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.

The relationship between bispectral index (BIS) and purposeful intraoperative patient movement is consistent with previous BIS utility studies. 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.