Effect of beach chair position on bispectral index values during arthroscopic shoulder surgery

Bispectral index (BIS) monitoring reduces the cases of intraoperative awareness. Several factors can alter BIS readings without affecting the depth of anesthesia. We conducted a study to assess the impact of beach chair position (sitting position) on BIS readings. General anesthesia was administered to 30 patients undergoing arthroscopic shoulder surgery. Patients were kept in neutral position (supine) for 10 minutes and BIS readings, mean arterial blood pressure, heart rate, end-tidal carbon dioxide, and end-tidal sevoflurane were recorded. Patients were then shifted to beach chair position. After 15 minutes, data were recorded. A significant decrease in BIS values (P < 0.01) associated with a position change from neutral position to beach chair position was evident. BIS values are significantly decreased in the beach chair position compared with the neutral position and might affect interpretation of the depth of anesthesia.