Which of the following drugs is a serine protease inhibitor administered during CPB to decrease perioperative bleeding?

Aprotinin is a serine protease inhibitor that is used during cardiopulmonary bypass (CPB) to reduce perioperative bleeding. It works by inhibiting various proteolytic enzymes that are involved in the clotting process, particularly fibrinolytic enzymes that break down fibrin clots.

By inhibiting these enzymes, aprotinin helps to stabilize clots and minimize bleeding during and after surgery. This effect is particularly beneficial in complex surgeries, such as cardiac operations, where maintaining hemostasis is critical to positive patient outcomes. The use of aprotinin has been studied extensively and has been shown to reduce the need for transfusions and improve overall recovery times.

In contrast, the other choices listed do not serve as serine protease inhibitors for the purpose of decreasing bleeding in the CPB setting. For example, protamine is primarily used to reverse the effects of heparin, Amicar (aminocaproic acid) is an antifibrinolytic agent but not a serine protease inhibitor, and corticosteroids are used for their anti-inflammatory effects rather than directly influencing bleeding through protease inhibition.