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.

In step 1 Nurse Collete must determine the unit of measurement that she will calculate.

In this case, she must determine milliliters per hour. Therefore, the answer to our calculation, or "X" in the equation, will be in milliliters per hour.

Next, Nurse Collete identifies the vehicle of the dose available.

This is 500 milliliters since 0.45% sodium chloride is the form the heparin comes in and 500 mL is the amount.

In step 3, Nurse Collete determines the dose that she has, or is available, which is 25,000 units.

Now, Nurse Collete will identify the desired dose to be administered.

This is 18 units per kilogram per hour since this is the ordered dose.

Next, she factors in the patient's weight which is 76 kilograms.

Now Nurse Collete must decide if she should convert the units of measurement. And in this calculation a conversion is not needed because all the units in the equation already match the units available.

Now that Nurse Collete has identified all the parts, it is time for her to set up the equation and solve for X.

First, she takes the equation, which is "X" equals vehicle over have times desired times weight in kilograms.

Then she enters in the values she has identified so "X" equals 500 milliliters over 25,000 units times 18 units per kilogram per hour times 76 kilograms.

She puts 18 units per kilogram per hour times 76 kilograms in the numerator of the equations.

When multiplying the values in the numerator together and eliminating duplicate units of measurement, she gets "X" equals 684,000 milliliters divided by 25,000 hours.

Once completing the last calculation, Nurse Collete gets a final result of "X" equals 27 point 3 6 milliliters per hour.

Now, Nurse Collete evaluates her answer to see if rounding is necessary and determines yes. Nurse Collete's infusion pump is calibrated by tenths so she rounds to the nearest tenth which is 27.4 mL/hr.

Lastly, Nurse Collette reevaluates the medication order and her calculations to ensure that the answer makes sense.

Since the ordered dose is 18 units per kilogram per hour, the patient weighs 76 kilograms and there are 25,000 units of heparin in 500 milliliters, it makes sense to administer the heparin at a rate of 27 point 4 milliliters per hour.

After verifying her calculation with another nurse, Nurse Colette starts the infusion. She will monitor her patient, draw an aPTT in 6 hours, and reevaluate the rate based upon those aPTT results.

Alright, as a quick recap... Anticoagulants are medications that work by interfering with clotting factors in the coagulation cascade, and are used to prevent the formation of thrombi, or blood clots, and to prevent or treat thromboembolic events. Heparin is a high alert medication, and the main side effect is bleeding. If a patient is prescribed an IV heparin infusion, you may need to follow a weight-based protocol. To do that using the dimensional analysis method, set up your formula as "X" equals vehicle over have times desired times weight in kilograms, enter the appropriate values, and solve for "X". Before starting the infusion, recheck your calculations and then verify the result with another nurse.