Quality and outcomes assessment of intravenous unfractionated heparin anticoagulation in venous thromboembolism

Purpose: Achieving a therapeutic activated partial thromboplastin time (aPTT) within 24 hours of intravenous unfractionated heparin (IV UH) initiation has shown a reduction in recurrence and mortality in venous thromboembolism.  This study evaluated IV UH administered according to an institution-specific thromboembolic nomogram to: 1) assess the percentage of patients achieving a therapeutic aPTT within 24 and 48 hours and 2) evaluate compliance and safety.

Methods: A retrospective analysis of 300 adult patients treated with IV UH for at least 24 hours was conducted.  Data abstracted from the medical record included patient demographics, IV UH dosing information and laboratory data. 

Results: A therapeutic aPTT (≥60 seconds) was achieved in 97.3% and 98.7% of all patients within 24 and 48 hours, respectively.  Use of initial bolus, increasing BMI and/or increasing body weight did not impact the percentage of patients achieving therapeutic aPTT.  Eighty-one percent of patients receiving the nomogram recommended initial bolus had supratherapeutic aPTTs (>85 seconds) upon first draw versus 43% of patients not receiving an initial bolus.  Fifty-one percent of supratherapeutic aPTTs on first draw were above the upper limit of laboratory detection (>180 seconds).  Full compliance to the nomogram was observed in 21% of patients.  Major bleeding occurred in 26.3% of patients.

Conclusion: The institution-specific IV UH nomogram is successful in rapidly achieving a therapeutic aPTT within 24 and 48 hours irrespective of BMI, weight, or bolus administration.  The high rate of supratherapeutic initial aPTTs observed in this study calls into question the appropriateness of the recommended initial bolus, as the majority of patients achieved the primary endpoint regardless of bolus administration. Though observed rates of major bleeding were consistent with previous studies, future studies are needed to characterize the relationship between aPTT and bleeding risk and to further explore heparin dosing options that optimally balance efficacy and safety.