Difference of Plasma Orexin A Levels Between Elderly and Young Patients at Emergence

BACKGROUND:A specific group of neurons in the brain produces hypocretin, also called orexin, a peptide which has been established as an important regulator of anesthesia and emergence in the latest few years. In the animal experiment,we found that the level of orexin A in aged rats was higher when compared with that of the young ones. Whereas the numbers of both the orexin receptor 1 and 2 in aged rats decreased. We wonder if there is a similar phenomenon in human beings which might account for the difference between the intervals of elderly and young patients recovering from anesthesia. This study aims to investigate difference of plasma orexin A levels between elderly patients and young at emergence from sevoflurane-fentanyl anesthesia.

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 1-1.5mg/kg and fentanyl 2-3μg/kg. Following muscle relaxation with iv rocuronium bromide 1mg/kg endotracheal intubation was performed. Anesthesia was maintained with sevoflurane(inhalational concentration: 0.8-1.5 MAC) fentanyl (total 6μg/kg) and target controlled infusion remifentanil (targeted concentration:2-7ng/ml ) along with an oxygen/air mixture (FiO2 = 0.5). Muscle relaxation was maintained with intermittent rocuronium. Inhalational concentration of sevoflurane and injected target concentration were titrated to maintain the bispectral index (BIS) between 45 and 65 during anesthesia. The end-tidal carbon dioxide level was maintained between 30 and 40mmHg by controlled mechanical ventilation. When the surgery was complicated we adjust the concentration sevoflurane to 0.8MAC of the patient and targeted concentration of remifentanil to 2ng/ml and then stop all anesthetics . 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 (1min 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.

EXPECTED RESULTS:The plasma orexin A of group elderly will be higher with the emergence time longer than youth patients.