About This Guide

The Heparin Bolus + Infusion Calculator helps clinicians determine the initial weight-based dosing for unfractionated heparin (UFH). This guide provides supplementary information on the tool's outputs, usage, underlying dosing principles, and safety considerations. It is intended for educational purposes and should not replace clinical judgment or institutional protocols.

Understanding the Outputs

The calculator provides four key values required for initiating a heparin infusion:

• Total Bolus Dose (units): The initial one-time dose administered to rapidly achieve a therapeutic level of anticoagulation. The dose is calculated based on weight and the selected indication, subject to a maximum cap.
• Volume for Bolus (mL): The volume of heparin solution to draw up for the bolus dose, based on the concentration of the heparin preparation available.
• Initial Infusion Rate (units/hour): The starting rate of the continuous intravenous infusion, specified in units per hour. This is also weight-based and may be capped.
• Initial Pump Rate (mL/hour): The rate at which the intravenous pump should be set to deliver the desired infusion rate, calculated from the heparin bag concentration.

How to Use the Calculator

To ensure accurate dose calculation, follow these steps:

1. Enter Patient Weight: Input the patient's actual body weight and select the appropriate unit (kg or lbs). Dosing is based on actual weight unless institutional policy dictates otherwise (e.g., for obesity).
2. Select Clinical Indication: Choose the appropriate protocol based on the patient's diagnosis (e.g., VTE, ACS). Different indications use different dosing nomograms, including different bolus multipliers and infusion rates.
3. Define Heparin Bag Concentration: Enter the total units of heparin and the total volume of the IV bag (e.g., 25,000 units in 250 mL). This is critical for calculating the correct volume for the bolus and the final pump rate.

Heparin Dosing Overview

Weight-based heparin dosing aims to provide more reliable and rapid anticoagulation compared to fixed-dose regimens. Protocols are standardized based on the clinical indication, reflecting varying targets for anticoagulation intensity.

• Venous Thromboembolism (VTE) / Atrial Fibrillation: Typically requires a more aggressive initial dose, such as an 80 units/kg bolus followed by an 18 units/kg/hr infusion.
• Acute Coronary Syndrome (ACS) / STEMI: Often uses a more moderate dose, such as a 60 units/kg bolus (with a lower cap) followed by a 12 units/kg/hr infusion.
• Percutaneous Coronary Intervention (PCI): May involve a bolus-only strategy without a subsequent infusion, with dosing adjusted based on activated clotting time (ACT) measurements during the procedure.

Dose capping is a common safety feature in protocols to avoid excessive anticoagulation and bleeding risk in patients with high body weight.

Switching Anticoagulants

Transitioning to or from heparin requires careful timing to balance the risk of thrombosis and bleeding.

• From a DOAC (e.g., apixaban, rivaroxaban) to Heparin: A heparin infusion can typically be started when the next dose of the DOAC would have been due.
• From Warfarin to Heparin: Discontinue warfarin and initiate the heparin infusion once the INR is below the therapeutic range (e.g., <2.0).
• From Heparin to Warfarin: Begin warfarin therapy concurrently with the heparin infusion. The heparin infusion should be continued for at least 5 days and until the INR has been in the therapeutic range for at least 24 hours.

Always consult institutional guidelines for specific switching protocols.

Monitoring and Titration

The initial calculated dose is only a starting point. A continuous heparin infusion requires frequent laboratory monitoring to ensure efficacy and safety. The most common test is the activated partial thromboplastin time (aPTT). The first aPTT is typically drawn 6 hours after the infusion begins, and the rate is adjusted based on a sliding-scale nomogram to maintain the aPTT within the institution's therapeutic range (often 1.5-2.5 times the control value).

Safety Alerts

Heparin is a high-alert medication with significant risks if not managed carefully.

• Bleeding: This is the most common and serious side effect. Patients should be monitored closely for signs of bleeding.
• Heparin-Induced Thrombocytopenia (HIT): A rare but severe immune reaction causing a drop in platelet count and a high risk of thrombosis. Platelet counts must be monitored regularly during therapy.
• Calculation Errors: Dosing errors are a major source of adverse events. All calculations should be independently double-checked by a second clinician before administration.

Frequently Asked Questions

References

1. Stevens SM, Woller SC, Kreuziger LB, et al. Antithrombotic Therapy for VTE Disease: Second Update of the CHEST Guideline and Expert Panel Report. Chest. 2021;160(6):e545-e608. doi:10.1016/j.chest.2021.07.055
2. Levine GN, Bates ER, Bittl JA, et al. 2016 ACC/AHA Guideline Focused Update on Duration of Dual Antiplatelet Therapy in Patients With Coronary Artery Disease. J Am Coll Cardiol. 2016;68(10):1082-1115. doi:10.1016/j.jacc.2016.03.513
3. U.S. Food and Drug Administration. Heparin Sodium Injection Prescribing Information. Drugs@FDA Database. Accessed October 2023. View Sample Label
4. Institute for Safe Medication Practices (ISMP). ISMP Guidelines for Standard Order Sets. ISMP; 2017. www.ismp.org