Enter dosage in micrograms per kilogram per minute.
The concentration of the drug in the vial.
250 mL
500 mL
1000 mL (1L)
3000 mL (3L)
5000 mL (5L)
Volume to Add to Bag:– mL
Total Drug Amount in Bag:– mg
Hourly Drug Delivery:– mg/hr
Final Bag Concentration:– mg/mL
Note: Remove an equivalent volume of fluid from the bag before adding the drug to ensure exact concentration, especially for smaller bag sizes.
function calculateCRI() {
// Get input values
var weight = parseFloat(document.getElementById('dogWeight').value);
var doseMcg = parseFloat(document.getElementById('targetDose').value);
var drugConc = parseFloat(document.getElementById('drugConcentration').value);
var fluidRate = parseFloat(document.getElementById('fluidRate').value);
var bagSize = parseFloat(document.getElementById('bagSize').value);
// Validation
if (isNaN(weight) || isNaN(doseMcg) || isNaN(drugConc) || isNaN(fluidRate) || isNaN(bagSize) ||
weight <= 0 || doseMcg <= 0 || drugConc <= 0 || fluidRate <= 0 || bagSize <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Calculation Logic
// 1. Calculate how many mg per hour the dog needs
// Formula: (Dose in mcg * Weight * 60 mins) / 1000 (to convert mcg to mg)
var mgPerHour = (doseMcg * weight * 60) / 1000;
// 2. Calculate the required concentration in the fluid bag (mg/mL)
// Formula: mg required per hour / fluid rate in mL/hour
var requiredConcMgMl = mgPerHour / fluidRate;
// 3. Calculate total mg needed for the full bag size
// Formula: Required Concentration * Bag Size
var totalMgNeeded = requiredConcMgMl * bagSize;
// 4. Calculate the Volume (mL) of the drug to add to the bag
// Formula: Total mg needed / Drug Concentration (mg/mL)
var volToAdd = totalMgNeeded / drugConc;
// Display Results
document.getElementById('resVolumeToAdd').innerHTML = volToAdd.toFixed(2) + " mL";
document.getElementById('resTotalMg').innerHTML = totalMgNeeded.toFixed(1) + " mg";
document.getElementById('resHourlyMg').innerHTML = mgPerHour.toFixed(2) + " mg/hr";
document.getElementById('resFinalConc').innerHTML = requiredConcMgMl.toFixed(4) + " mg/mL";
// Show result area
document.getElementById('result-area').style.display = 'block';
}
Understanding Constant Rate Infusions (CRI) in Veterinary Medicine
A Constant Rate Infusion (CRI) is a method used in veterinary medicine to deliver drugs continuously over a specific period. This is predominantly used for analgesia (pain management), anesthesia, or fluid therapy management in dogs. By administering medication at a constant rate, veterinarians can maintain steady plasma drug concentrations, avoiding the "peaks and troughs" associated with bolus injections.
How the Calculation Works
Calculating a CRI manually involves several steps to ensure the patient receives the correct dosage based on their weight and the rate of fluid administration. This calculator uses the "Add to Bag" method, which determines how much drug to inject into a fluid bag so that the existing fluid rate delivers the desired dosage.
The core logic follows this sequence:
Step 1: Determine Hourly Requirement. We calculate the total milligrams (mg) of the drug the dog needs per hour based on the target dose (mcg/kg/min) and body weight.
Step 2: Determine Fluid Concentration. Based on the IV fluid rate (mL/hr), we determine how concentrated the fluid needs to be (mg/mL) to deliver that hourly requirement.
Step 3: Calculate Additive Volume. We calculate the total amount of drug required for the specific bag size (e.g., 1000mL) and convert that to milliliters (mL) based on the drug's vial concentration.
Common CRI Drugs for Dogs
Veterinary professionals frequently use CRIs for multimodal pain management. Some common agents include:
Lidocaine: Often used for visceral pain and systemic analgesia. Common dosages range from 25 to 50 mcg/kg/min.
Ketamine: Used at sub-anesthetic doses (micro-doses) to prevent wind-up pain (central sensitization). Common dosages range from 2 to 10 mcg/kg/min.
Fentanyl: A potent opioid for severe pain. Dosages vary significantly based on the patient's status.
MLK (Morphine, Lidocaine, Ketamine): A popular combination for severe pain management requiring complex calculations.
Safety Precautions
Veterinary Disclaimer: This calculator is a support tool for educational and verification purposes only. It does not replace professional veterinary judgment.
Always double-check calculations before administering medication. Factors such as the patient's hydration status, renal function, and concurrent medications must be considered. When adding a significant volume of drug to a fluid bag, it is standard practice to remove an equal volume of fluid first to prevent dilution errors, ensuring the final concentration remains accurate.