Reevaluation of a weight-based heparin dosing nomogram: is institution-specific modification necessary?

To compare a heparin dosing nomogram using an initial infusion rate of 18 units/kg/h with physician-directed heparin prescribing and with a modified version of the nomogram adjusted for institution-specific data.

During consecutive phases of this cohort study, patients' intravenous heparin therapies were initiated and adjusted by using one of the following three methods: (1) physician-directed dosing, (2) a body weight-based dosing nomogram with an initial infusion rate of 18 units/kg/h, and (3) a body weight-based dosing nomogram with an initial infusion rate determined by the median dose of heparin (in units/kg/h) required to achieve therapeutic activated partial thromboplastin times (aPTTs) during the first two phases. The time required to achieve therapeutic aPTTs as well as the percentage of initial aPTTs in the therapeutic range were compared for the three phases.

The heparin dosing nomogram in which the initial infusion rate was adjusted for our individual institution resulted in a statistically shorter median time until aPTTs were in the therapeutic range than did either the physician-directed dosing or unmodified nomogram groups (6.1 h in the modified nomogram group, 10.5 h in the physician-directed group, 21.5 h in the unmodified nomogram group; p < 0.05 for all differences). Use of the institution-specific nomogram resulted in the greatest percentage of initial aPTTs in the therapeutic range (84% in the 13 units/kg/h nomogram group vs. 47% in the physician-directed group and 18% in the 18 units/kg/h nomogram group; p < 0.05 for all differences).

Use of a heparin dosing nomogram with an initial infusion rate of 18 units/kg/h resulted in prolongation of the time to reach therapeutic aPTTs. By modifying the nomogram for use at an individual institution, we reduced the time to achieve therapeutic range of aPTTs while still reducing the likelihood of excessive anticoagulation of patients.