Excess Unfractionated Heparin Dosing for STEMI and NSTEMI


In This Article

Site Interview

(1) How was this issue identified?
Starting in quarter 1 2007, we noticed the high rate of excess dosing for heparin on our ACTION site reports compared to national rates.

(2) What did you do to understand the problem?
We use a standard order form for UFH dosing, which was approved by our pharmacy. It is used throughout the hospital for NSTEMI and STEMI patients. It has been in place for a while, so we started there.

Our heparin standing order form calls for an initial dose of 80 U/kg IV bolus and 18 U/kg/min IV infusion (without upper limits), based on the patient's ideal body weight (not actual weight). The weight-based adjustment was based on partial thromboplastin time (PTT) results, and called for:

If PTT is < 32, then give another 80 U/kg bolus and increase infusion by 4/U/kg/h;
If PTT is 32-42, then give another 40 U/kg bolus and increase infusion by 2 U/kg/h;
If PTT is 43-67, then no change;
If PTT is 68-86, then reduce infusion by 2 U/kg; and
If PTT is > 86, stop infusion for 1 hour, then restart with dose reduced by 3 U/kg.

This is the algorithm recommended for venous thrombosis by the Seventh American College of Chest Physicians (ACCP) Conference on Antithrombotic and Thrombolytic Therapy related to the use of Heparin and Low Molecular Weight Heparin1. It was the only heparin order form we had at the time.

(3) What have you done to change your process?
We modified our heparin order form in November 2007 for cardiac patients. We now use the recommended dose based on the ACC/AHA Guidelines for the Management of Patients With Unstable Angina/NSTEMI. In this document, the recommended initial bolus dose is 60-70 U/kg and initial infusion dose is 12-15 U/kg/h. In addition, the guideline update2 has added a bolus cap of 4000 U for NSTEMI (previously a cap only for STEMI) and lowered the initial bolus dose to 60 U/kg and infusion dose to 12 U/kg/h. These guidelines do not specify a weight-based adjustment for subsequent changes based on PTT, so we came up with the following algorithm:

If PTT is < 32, then give a 40 U/kg bolus and increase infusion by 100 U/h;
If PTT is 32-42, then increase rate by 100 U/h;
If PTT is 43-67, then no change;
If PTT is 68-86, then reduce rate by 100 U/h; and
If PTT is > 86, we hold heparin for 1 hour and restart as a reduced dose.

We also stopped using ideal body weight and now use actual weight.

(4) How are things going now at your site?
We realized that the re-agents our lab uses to determine PTT values vary on a yearly basis (when reordered) such that our normal range values also differ on a yearly basis. Our heparin order form had dose adjustment based on PTT ranges. However, a PTT of 32-42 last year is now equivalent to a PTT of 32-52 in terms of its relationship to control. Therapeutic range (1.5-2.0 times control) is now a PTT of 52-92 in our lab. Therefore, we are scaling based on the new control values for our site.