Monitoring Response Of Disease To Heparin Therapy With The Activated Coagulation Time (ACT)

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Abstract
Believing that treatment of thromboembolic disease with heparin is treatment of a dangerous group of disorders with a potentially dangerous drug, and that sensitivity to heparin varies greatly, one patient to the next, we attempted to model heparin infusion rates to the specific needs of the patient. We gave initial doses proportionate to body weight, and monitored responses by the ACT. We chose this test because it is a precise bedside procedure which reliably reflects the variable responses of patients.Our protocol: (1) Screen for conditions causing a high risk of bleeding on heparin; (2) Infuse an initial i.v. heparin bolus of about 50 units per kilogram of body weight; (3) Follow with pump-controlled i.v. infusion of 15 to 25 units/kilo/hr.; (4) Subsequently alter the infusion rate as needed to maintain an ACT of 150 to 190 seconds; (5) When the ACT has been established within this range, start appropriate oral doses of warfarin; (6) After 3 days or more, when the prothrombin time is 2 to 2-1/2 times the control, discontinue heparin and maintain patient on oral warfarin.Of 100 patients with proven thromboembolic disease treated at close to this protocol, there were none with progressive thromboembolic disease; 95 patients responded, and were converted to oral warfarin; 5 developed major bleeding necessitating discontinuing heparin. Of these 5, 2 were unrecognized high risk patients who should not have received full dose heparin. The other 3 all had ACT'S well above 190 seconds.Our conclusion: For treatment of patients with deep venous thrombosis and/or pulmonary embolism, this protocol of heparin therapy, if followed carefully is effective and reasonably safe.

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