The bispectral index and explicit recall during the intraoperative wake-up test for scoliosis surgery

In this prospective study, we evaluated the bispectral index (BIS) and postoperative recall during the intraoperative wake-up examination in 34 children and adolescents undergoing scoliosis surgery. Each anesthesiologist was blinded to BIS values throughout surgery and the wake-up test. The BIS, mean arterial blood pressure, and heart rate were compared at: before starting the wake-up test, patient movement to command, and after the patient was reanesthetized. The anesthetic technique for Group 1 was small-dose isoflurane, nitrous oxide, fentanyl, and midazolam and for Group 2 was nitrous oxide, fentanyl, and midazolam. Controlled hypotension was used for all cases. At patient movement to command the patients were told a specific color to remember (teal) and on the second postoperative day were interviewed for explicit recall of the color and other intraoperative events. A total of 37 wake-up tests were performed in 34 patients. There was a significant increase in both groups of BIS (P < 0.001), mean arterial blood pressure (P < 0.001), and heart rate (P < 0.01) at the time of purposeful patient movement followed by a significant decline in BIS after reintroduction of anesthesia (P < 0.01). No patient recalled intraoperative pain, one patient recalled the wake-up test but not the color, and five patients recalled the specified color. We conclude that BIS may be a useful clinical monitor for predicting patient movement to command during the intraoperative wake-up test, particularly when controlled hypotension is used and hemodynamic responses to emergence of anesthesia are blunted.