Changes in Bispectral Index with different positions during general anaesthesia.

Abstract

Background & Objective: Bispectral index (BIS) is used for intraoperative anesthesia depth assessment during general anesthesia (GA). This monitoring modality has been used routinely at many centers during GA, but especially during susceptible patients, in which precise depth of anesthesia is required. We aimed to compare changes of BIS in different head positions under GA, but without surgical stimulation. Methodology: Thirty ASA physical status I patients aged 18−60 y were recruited for this prospective, observational study after ethical approval by the institutional ethical review committee. After administration of GA, patients were kept in supine position for 15 min and the BIS, signal quality index (SQI), electromyography (EMG), mean arterial pressure (MAP) and heart rate (HR) were recorded. Patients were then sequentially placed in: reverse Trendelenburg (45°), supine, Trendelenburg (45°) positions, each for 15-min duration and 3 readings were taken in each position at 5 min interval. Lastly patient was positioned back to supine position for the surgery to begin. Results: There was a statistically significant decrease of BIS value with a change from supine position to reverse Trendelenburg position (P = 0.02) and increase in BIS value from supine to Trendelenburg position (P = 0.01). Changing of position from supine to reverse Trendelenburg was found to have a statistically significant decrease in MAP (P = 0.005), whereas changing to Trendelenburg position significantly increased MAP compared to supine position (P < 0.001). There was a positive moderate linear correlation between BIS and MAP (r = 0.513, P = 0.004). Conclusion: A change of position from supine to reverse Trendelenburg decreases and from supine to Trendelenburg position transiently increases the BIS values. Abbreviations: BIS - Bispectral Index; SQI - Signal Quality Index; EMG – Electromyography; MAP - Mean Arterial Pressure Key words: Anesthesia; Anesthesia, General; Bispectral Index; Electroencephalography; Electromyography; Monitoring; Positioning Citation: Kamaruzaman K, Izaham A, Rahman RA, Mokhtar MN. Changes in bispectral index (BIS) with different positions during general anesthesia. Anaesth. pain intensive care 2023;27(3):325−331. DOI: 10.35975/apic.v27i3.1922 Received: June 24, 2022; Reviewed: April 10, 2023; Accepted: April 10, 2023