Changes in plasma orexin A during propofol-fentanyl anaesthesia in patients undergoing eye surgery

Central orexinergic and noradrenergic neurones are involved in the control of sleep and wakefulness. In addition, previous reports suggest that both neurones may have an important role to play in general anaesthesia. In the present study, we have determined whether general anaesthesia would affect plasma orexin A (OXA) and norepinephrine concentrations. Twenty-two patients undergoing elective ophthalmic surgery under general anaesthesia with propofol, fentanyl, and vecuronium were studied. Arterial blood was collected before and 1 and 2 h after induction of anaesthesia and at emergence to measure plasma OXA, propofol, norepinephrine, and epinephrine concentrations. During anaesthesia, the propofol infusion rate was changed to maintain the bispectral index between 40 and 50. Plasma OXA and norepinephrine did not change during anaesthesia but significantly increased after emergence compared with pre-anaesthesia [from 19.9 (sd 3.2) to 28.3 (4.3) pM, P < 0.01, and from 1351 (146) to 1798 (251) pM, P < 0.05, respectively]. Plasma epinephrine did not change. There was a significant correlation between plasma OXA and norepinephrine (P < 0.05) and also between plasma propofol and OXA (P < 0.05) and norepinephrine (P < 0.01). We found that plasma OXA and norepinephrine significantly increased during emergence from propofol-fentanyl anaesthesia.