Evaluation of the use of a heparin dose‐response test in dogs to determine the optimal heparin dose during intravascular procedures and assessment of the in vitro heparin response in healthy dogs.

Background: No guidelines for administering and monitoring anticoagulants intraprocedurally are currently available in dogs, despite the prevalence of procedures necessitating systemic anticoagulation with heparin. Objectives: To evaluate an activated clotting time (ACT)‐based heparin dose‐response (HDR) test to predict the individual required heparin dose in dogs during intravascular procedures, and to investigate both the in vitro heparin – ACT and in vitro heparin – factor anti‐Xa activity (anti‐Xa) relationships in dogs. Methods: Blood was collected from eight healthy beagles undergoing a cardiac procedure and utilised to establish baseline ACT and for in vitro evaluation. Subsequently, 100 IU/kg heparin was administered intravenously (IV) and ACT was remeasured (HDR test). The required heparin dose for an ACT target response ≥300 s was calculated for each individual and ACT was remeasured after administration of this dose. For in vitro testing, a serial heparin blood dilution (0‐0.5‐1‐2‐4 international unit (IU)/mL) was prepared and ACT and anti‐Xa were determined using whole blood and frozen plasma, respectively. Results: The HDR test overestimated the required heparin dose in 3/7 dogs. In vitro, ACT and anti‐Xa increased significantly with increasing blood heparin concentration. Heparin – ACT was nonlinear in 4/8 dogs at heparin concentrations >2 IU/mL, whereas heparin – anti‐Xa remained linear throughout the tested range. Conclusions: The HDR test poorly estimated the required heparin dose in dogs. This is most likely attributed to a nonlinear heparin – ACT relationship, as observed in vitro. Anti‐Xa is a promising alternative for ACT; however, unavailability as a point‐of‐care test and lack of in vivo target values restrict its current use. [ABSTRACT FROM AUTHOR]