Activated Clotting Time during Cardiopulmonary Bypass: Is Repetition Necessary during Open Heart Surgery?

We evaluated the need of activated clotting time monitoring and efficacy of heparinization protocol in 100 patients undergoing open heart surgery. Patients were anticoagulated with 300 or 400 units·kg⁻¹ heparin, based on their heparin sensitivity assessed at 5 min by activated clotting time. One-third of the initial dose was repeated at 90 min and thereafter hourly until completion of cardiopulmonary bypass. Patients who attained an activated clotting time of > 350 seconds at 5 min were included. Activated clotting time was repeated every 30 min. A time of < 350 seconds or presence of clot in the surgical field/extracorporeal circuit was considered failure of the protocol. Cardiopulmonary bypass was performed using a membrane oxygenator, non-pulsatile flow, hypothermia and crystalloid/blood priming solution. At 5 min, 94 patients had activated clotting time of > 350 seconds, 6 were < 350 seconds. At predetermined time intervals of 30 min, up to 210 min, 406 activated clotting time measurements were above 400 seconds and 40 were between 350 and 400 seconds. No clot was observed in the surgical field or extracorporeal circuit. This anticoagulation protocol ensures adequate anticoagulation during hypothermic cardiopulmonary bypass. With this protocol, only one activated clotting time at 5 min after heparin administration is required and essential; subsequent monitoring is not necessary.