Anticoagulant effects of inhaled unfractionated heparin in the dog as determined by partial thromboplastin time and factor Xa activity

OBJECTIVE: To evaluate the anticoagulant effects of inhaled heparin in dogs. DESIGN: This study was conducted in 3 phases. In phase 1, bronchoalveolar lavage fluid (BALf) was collected to generate an in vitro calibration curve to relate heparin concentration to the activated partial thromboplastin time (aPTT). In phase 2, heparin was administered via nebulization to determine the threshold dose needed to prolong systemic aPTT. In phase 3, the local anticoagulant activity of inhaled heparin was determined by measurement of BALf anti‐Xa activity and aPTT. SETTING: University teaching hospital. ANIMALS: Six healthy intact female Walker Hounds were used in this study. Two dogs were used for each phase. INTERVENTIONS: Inhaled unfractionated sodium heparin was administered in doses ranging from 50,000 to 200,000 IU. RESULTS: In vitro addition of heparin to BALf caused a prolongation in aPTT. Inhaled heparin at doses as high as 200,000 IU failed to prolong systemic aPTT, and a threshold dose could not be determined. No significant local anticoagulant effects were detected. CONCLUSIONS: Even at doses higher than those known to be effective in people, inhaled heparin appears to have no detectable local or systemic anticoagulant effects in dogs with the current delivery method.