TITLE: THE BISPECTRAL INDEX PREDICTS PATIENT RESPONSE TO VERBAL COMMAND DURING THE INTRA-OPERATIVE WAKE-UP TEST AND SCOLIOSIS SURGERY

AUTHORS: Peter C. Laussen, MBBS, Mary E. McCann, MD, Julianne Bascik, MD, Lorna J. Sullivan, RN, Susan Auble, RN, Robert Brustowicz, MD
AFFILIATION: Children's Hospital, Boston, MA.

INTRODUCTION: Spinal cord injury is a potential complication during scoliosis surgery. At our institution, an intra- operative wake-up test is routinely performed after straightening of the vertebrae to confirm preserved motor function of the lower limbs. The bi-spectral index (BIS) has been recommended as a monitor of the depth of anesthesia, and correlated to involuntary patient movement at the time of a surgical stimulus¹. This study evaluated BIS as a predictor of voluntary patient movement to verbal stimulus during the intra-operative wake-up for scoliosis surgery.
METHODS: Following IRB approval and informed consent, 36 wake-up tests were performed in 32 patients undergoing idiopathic scoliosis correction. BIS, mean arterial pressure (MAP) and heart rate (HR) were compared at 3 time points, T1) prior to starting the wake-up, T2) time of patient movement to command, and T3) after the patient was re-anesthetized. The anesthesiologists were blinded to the BIS. The anesthesia technique was not controlled; 15/32 patients were maintained with a fentanyl infusion and N₂0, while 17/32 patients received intermittent fentanyl boluses, N₂0 and low dose isoflurane. At the time of wake-up the patients were told a specific color (teal) to remember and on the second postoperative day were interviewed for explicit recall. Data was analyzed using t-Test and expressed as mean (SD) with significance p<0.05.
RESULTS: Mean age was 14.3 (2.8) years and weight 57.7 (21.3) kg. Changes in MAP, HR and BIS at the 3 time points are shown in the table. In all cases there was a significant increase in BIS predicting a positive wake-up response. No patient recalled intra-operative pain, 1 patient recalled the wake-up test but not the color, and 4 patients recalled the color teal. All patients recovered uneventfully.

P<0.001 time 2 vs. times 1 and 3; # P<0.001 time 3 vs. time 1; P<0.01 time 2 vs. time 1.

DISCUSSION: The increase in BIS correlated with patient movement on verbal command as the endpoint during the wake- up test, with a 15.6% incidence for explicit recall of intra- operative events. BIS is a useful clinical monitor for predicting depth of anesthesia and patient movement during the wake-up test for scoliosis surgery.
REFERENCES:

1. Anesthesia Analgesia 1997;84:891-99.