Intravenous anesthetic agents as far as inhaled agents produce a dose depended increase in latency and decrease in amplitude of SomatoSensory Evoked Potential (SSEP). Dexmetedomidine, a highly selective a2 adrenergic agonist, not only minimizes the anesthetic agents but also the opioids, reducing the analgesic demands. The effect of dexmedetomidine on SSEP has not been elucidated. We aimed to investigate alterations on somatosensory SSEP in adults during posterior spinal fusion surgery before and after Dexmedetomidine administration.

Patients 18-75 years old, ASA (physical status classification system) I-III, scheduled for elective posterior spinal fusion surgery were enrolled in this prospective study. After induction in anesthesia, it was applied SSEP monitoring and a baseline test was performed after 15min (in order to wash out the propofol used for induction). Infusion of Dexmedetomidine was started at a bolus dose of 1mcg/Kg following by 0.7mcg/Kg. Bispectral Index (BIS) monitored the depth of anesthesia and an adequate level (40-50) of anesthesia was maintained by sevoflurane. SSEP were recorded intraoperatively from the tibial nerve (P37) and data were analyzed over that period.

Inclusion Criteria:

• Patients with ASA physical status 1-3

Exclusion Criteria:

• Patients with ASA physical status >3,
• Body Mass Index (BMI) over 30,
• indication for rapid sequence induction,
• any contraindication for receiving b-blocker,
• Glasgow Coma Scale (GCS) <13,
• history of drug abuse,
• neurologic deficit or preoperatively foreseen delayed extubation,
• preoperative heart rate<45.