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In unfractionated heparin dosing, the combination of patient age and estimated plasma volume predicts initial
1Medical Education Department, Abbott Northwestern Hospital, Minneapolis, Minnesota 55407, USA.
Study Objective:
To determine whether patient factors other than body weight would better predict patients' initial antifactor Xa heparin activity (HA) after start of unfractionated heparin (UFH) therapy.
Design:
Case series.
Setting:
A 625-bed, adults-only, private, tertiary care teaching hospital.
Patients:
Ninety-two patients requiring UFH therapy.
Interventions:
Patients received initial UFH bolus doses of 72-80 U/kg ideal weight and initial UFH infusions of 19.1-21.2 U/kg ideal weight.
Measurements And Main Results:
Fifty-five percent of the first 6-hour HA measurements were supratherapeutic (> 0.7 U/ml antifactor Xa activity). Patient weight was inferior to a combination of age and estimated plasma volume in predicting initial HA. A predictive model including these two factors accounted for 38.5% of variation in first HA levels compared with 17.7% with actual weight alone.
Conclusion:
Weight-based UFH dosing may frequently result in nontherapeutic initial HA levels. Initial UFH dosing might be improved if protocols based on patient age and estimated plasma volume were developed.
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