Falsely increased bispectral index score during deep hypothermic circulatory arrest in cardiac surgery

Abstract

The bispectral index score (BIS) is widely used as an accurate measure of the hypnotic effect of anesthetics and sedative drugs [1]. However, some clinical situations can lead to inaccuracy in its results [2]. We report two cases in which the BIS value constantly exceeded the expected levels during deep hypothermic circulatory arrest (DHCA) in cardiac surgery. A 60-year-old male patient was diagnosed with a type III chronic aortic dissection accompanied by a thoracic aortic aneurysm and severe aortic valve regurgitation (AR). He was scheduled to undergo replacement of the descending thoracic aorta. He underwent Bentall surgery 1 year ago; however, this was complicated by third-degree atrioventricular block with an escape rate of less than 40 beats per minute. Therefore, he had a pacemaker implanted set in the DDD mode (Dual chamber pacing, Dual chamber sensing, Dual chamber function mode). The pacemaker mode was transformed to the DOO mode (Dual chamber pacing, No sensing, No function) before the induction because a fixed rate pacing mode such as the DOO mode can reduce the effect of electromagnetic interference. Anesthesia was induced with 14 mg etomidate, 50 mg rocuro nium, and continuous infusion of remifentanil and propofol. Intra-arterial catheters were inserted, and intubation was performed. We reduced the continuous infusion of rocuronium to 2 μg/kg/min for adequate motor evoked potential (MEP) monitoring. A Swan-Ganz central venous catheter was placed in the left subclavian vein. Another central venous catheter was placed in the left internal jugular vein. Cerebrospinal fluid drainage was also performed at L3-4. Before aortic cross clamping, the patient was cooled to a body temperature of 16.3 o