Time-related effects of heparin sulfate on regional and systemic anticoagulation.

Optimal timing of vascular clamping to anticoagulation during cardiovascular surgical procedures is poorly defined. This study uses a canine model to determine the effectiveness of three different methods of heparin administration. Heparin sulfate (150 IU/kg) was administered by: injection into the jugular vein 5 minutes before infrarenal aortic clamping (Group 1), injection into the terminal aorta immediately after infrarenal aortic clamping (Group 2), and injection into the jugular vein immediately after infrarenal aortic clamping (Group 3). Thrombin clotting times and partial thromboplastin times were measured in venous blood from the upper and lower extremities before (baseline) heparin administration, and 1, 3, and 5 minutes following heparin administration. Activated clotting times were assessed in lower extremity blood at baseline, and at 1 and 5 minutes after heparin injection. Significant differences existed between groups in both upper and lower extremities. Systemic anticoagulation occurred within 1 minute after intravenous heparin administration in Groups 1 and 2 in the lower extremity, and Groups 1 and 3 in the upper extremity. Delayed anticoagulation in the lower extremity was noted with systemic injection after aortic clamping in Group 3, and after regional intra-aortic administration in the upper extremity of Group 2 subjects. Complete anticoagulation was noted by 5 minutes in all groups in both the upper and lower extremities. These results suggest that the safe time period between heparin administration and vascular clamping varies with the route and the timing of its administration. Intravenous administration prior to aortic cross-clamping provided adequate anticoagulation in this canine model in both the upper and lower extremity blood after 1 minute of heparin circulation.(ABSTRACT TRUNCATED AT 250 WORDS)