Fifty patients were included in the study, divided into two equal groups (25 in each), underwent spinal fusion surgery.Control group: received normal saline.

Lidocaine group: received lidocaine 2.0 mg/kg slowly IV before induction of anesthesia, followed by lidocaine IV infusion at a rate of 2.5 mg/kg/hr until the end of surgery. We evaluated the end-tidal isoflurane concentration required to maintain AAI index in the range of 20-25 during adult spinal fusion surgery.

This prospective, double-blinded, randomized study was carried out in Assiut University Hospitals, after approval by the local research ethics committee of Assiut Faculty of Medicine, Egypt. Informed consent was taken from each patient.

Patients were randomly allocated into two groups of equal size to receive either 0.9% sodium chloride infusion group 1 (CG), or lidocaine infusion group 2 (LG). Randomization was performed using G1 and G2 registers, which was placed in sealed envelopes prior to study initiation and opened prior to anesthesia by a physician who prepared the intravenous solution and identified it with the patient number, according to the envelope drawn. The solution was handed to another physician, blind to the prepared solutions' content, who was responsible for the anesthesia. The solution volume was equal. The responsible investigator was remained blind to the chosen group until the end of the study. G1 patients (n = 25) were received 10 mL of 0.9% sodium chloride slowly IV just before induction of anesthesia, then infused through 50 mL syringe as lidocaine, and G2 patients (n = 25) were received a loading dose of lidocaine 2 mg ̸ kg (maximally 200 mg) slowly IV just before induction of anesthesia, then the lidocaine infusion started immediately after positioning at a rate of 2.5 mg ̸ kg/h until the end of the procedure (50 mL syringe contained 25 mL 2.0% lidocaine i.e., 500 mg lidocaine plus 25 mL normal saline). Both syringes (10 mL for loading dose and 50 mL for maintenance IV infusion) were labelled by the case number and prepared by another anesthesiologist who did not share in anesthesia.

Anesthesia technique: Patients were monitored with continuous electrocardiography, pulse oximetry and intermittent non-invasive blood pressure measurements every 5 min. Capnography, end-tidal isoflurane concentration (Et-Iso) via AVANCE CS2 Datex-Ohmeda, Inc. USA, and auditory evoked potential monitor (AEP monitor 2 Dia Trade medical engineering) also attached to the patient (one AEP electrode was placed on the center of the forehead, one on the temple, and one behind the left ear over the mastoid bone).

General anesthesia was induced by propofol 2.5 mg ̸ kg and cisatracurium 0.15 mg ̸ kg to facilitate endotracheal intubation. Patients were then assigned to two groups by closed-envelope randomization. In both groups, anesthesia was maintained with isoflurane in oxygen/air mixture at sufficient concentration to maintain AAI index in the range 20-25, and mean blood pressure within 25% of the baseline value. All patients were received 60 mg ketorolac (ketolac) slowly IV after induction of anesthesia, and fentanyl 1.5 µg ̸ kg IV before skin incision and 0.5 µg ̸ kg given IV after 45 min. Reversal of residual muscle relaxant was done using neostigmine and atropine at the end of the operation.

Data collection: Demographic and surgical data include: Age, gender, weight, height, duration and type of surgery, in addition to Et-Iso.

Inclusion Criteria:

• Adult patients underwent spinal fusion surgery ASA I, II and III

Exclusion Criteria:

• History of epilepsy hearing disorders known allergy to lidocaine BMI > 35 significant cardiac diseases significant renal diseases liver dysfunction substance abuse chronic opioid use