In clinical settings, heparin is a high-alert medication used for anticoagulation. Calculating the drip rate correctly is vital for patient safety and achieving therapeutic activated partial thromboplastin time (aPTT) levels.
The Mathematical Formula
The standard calculation for an IV infusion rate in mL/hr involves two main steps:
Determine Total Units per Hour: If weight-based, multiply the dose (units/kg/hr) by the patient's weight in kilograms.
Calculate mL/hr: Divide the total units per hour by the concentration (units per mL).
Formula: Rate (mL/hr) = [Dose (units/hr) × Bag Volume (mL)] / Total Units in Bag
Example Calculation
A physician orders a heparin drip at 18 units/kg/hr for a patient weighing 80 kg. The pharmacy provides a bag containing 25,000 units of Heparin in 250 mL of D5W.
Step 1: 18 units × 80 kg = 1,440 units/hr
Step 2: Concentration = 25,000 units / 250 mL = 100 units/mL
Heparin concentrations are standardized in many facilities (e.g., 100 units/mL), but always verify the label on the IV bag. Most hospitals require a second nurse to double-check heparin calculations and pump settings due to the high risk of hemorrhage associated with dosing errors.
function toggleWeightField() {
var method = document.getElementById("dosingMethod").value;
var weightContainer = document.getElementById("weightContainer");
var doseLabel = document.getElementById("doseLabel");
if (method === "fixed") {
weightContainer.style.display = "none";
doseLabel.innerHTML = "Ordered Dose (units/hr)";
} else {
weightContainer.style.display = "block";
doseLabel.innerHTML = "Ordered Dose (units/kg/hr)";
}
}
function calculateHeparinRate() {
var method = document.getElementById("dosingMethod").value;
var weight = parseFloat(document.getElementById("patientWeight").value);
var dose = parseFloat(document.getElementById("orderedDose").value);
var totalUnits = parseFloat(document.getElementById("totalUnits").value);
var bagVolume = parseFloat(document.getElementById("bagVolume").value);
var resultDiv = document.getElementById("heparinResult");
var rateOutput = document.getElementById("rateOutput");
var doseDetail = document.getElementById("doseDetail");
// Validation
if (isNaN(dose) || isNaN(totalUnits) || isNaN(bagVolume) || dose <= 0 || totalUnits <= 0 || bagVolume <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
if (method === "weight" && (isNaN(weight) || weight <= 0)) {
alert("Please enter a valid patient weight.");
return;
}
var unitsPerHour;
if (method === "weight") {
unitsPerHour = dose * weight;
} else {
unitsPerHour = dose;
}
// Rate Calculation: (Units/hr * mL) / Total Units
var mlPerHour = (unitsPerHour * bagVolume) / totalUnits;
// UI Updates
resultDiv.style.display = "block";
rateOutput.innerHTML = mlPerHour.toFixed(1) + " mL/hr";
var detailText = "Total Delivery: " + unitsPerHour.toLocaleString() + " units per hour";
if (method === "weight") {
detailText += " based on " + weight + " kg body weight.";
} else {
detailText += " (Fixed Rate).";
}
doseDetail.innerHTML = detailText;
// Smooth scroll to result
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}