L × 18.
Separate dextrose-fluid bagexact final-volume mixing
Potassium safety checkall potassium sources combined
Custom medication syringe / bag builder. Use this when the medication or prescribed dose is not in the curated list. Enter the source product, loading dose if required, CRI dose, selected fluid, final container volume and planned pump rate. The calculator supplies measured syringe or nominal bag-volume arithmetic; compatibility must be verified separately.
Delivery and preparation
Say how it is being given
How the medication reaches the patient decides which preparation figures the result shows.
How is it being given?
Set the dilution by
The concentration is chosen so the whole dose range fits under this pump rate. Titrate up or down all shift without remaking the syringe.
Describe the solution by
Result
The calculated preparation
This updates as you change any value above — there is nothing to submit.
ResultSyringe pump
Enter a weight and dose to calculate.
For use by veterinary professionals. Verify all calculations against your clinic's protocols, current Plumb's / product label, and the patient's clinical status before administration. This tool shows deterministic arithmetic only — it does not make dosing decisions.
How this tool works
About veterinary constant rate infusions
A constant rate infusion (CRI) delivers a medication continuously at a calculated rate. CRIs may provide more consistent exposure than intermittent dosing and allow controlled titration, but “constant” describes the pump rate—not immediate steady state or a guaranteed clinical effect. Steady state generally takes several elimination half-lives unless a protocol-specific loading strategy is prescribed; distribution, altered clearance and patient factors can change the response.
Medication coverage includes analgesic and anaesthetic CRIs such as fentanyl, morphine, methadone, ketamine, lidocaine, dexmedetomidine, propofol and alfaxalone; cardiovascular infusions including norepinephrine, dopamine, dobutamine and nitroprusside; plus insulin, furosemide, metoclopramide, calcium, magnesium, potassium and phosphate protocols.
Treat the carrier as fluid
Medication fluid, line flushes, nutrition and all other inputs belong in the fluid plan. This is especially important in cats, small dogs and patients at risk of fluid intolerance.
Arithmetic is one safety check
A correct calculation does not confirm the dose, route, diluent, compatibility, stability, container, tubing, access or beyond-use time. Those checks remain essential.
Common components of multimodal analgesic CRIs
Ketamine
At subanaesthetic rates, ketamine is used as an NMDA-receptor antagonist and adjunct within a multimodal acute-pain plan. It should not be presented as complete analgesia or as adverse-effect-free. Monitor pain response, mentation and behaviour, muscle tone, heart rate and blood pressure.
Opioids
A continuous opioid infusion can reduce peak-to-trough variation and can be titrated to response. Morphine, methadone, fentanyl and hydromorphone are full μ-agonists; buprenorphine is a partial μ-agonist, while butorphanol has a different receptor profile and is generally suited to mild pain. These drugs differ in potency, duration and analgesic ceiling and are not clinically interchangeable. Monitor analgesia, sedation, ventilation, temperature, cardiovascular variables and gastrointestinal effects.
Lidocaine
Systemic IV lidocaine is used as a multimodal analgesic adjunct in dogs under a validated protocol. MSD's feline analgesic table lists IV lidocaine CRI as not recommended, while WSAVA advises caution because haemodynamic compromise can occur. This concerns analgesia: feline antiarrhythmic use and local or regional lidocaine are separate indications with different dosing and monitoring. Monitor all systemic use for CNS and cardiovascular toxicity.
Ways to deliver a CRI
Dedicated syringe pump
Useful for small volumes, titratable drugs and high-alert medications. Check the device's minimum accurate rate, syringe compatibility, extension-set dead space, priming and occlusion alarms.
Shared combination syringe or bag
Every component remains in a fixed ratio, so changing the pump rate changes every drug together. Verify the exact products, concentrations, diluent, container and stability. If the protocol prescribes a loading dose, calculate and verify it separately; never create it by accelerating the maintenance mixture.
Medication in a fluid bag
The medication dose is tied directly to the fluid rate. If the patient's fluid prescription changes, the drug dose changes too. Use only when the route, compatibility, stability and required final concentration are validated. Never use a drug-containing maintenance bag for a fluid bolus or resuscitation.
