Continuous Rate Infusion Calculator

Calculate drug volumes for constant rate infusions added to fluid bags.

kg

mcg/kg/min mcg/kg/hr mg/kg/min mg/kg/hr

mg/mL

mL/hr

mL

About Continuous Rate Infusion (CRI)

Continuous Rate Infusion (CRI) is a medical and veterinary technique used to administer medication at a constant, controlled rate over a specific period. This is typically achieved by adding a specific volume of a drug to a bag of intravenous fluids, which is then delivered via an infusion pump or gravity drip.

Why use a CRI?

CRIs are preferred for drugs with short half-lives (like Lidocaine, Fentanyl, or Ketamine) where maintaining a steady plasma concentration is crucial for efficacy and safety. Unlike bolus injections, which cause peaks and troughs in drug levels, a CRI provides smooth, continuous therapeutic coverage.

How this Calculator Works

This calculator determines the volume of drug (in mL) required to be added to a specific size fluid bag to achieve a desired dose rate based on the patient's weight and the fluid administration rate.

The Math Behind the Calculation

The standard formula used in this calculator involves finding the total amount of drug needed for the duration the fluid bag will last.

Step 1: Calculate Total Dose per Hour
Depending on your dose units, the calculator converts the requirement to mg/hr. For example, if the dose is in mcg/kg/min:
Rate (mg/hr) = (Dose × Weight × 60) / 1000

Step 2: Calculate Duration of Fluid Bag
Hours = Bag Size (mL) / Fluid Rate (mL/hr)

Step 3: Calculate Total Drug Required
Total mg = Rate (mg/hr) × Hours

Step 4: Calculate Volume to Add
Volume (mL) = Total mg / Drug Concentration (mg/mL)

Common CRI Drugs

• Lidocaine: Often used for analgesia and anti-arrhythmic effects. Typical doses range from 10-50 mcg/kg/min.
• Ketamine: Used for analgesia (MLK drips) to prevent wind-up pain. Typical doses range from 0.1-0.6 mg/kg/hr (approx 2-10 mcg/kg/min).
• Fentanyl: A potent opioid for pain management. Typical doses range from 2-10 mcg/kg/hr.

Safety Precaution

Dilution Warning: When adding a large volume of drug to a fluid bag, it is best practice to withdraw an equivalent volume of fluid from the bag first to maintain the exact concentration calculated. However, for small volumes (e.g., less than 5% of bag volume), this step is sometimes omitted in clinical settings depending on the precision required.

Disclaimer: This calculator is a tool for medical and veterinary professionals. Always verify calculations manually before administering medication.

Summary of Calculation:

Hourly Drug Requirement:

Bag Duration:

Total Drug in Bag:

Note: The volume to add is >10% of the bag size. You should remove " + volumeToAdd.toFixed(1) + " mL of fluid from the bag before adding the drug to ensure accurate concentration.