Effects of intravenous lidocaine on somatosensory and motor evoked potentials during spine surgery

INTERVENTION: Each study patient alternately receives two anesthetic treatments. The order of administration is determined randomly. The treatments are propofol at 50 mcg/kg/h, or propofol 25 mcg/kg/min + lidocaine 1 mg/kg/h. During both treatments, maintenance anesthesia also includes fentanyl 1mcg/kg/h, ketamine 2 mcg/kg/min and diazepam 10mg. Patients additionally receive isoflurane, typically 0.5%, adjusted as needed by the attending anesthesiologist to maintain steady hemodynamics. The total duration of each treatment is 120 minutes, and each treatment is administered for 30 minutes prior to logging IONM data for this study. Prior to the institution of the lidocaine infusion, each patient receives a loading dose at 1mg/kg over 10 minutes. Primary outcome measurements (SSEP amplitude and MEP threshold voltages) are made by a neurophysiological technologist who is blind to the treatment being administered. CONDITION: Multilevel posterior spinal fusion ; Musculoskeletal Diseases ; Multilevel posterior spinal fusion PRIMARY OUTCOME: 1. Somatosensory evoked potential amplitude is measured using a Cadwell Elite intraoperative monitoring system, at 3‐5 minute intervals; 2. Motor evoked potentials threshold voltage is measured using a Cadwell Elite intraoperative monitoring system, at 10‐20 minute intervals SECONDARY OUTCOME: 1. Isoflurane concentration is measured using a General Electric Datex Ohmeda operating room patient monitor at 5 minute intervals; 2. Heart rate is measured using a General Electric Datex Ohmeda operating room patient monitor at 5 minute intervals; 3. Blood pressure is measured using a General Electric Datex Ohmeda operating room patient monitor at 5 minute intervals; 4. Temperature is measured using a General Electric Datex Ohmeda operating room patient monitor at 5 minute intervals; 5. Estimated blood loss is measured at the conclusion of the procedure based on cell salvage system data, irrigation and intraoperative blood administration INCLUSION CRITERIA: 1. Patients undergoing multi‐level posterior spine fusions requiring both somatosensory and motor evoked potential monitoring 2. Ages within the age range of 18 – 70 years.