Separate pumps or lines
Separate delivery allows independent drug and fluid titration. If infusions share a catheter, confirm Y-site compatibility and account for connector and tubing dead space to prevent delay or accidental bolus.
Preparation, monitoring and common errors
Before starting
- Confirm patient, species, current measured weight, indication and route.
- Read the order back with the dose unit and time unit in full.
- Distinguish source concentration from final working concentration.
- Verify diluent, container, tubing, filter/light requirements and beyond-use time.
- Label total drug, final concentration, rate, preparation time and expiry.
- Prime safely and obtain an independent calculation and pump check.
During the infusion
- Track the intended clinical endpoint and adverse effects at defined intervals.
- Monitor pain/sedation, respiratory status, heart rate/rhythm, blood pressure and temperature as appropriate.
- Record pump volume infused and include the carrier in total fluid balance.
- Follow drug-specific laboratory monitoring, including glucose, electrolytes, renal or hepatic values when indicated.
- Recalculate and relabel after any dose, concentration, rate or container change.
Frequent traps
- Confusing mg with mcg, minutes with hours, or kilograms with pounds.
- Entering the product percentage as mg/mL without converting it.
- Assuming a commercial bag contains exactly its labelled volume; prepare or measure an exact final volume when concentration must be exact.
- Measuring a source volume below the accuracy of the available syringe.
- Changing a carrier-fluid rate without recalculating the drug dose.
- Loading by accelerating a maintenance infusion or mixed-drug container.
- Using a preparation beyond verified physicochemical stability or aseptic policy.
Core CRI and fluid relationships
Normalize the units first, then keep the amount and time units consistent through every step.
amount / time = dose × weight
mL / time = amount / time ÷ working concentration
delivered dose = concentration × pump rate ÷ weight
container duration = usable volume ÷ pump rate
gtt / min = mL / hr × drop factor ÷ 60
carrier mL / kg / hr = pump mL / hr ÷ weight kg
Duration is a limit, not a permission. Usable duration is the shorter of the calculated container duration and the verified physicochemical stability or aseptic beyond-use time.
Gravity delivery needs close observation. Patient movement and bag height can change the rate, and there are no pump alarms. Gravity delivery may be unsuitable for high-alert or rapidly titrated medications; use an electronic pump when precise delivery is required. A syringe pump may be more accurate for very small volumes, but its limits are device-specific.
Veterinary CRI calculator FAQ
What does CRI stand for in veterinary medicine?
CRI stands for constant rate infusion. It delivers a prescribed medication continuously at a calculated rate, usually through a syringe or infusion pump.
How is a veterinary CRI pump rate calculated?
Convert the prescribed dose to the medication amount required per unit time for the patient's weight, then divide by the final working concentration. Units must remain consistent throughout the calculation.
Can CRI medication be added to an IV fluid bag?
Only when the exact product, diluent, concentration, container and intended duration have been verified as compatible and stable. The medication dose becomes directly tied to the fluid rate, and a medicated maintenance bag must not be used for a fluid bolus or resuscitation.
Does this veterinary CRI calculator choose a safe dose?
No. The calculator performs deterministic arithmetic and physical-fit checks. A veterinary professional must verify the dose, indication, route, preparation, compatibility, stability, monitoring and patient-specific suitability.
Are CRI doses the same for dogs and cats?
No. Dose ranges, adverse-effect risks and accepted uses can differ substantially between dogs and cats. Select the correct species and verify the result against a current veterinary reference and local protocol.
Clinical references: 2022 WSAVA Global Pain Management Guidelines · 2022 AAHA Pain Management Guidelines · MSD Veterinary Manual: Analgesics Used in Animals · Merck Veterinary Manual: Pharmacokinetics · 2024 AAHA Fluid Administration and Monitoring · 2024 AAHA Fluid Overload guidance. Guidance changes over time; use the current formulary, product information and hospital policy for each patient.
An ASK A VET™ clinical tool. Talk. Track. Trust.
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