• Susumu Kawanishi, Kazunori Hamanami, Toru Takahashi, and Masaki Matsumi.
• Emergency and Critical Care Center Tsuyama Central Hospital, Tsuyama 708-0841.
• Masui. 2012 Aug 1;61(8):820-5.

BackgroundAlthough the bispectral index (BIS) has been established as a common index of anesthetic depth, there is a possibility that head-up position may influence BIS values under general anesthesia. This study examined whether beach chair position with 57 degrees head-up would cause the variation of BIS values during shoulder surgery.MethodsTwo groups of patients were scheduled for surgery, one was supine position group, and the other was beach chair position group. Anesthesia was induced with propofol and rocuronium, and maintained with sevoflurane (end-tidal concentration 1.0-1.2%). The BIS values were recorded manually until 120 minutes after the onset of positioning and evaluated at each 30 min interval.ResultsThere was no time-dependent difference in BIS values during supine position. In contrast, BIS values in beach chair position group showed a marked downward-trend through the measurement period. End-tidal anesthetic gas concentration and mean blood pressure did not significantly differ between the groups consistently.ConclusionsTo our knowledge, this is the first report of the effect of beach chair position on BIS values intraoperatively. This result indicates that the beach chair position causes a time-dependent decrease in BIS under general anesthesia.

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