Remifentanil Infusion Rate Calculation

Calculated Infusion Rate

0.00 mL/hr

Understanding Remifentanil Infusion Calculations

Remifentanil is a potent, ultra-short-acting synthetic opioid analgesic used frequently in anesthesia for induction and maintenance of general anesthesia, as well as for sedation in critical care settings. Because of its rapid metabolism by non-specific plasma esterases, precise dosing is critical for maintaining a steady state and ensuring rapid recovery.

The Infusion Formula

To calculate the infusion rate in mL/hr from a dose prescribed in mcg/kg/min, the following formula is applied:

Rate (mL/hr) = [Dose (mcg/kg/min) × Weight (kg) × 60 (min/hr)] / Concentration (mcg/mL)

Concentration Calculation

Before finding the mL/hr, you must determine the concentration of the drug in the bag or syringe:

• Concentration (mcg/mL) = [Total mg × 1000] / Total Volume in mL.
• For example, 2 mg of remifentanil in 40 mL results in a concentration of 50 mcg/mL (2000 mcg / 40 mL).

Practical Example

Suppose you have a 80 kg patient and you wish to start an infusion at 0.1 mcg/kg/min. You have prepared a syringe containing 5 mg of Remifentanil in 50 mL of saline (100 mcg/mL).

1. Step 1: Calculate mcg per minute for the patient: 0.1 mcg/kg/min × 80 kg = 8 mcg/min.
2. Step 2: Convert to mcg per hour: 8 mcg/min × 60 min = 480 mcg/hr.
3. Step 3: Divide by concentration: 480 mcg/hr / 100 mcg/mL = 4.8 mL/hr.

Dosing Considerations

Clinical Goal	Typical Dose Range
MAC/Sedation	0.025 – 0.1 mcg/kg/min
General Anesthesia (Maintenance)	0.05 – 0.5 mcg/kg/min
Postoperative Analgesia	0.025 – 0.1 mcg/kg/min

Warning: Remifentanil is a highly potent opioid. Miscalculation can lead to severe respiratory depression or chest wall rigidity. Always verify calculations with a second provider and follow institutional protocols for high-alert medications.

function calculateRemiRate() {
var weight = parseFloat(document.getElementById(‘weight’).value);
var dose = parseFloat(document.getElementById(‘dose’).value);
var mg = parseFloat(document.getElementById(‘rem_mg’).value);
var ml = parseFloat(document.getElementById(‘rem_vol’).value);
var resultBox = document.getElementById(‘remi_result_box’);
var rateOutput = document.getElementById(‘remi_rate_output’);
var summaryOutput = document.getElementById(‘remi_summary’);
if (isNaN(weight) || isNaN(dose) || isNaN(mg) || isNaN(ml) || weight <= 0 || dose < 0 || mg <= 0 || ml <= 0) {
alert("Please enter valid positive numbers for all fields.");
resultBox.style.display = "none";
return;
}
// Calculate Concentration in mcg/mL
var totalMcg = mg * 1000;
var concentration = totalMcg / ml;
// Calculate Rate in mL/hr
// mL/hr = (mcg/kg/min * kg * 60) / concentration
var hourlyMcg = dose * weight * 60;
var mlPerHour = hourlyMcg / concentration;
rateOutput.innerText = mlPerHour.toFixed(2) + " mL/hr";
summaryOutput.innerText = "For a " + weight + " kg patient at " + dose + " mcg/kg/min with a " + concentration.toFixed(1) + " mcg/mL concentration.";
resultBox.style.display = "block";
}