Plasma orexin A increases at emergence from sevoflurane-fentanyl anesthesia in patients undergoing ophthalmologic surgery.

Central orexinergic and noradrenergic neurons are involved in the control of sleep and wakefulness. In addition, previous reports suggest that both neurons may have an important role to play in general anesthesia. In the present study, we have determined whether general anesthesia would affect plasma orexin A (OXA) and norepinephrine concentrations. Twelve patients scheduled for elective ophthalmic surgery under general anesthesia with sevoflurane, fentanyl and vecuronium were studied. Arterial blood was collected before and 1 and 2h after induction of anesthesia and at emergence to measure plasma OXA, cortisol, norepinephrine and epinephrine concentrations. During anesthesia the inhalational concentration of sevoflurane was changed to maintain the bispectral index between 40 and 50. Plasma OXA, cortisol, norepinephrine and epinephrine did not change during anesthesia but significantly increased after emergence compared to pre-anesthesia (from 14.8+/-1.7 to 21.4+/-1.7 pM, p<0.01, from 26.5+/-5.2 to 52.8+/-6.0 pM, p<0.01, from 263+/-46 to 513+/-89 pM, p<0.01, and from 1239+/-120 to 1631+/-203 pM, p<0.01, respectively). There were significant correlations of plasma OXA with cortisol (r=0.334, p<0.05) and epinephrine (r=0.292, p<0.05) but not with norepinephrine. In conclusion we found that plasma OXA significantly increased at emergence from sevoflurane-fentanyl anesthesia and this was probably via activation of the hypothalamic-pituitary-adrenal axis.