The bispectral index in relation to ventilation, gas exchange, lactate and acid–base status during pediatric cardiac surgery with cardiopulmonary bypass

Relevance. A decrease in BIS during cardiac surgery is usually interpreted as deepening of anesthesia. However, cortical electrical activity also depends on cerebral perfusion, carbon dioxide tension and metabolic status, which change substantially during cardiopulmonary bypass, when gas exchange is provided by the oxygenator and tissue perfusion depends on pump flow. In children with congenital heart defects, who are prone to hypoxemia and lactic acidosis, a fall in BIS may therefore reflect not only anesthetic effects but also impaired cerebral oxygen supply. Clarifying the contribution of ventilatory, gas-exchange and metabolic variables to BIS is necessary for its correct clinical interpretation.