BACKGROUND: Delayed emergence from general anesthesia frequently occurs in elderly patients, but the reason is not clear. Orexin has been shown to be involved in arousal from general anesthesia. In this study, we examined plasma orexin-A levels in both elderly and young patients during the anesthesia arousal cycle.
METHODS: We recruited 41 patients scheduled for elective lumbar surgery and eventually evaluated 34 patients. Patients were divided into a young group (age 30–55, N = 16) and an elderly group (age 65–77, N = 18). Anesthesia with sevoflurane-remifentanil was titrated to maintain the Bispectral Index between 45 and 65. The times from stopping anesthesia to eyes opening and extubation were recorded. Arterial blood was collected, and plasma orexin-A was determined by radioimmunoassay at the following 4 time points: preanesthesia (T0), 1 hour after anesthesia induction (T1), emergence (5 minutes after tracheal extubation) (T2), and 30 minutes after tracheal extubation (T3).
RESULTS: The times from stopping anesthesia to eyes opening and tracheal extubation were both significantly longer in the elderly group than in the young group (P = 0.004, P = 0.01, respectively). Basal (T0) orexin-A levels were higher in the elderly group than in the young group (T0, 26.13 ± 1.25 vs 17.9 ± 1.30 pg/mL, P < 0.0001). Plasma orexin-A levels did not change during induction of anesthesia in either group but significantly increased at T2 (vs T0, P <0.0001) in both elderly (35.0 ± 1.7 pg/mL) and young (29.2 ± 1.9 pg/mL) groups. Orexin-A levels were significantly higher in the elderly than in the young group at T1, T2, and T3.
CONCLUSION: Plasma orexin-A levels are not responsible for the delayed emergence from general anesthesia in elderly patients.