Heparin Dosing and Administration Protocols

Anticoagulants are medications that work by interfering with the clotting factors in the coagulation cascade. These medications are used to prevent the formation of thrombi, or blood clots, and prevent or treat thromboembolic events, which are conditions that occur when a blood clot obstructs a blood vessel like in deep vein thrombosis, pulmonary embolism, ischemic stroke, transient ischemic attack, coronary artery disease, or myocardial infarction.

They're also used to treat patients with coagulation disorders, like disseminated intravascular coagulation, and patients who underwent cardiac valve replacement or coronary angioplasty; and they are used during procedures like cardiopulmonary bypass, percutaneous coronary intervention, extracorporeal membrane oxygenation, and hemodialysis.

Now, heparin is a commonly used anticoagulant, and it’s a high-alert medication, meaning there’s an increased risk of patient harm if administered in error. This is because heparin can cause unwanted and potentially dangerous bleeding.

Okay now, when administering a heparin IV infusion, you’ll likely follow a weight-based protocol, meaning the dose is based on the patient’s weight, which helps to ensure safe dosing for each patient. Then, the infusion is adjusted, or titrated, based on their activated partial thromboplastin time, or aPTT, results, which measures both the intrinsic and common pathways of the coagulation cascade.

Alright, since heparin is a high-alert medication due to the risk for bleeding, you will always infuse it using an electronic IV infusion pump. It is delivered in milliliters per hour, but because heparin is dosed in units, you need to calculate the heparin infusion rate in units per hour and convert that dosage into milliliters per hour, which is what you program into the infusion pump.

So, to calculate an IV heparin dose, you first need to understand how to calculate a weight-based calculation. Let’s look at the following scenario.

Nurse Colette works on the intermediate medical care unit, and is caring for Reginald, a 76-year-old male who has an acute pulmonary embolism. She reviews Reginald’s electronic health record, or EHR, and sees that his weight from this morning was documented as 76 kilograms.

Nurse Colette notes Reginald’s baseline aPTT is 37 seconds, he received a heparin bolus in the emergency department, and he is ordered an IV heparin infusion. Based on the heparin order, Nurse Collete will calculate the correct rate of infusion and recheck the aPTT 6 hours after the infusion starts.

First, Nurse Colette carefully reads the heparin order which is:

Heparin 25,000 units in 500 milliliters of 0.45 percent sodium chloride premix for continuous intravenous use

The ordered starting rate is 18 units per kilogram per hour

Nurse Collete must determine the rate, in milliliters per hour, to program the infusion pump.

To calculate the answer, Nurse Colette can use one of three calculation methods. Dimensional Analysis; the Basic Formula Method, sometimes called the Desired Over Have Method; or Ratio and Proportion.

When using any of these methods, “X” represents the answer, in this case the rate of infusion, “Vehicle” is the form and amount in which the drug comes like tablets, capsules, or liquid, “Have” is the total dosage strength available, and “Desired” is ordered dose.

The first calculation method is Dimensional Analysis Method, where Nurse Collette will make the total milliliters per hour “X” and set up the formula to solve for “X” like this:

X equals Vehicle over have multiplied by desired multiplied by weight in kilograms

Next, for Basic Formula Method, Collette will make the total milliliters per hour “X” and set up the formula to solve for “X” like this:

X equals desired over have times vehicle times weight in kilograms

Lastly, for the Ratio and Proportion method, Collette will make the total milliliters per hour “X” and set up the formula to solve for “X” like this:

Have over vehicle equals desired times weight in kilograms over X

Now Nurse Collete will work through the steps of the calculation using the dimensional analysis method.