Applied Pharmacology in Cardiopulmonary Bypass
What you must understand
Applied pharmacology asks you to translate principles into intraoperative decisions. Master the agents used on and around bypass: heparin for anticoagulation, protamine for reversal, antifibrinolytics (tranexamic acid, epsilon-aminocaproic acid), inotropes and vasopressors (epinephrine, norepinephrine, dobutamine, milrinone, vasopressin), vasodilators (nitroprusside, nitroglycerin), and anesthetics/sedatives (propofol, volatile agents, opioids).
Understand the heparin-antithrombin mechanism and why ACT monitoring is used. Know that protamine can cause histamine-mediated hypotension, pulmonary vasoconstriction, and, rarely, catastrophic reactions. Recognize that milrinone is an inodilator cleared renally and can cause hypotension, while vasopressin acts via V1 receptors independent of adrenergic pathways - useful in catecholamine-refractory vasoplegia.
Traps in questions
Questions often test the protamine-to-heparin ratio and the difference between total-dose and titrated reversal. Another trap: assuming volatile anesthetics are inert - they cause dose-dependent vasodilation and myocardial depression. Watch for confusion between inotropes (increase contractility) and vasopressors (increase vascular tone).
Rule of thumb
Match the drug to the physiology: pump problem → inotrope; pipe problem → vasopressor or vasodilator. Worked example: post-bypass vasoplegia with low SVR and adequate cardiac output - choose a vasopressor (norepinephrine or vasopressin), not an inotrope.