Protamine Test Dose: Impact on Activated Clotting Time and Circuit Integrity

Abstract

Background: Recurrent observation of clot in the cardiopulmonary bypass circuit after the administration of a protamine test dose (PTD) prompted concern over the effects of PTDs on patient activated clotting times (ACTs).

Methods: Data were prospectively collected on 120 patients who had cardiopulmonary bypass while undergoing a variety of cardiac surgical procedures from July to October 2018 at the Toronto General Hospital, Toronto, Canada. ACTs were documented before cardiopulmonary bypass termination, after PTDs, and after protamine full doses. Statistical analysis was completed using a paired t test.

Results: The average PTD was calculated to be 36 ± 21 mg or 11% ± 7% of the full protamine dose of 367 ± 153 mg. This "test" dose ranged from 1% to 67% of full dose depending on the anesthetist. Post-PTD ACTs were widely variable. On average, there was a 40% ± 25% drop from the last ACT during cardiopulmonary bypass (650 ± 155 seconds) to the ACT after PTD (376 ± 153 seconds) (P < .0001). In fact, 81% ± 5% of the patients' post-PTD ACTs were lower than the institutional ACT standard of 480 seconds for safe cardiopulmonary bypass initiation.

Conclusions: Regardless of the PTD, there is no reliable way to predict how a patient's ACT will respond to a PTD. Clot formation is possible and circuit integrity is at risk when pump suction devices are continuously in use during PTD administration. Therefore, the study investigators strongly recommend that the direct recovery of mediastinal shed blood into the pump circuit be discontinued before any amount of protamine is administered to the patient.