Cardiopulmonary Bypass, Circulatory Support, and Mechanical Assist Devices
CPB fundamentals
Cardiopulmonary bypass replaces gas exchange and circulation with a venous reservoir, pump, oxygenator, heat exchanger, and arterial filter. Maintain adequate flow indexed to body surface area, mean arterial pressure, and oxygen delivery; flow and pressure are not interchangeable. Anticoagulation with heparin is monitored by activated clotting time, but ACT is a global test affected by hypothermia, hemodilution, and platelet function. Cardioplegia arrests the heart and protects myocardium through diastolic arrest, hypothermia, and substrate supply. Manage acid-base strategy deliberately; alpha-stat preserves autoregulation, while pH-stat increases cerebral blood flow and is often used in some pediatric cases.
Support devices
IABP augments diastolic coronary perfusion and reduces afterload; it is contraindicated in significant aortic regurgitation and aortic dissection. Impella and other percutaneous VADs unload the LV; ECMO supports oxygenation and circulation, but peripheral VA-ECMO can cause differential hypoxia and LV distension. Durable LVADs are preload-dependent and afterload-sensitive; avoid hypovolemia and uncontrolled hypertension. Know device alarms and the meaning of suction events.
Traps
A classic trap is assuming a therapeutic ACT guarantees adequate heparin effect in a patient with antithrombin deficiency or heparin resistance. Another is missing protamine reaction, which can present as hypotension, pulmonary hypertension, or bronchospasm. Do not treat vasoplegia with volume alone; vasopressin and norepinephrine are common. Worked example: after protamine, hypotension with rising PA pressure and bronchospasm suggests protamine reaction; stop protamine, support with vasopressors, and consider reintroduction only with a clear plan. Rule of thumb: on CPB, oxygen delivery and end-organ perfusion matter more than a single pressure number.