The anesthesiologist's response to a low-output state after cardiopulmonary bypass: etiologies and remedies.

Artifacts or mechanical problems may cause data which suggest poor myocardial performance during emergence from cardiopulmonary bypass (CPB). Transducer and monitoring equipment malfunctions, damping of the arterial blood pressure tracing, effects of drugs, hypercarbia, inordinately high intrathoracic pressure, cardiac tamponade, and others are all possible culprits. It is important to have a systematic plan for evaluating and interpreting the signs and data that are evident. Causes of hypotension after CPB include low hematocrit, hypercarbia, sympathetic inhibition, vasodilator action, anaphylaxis or anaphylactoid reactions, protamine reactions, and impaired myocardial performance. Impaired myocardial performance can be attributable to rate and rhythm disturbances, inadequate ventricular preload, inappropriately elevated right and left ventricular afterload, and decreased myocardial contractility. Common causes of hypoxemia include a malfunctioning ventilator system, pulmonary problems such as atelectasis and shunt, anemia, and inordinately high utilization of oxygen.