Heparin Calculations

After reviewing this chapter, you should be able to:

1. State the importance of calculating heparin dosages accurately

2. Calculate heparin dosages being administered intravenously (mL per hr, units per hr)

3. Calculate subcutaneous dosages of heparin

4. Calculate safe heparin dosages based on weight

HEPARIN ERRORS

Heparin has taken center stage in the media. Numerous errors have been reported relating to heparin and have attracted the attention of the health care society and the general public. Heparin is classified as a high-alert medication because it carries a significant risk of causing serious injuries or death to patients if misused. Attention has been given to unfractionated heparin, low-molecular-weight heparin, and warfarin. Cohen (2007), in the text Medication Errors, discusses some of the causes of error with heparin:

• Mix-ups with concentrations of heparin

• Temporary increases in heparin pump rates to give a bolus; error caused by staff forgetting to reset the pump after delivering the bolus

• Tenfold overdoses from using the abbreviation “U” for units

• Various concentrations of IV heparin bags and heparin vials being mixed up, in part because of look-alike vials and bags

These are just a few reasons for errors that have occurred with heparin. The U.S. Pharmacopoeia listed heparin as one of the top 10 medications most frequently involved in medication errors.

Because of the frequency of errors that have occurred with anticoagulants, they have received the focus of attention from ISMP (Institute for Safe Medication Practices) and The Joint Commission. The anticoagulants are among the medications that will receive targeted attention during the coming year from The Joint Commission.

The Joint Commission proposed a 2008 National Patient Safety Goal (NPSG) associated with anticoagulation therapy. The goal is to reduce the likelihood of patient harm associated with this form of therapy. The requirements will apply to all organizations that provide anticoagulation therapy. The implementation expectations began January 1, 2009. These requirements can be viewed on The Joint Commission’s web site at www.jointcommission.org.

Heparin is a potent anticoagulant that prevents clot formation and blood coagulation. Heparin dosages are expressed in (USP) units. The therapeutic range for heparin is determined individually by monitoring the client’s blood clotting value (activated partial thromboplastin time [APTT] measured in seconds). Heparin is considered to be most therapeutically effective when based on weight in kilograms. Heparin infusions are individualized based on the client’s weight. This concept will be discussed later in the chapter. Heparin can be administered intravenously or subcutaneously; it is never administered intramuscularly because of the danger of hematomas (collections of extravasated blood trapped in tissues of skin or in an organ). When administered intravenously, heparin is ordered in units/hr or mL/hr. Usually, however, heparin is ordered on the basis of the units/hr when ordered intravenously and should be administered by an electronic infusion device. Heparin is available in single-dose and multidose vials, as well as in commercially prepared IV solutions. Heparin sodium for injection is available in several strengths (e.g., 100 units per mL; 5,000 units per mL; 20,000 units per mL). Heparin lock fluid solution, which is used for flushing, is available in 10 and 100 units per mL.

CAUTION

It is extremely important that the nurse be aware that heparin sodium for injection and heparin lock solution can never be used interchangeably.

Heparin used for a flush is usually concentrated to 10 units per mL or 100 units per mL. This is a different concentration of heparin than what is administered subcutaneously or intravenously.

Figure 23-1 shows the various heparin dosage strengths. The client requires continuous monitoring while receiving heparin because of the risk for hemorrhage or clots with an incorrect dosage.