Development of a weight-based heparin dosing nomogram in trauma patients (TP)

Introduction: By producing a desired partial thromboplastin time (PTT) within 6 hrs, heparin nomograms have decreased the acuity of the embolic event, and improved outcomes from pulmonary embolus (PE) and deep venous thrombosis (DVT). The Raschke nomogram (80 units(u)kg bolus and 18 u/kg/br infusion), and other published nomograms, may be inappropriate in TP due to comorbidities or heparin resistance that results in over- or under-dosing. The aim of this study was to develop a weight-based heparin dosing nomogram for TP to achieve a therapeutic threshold within 6 hours of initiating therapy. Methods: A retrospective chart review of 50 TP who received heparin for at least 24 hrs for documented DVT and/or PE was performed. Patient demographics and laboratory data were recorded. All heparin doses and follow-up PTTs were recorded and evaluated. Heparin doses were converted to units/kilogram (kilogram body weight used was ideal body weight or adjusted for obesity). The primary outcome measurement was time at which therapeutic PTT was achieved and the dose required to attain this PTT. (Results are mean ± standard deviation.) Results: Time to first exceed therapeutic threshold was 16.5±16.3 hours (hrs) and time to goal therapeutic range was 25±24.3 hrs. At 6 hours, 58% had not surpassed the therapeutic threshold; 46% were subtherapeutic at 24 hrs. Major bleeding occurred in 6 (12%) patients (PTT range 35-114 seconds). Heparin resistance (greater than 40,000 u/d) occurred in 17 (33%) patients. Analysis indicated that a loading dose of 90 u/kg and an initial maintenance dose of 20 u/kg/hr (95% CI 19.9±1.5) would be appropriate. A nomogram for subsequent dosing was developed based on observed data. Conclusions: Dosing of heparin was inadequate. The incidence of bleeding was found to be within the reported rate of 5-20%. The higher initial dosage requirements may be due to the large number of patients with heparin resistance. Prospective validation of the above nomogram is in progress.