DESIGNING: Forty patients with ASA physical status I or II scheduled for elective lumbar surgery under general anesthesia (lasting for 2h to 4h) were enrolled. Anesthesia was induced with propofol 1-2mg/kg and sufentanyl 0.2-0.3μg/kg. Following muscle relaxation with iv cisatracurium besylate 0.2mg/kg endotracheal intubation was performed. Anesthesia was maintained with sevoflurane (inhalational concentration: 0.8-2.0 MAC) and target controlled infusion remifentanil (targeted concentration:2-6ng/ml ) along with an oxygen/air mixture (FiO2 =0.5). Muscle relaxation was maintained with intermittent. Inhalational concentration of sevoflurane and injected target concentration were titrated to maintain the bispectral index (BIS) between 40 and 60 during anesthesia. The end-tidal carbon dioxide level was maintained between 30 and 40 mmHg by controlled mechanical ventilation. When the surgery was completed the investigators adjust the concentration sevoflurane to 0.8MAC of the patient and targeted concentration of remifentanil to 2ng/ml then stop all anesthetics and adjust the oxygen flow to 6.0 L/min, at the same time the doxapram group iv doxapram 1mg/kg, the controlled group given equal volume of saline. Record time from stopping anesthetics to emergence. Arterial blood (2ml) was collected at the following time,such as before and 1h after induction of anesthesia, at emergence (1 min after tracheal extubation) and half an hour after tracheal extubation. This was centrifuged at 3000 rpm for 15min at −4 ◦C in order to separate plasma then stored at −80 ◦C until assay for orexin A concentrations.