Veterinary CRI (Constant Rate Infusion) Calculator
This tool helps veterinary professionals calculate the correct volume of a drug to add to an IV fluid bag to create a Constant Rate Infusion (CRI) for a patient.
Calculation Results
Enter the values above and click "Calculate" to see the results.
How to Use the CRI Calculator
To accurately determine the drug volume for your CRI, please provide the following information:
- Patient Weight (kg): The animal's body weight in kilograms.
- Desired Drug Dose (mcg/kg/min): The prescribed dose rate in micrograms per kilogram per minute. This is a common unit for CRI drugs like fentanyl, lidocaine, and ketamine.
- Drug Concentration (mg/mL): The concentration of the stock drug solution you are using, found on the vial. For example, 2% lidocaine is 20 mg/mL.
- Fluid Bag Volume (mL): The total volume of the IV fluid bag you are adding the drug to (e.g., 250, 500, 1000 mL).
- IV Fluid Rate (mL/hr): The rate at which the patient will receive the mixed fluids, as set on the IV pump.
Understanding the CRI Calculation Formula
The calculator determines the volume of drug to add by ensuring the patient receives the correct dose at the specified fluid rate. The core formula used is:
Volume to Add (mL) = (Patient Weight * Drug Dose * 60 * Bag Volume) / (1000 * Fluid Rate * Drug Concentration)
Here's a breakdown of the components:
Patient Weight * Drug Dose: Calculates the total micrograms of drug needed per minute.* 60: Converts the per-minute dose to a per-hour dose./ 1000: Converts the dose from micrograms (mcg) to milligrams (mg).- This gives the total mg/hr the patient needs. We then determine the required concentration in the bag and work backward to find the volume of stock solution to add.
Example CRI Calculation
Let's calculate a lidocaine CRI for a 20 kg dog.
- Patient Weight: 20 kg
- Desired Dose: 50 mcg/kg/min
- Drug Concentration: 20 mg/mL (2% lidocaine)
- Fluid Bag Volume: 1000 mL
- IV Fluid Rate: 40 mL/hr (a typical 2x maintenance rate)
Using the formula:
Volume to Add = (20 * 50 * 60 * 1000) / (1000 * 40 * 20)
Volume to Add = 60,000,000 / 800,000
Volume to Add = 75 mL
Therefore, you would add 75 mL of 20 mg/mL lidocaine to the 1000 mL fluid bag.
Important Considerations for CRIs
- Always double-check calculations. This tool is for assistance, but manual verification is crucial for patient safety.
- Label the bag clearly. The IV bag must be clearly labeled with the drug name, total amount added, final concentration, date, time, and patient's name.
- Volume Displacement: For maximum accuracy, especially with large drug volumes, consider first removing a volume of fluid from the bag equal to the volume of drug you will be adding.
- Patient Monitoring: Closely monitor the patient for therapeutic effect and any signs of adverse reactions. Adjust the fluid rate (and thus the drug dose) as directed by the veterinarian.
- Disclaimer: This calculator is an educational tool and should not replace professional veterinary judgment. All medical treatments should be administered under the direction of a licensed veterinarian.
Calculation Results
' + 'Add ' + drugVolumeToAdd.toFixed(2) + ' mL of drug to the fluid bag.' + '' + 'Final Concentration in Bag: ' + finalConcentrationMgPerMl.toFixed(3) + ' mg/mL' + '(or ' + finalConcentrationMcgPerMl.toFixed(2) + ' mcg/mL)' + 'IV Pump Rate: ' + fluidRate.toFixed(1) + ' mL/hr'; resultDiv.innerHTML = resultHTML; }