The Anesthesiologist's Response to a Low-Output State After Cardiopulmonary Bypass: Etiologies and Remedies

Abstract

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.

Effects of chronic angiotensin II receptor antagonist and angiotensin-converting enzyme inhibitor treatments on neurohormonal levels and haemodynamics during cardiopulmonary bypass †

“…Mechanical ventilation was controlled to maintain normocarbia (4.7-5.0 kPa). The depth of anaesthesia was monitored with a bispectral index score (BIS) monitor (A-200 BIS monitor, Aspect Medical System Inc., Newton, MA, USA) and maintained at 50 (5). Any mean arterial pressure (MAP) below 60 mm Hg during the induction of anaesthesia or during surgery, was treated by 100 mg of phenylephrine.…”

“…4 Cardiopulmonary bypass (CPB) frequently causes hypotension as a result of tissue hypoxia and hypoperfusion, haemodilution and systemic inflammatory response. [5][6][7][8] It is usually transient and mild because of subsequent temporary elevation in several vasoconstrictive substances, 9 10 and temporary administration of low dose of vasopressor is usually sufficient to maintain perfusion pressure. However, deleterious vasodilatory shock may develop during CPB, requiring large amounts of vasopressors, which may be associated with difficulty in weaning from CPB and poor prognosis.…”