Background: Operations are typically associated with sleep and other circadian rhythm disturbances. The present study was set up to evaluate the influence of spinal and general anaesthesia associated with knee surgery on the circadian rhythm of melatonin, which has sleep inducing properties. Previously this context has been studied only in some invasive operations and it might be that general anaesthesia induces more disturbances on circadian rhythm of melatonin than operations done with patients awake.
Methods: The circadian secretion pattern of melatonin was monitored during the pre- and postoperative evenings, nights and mornings to clarify possible anaesthesia/surgery-induced changes in the nocturnal secretion of melatonin and in the phase of the melatonin rhythm. The study included 20 patients scheduled for minor orthopaedic operations. The patients were randomised to receive either spinal or general anaesthesia. Melatonin was measured from evening and morning saliva samples radioimmunologically. The nocturnal urine before and after surgery was radioimmunologically examined for 6-hydroxymelatonin sulphate.
Results: Melatonin secretion evaluated from the saliva samples was significantly diminished during the first postoperative evening as compared with that during the preoperative evening (P<0.001). There was also a significant decline of 26% (P<0.05) in postoperative 6-hydroxymelatonin sulphate excretion. There was no significant difference in melatonin secretion between the spinal and general anaesthesia groups.
Conclusion: Our findings suggest that anaesthesia in conjunction with surgery acutely disturbed the normal circadian rhythm of melatonin by delaying the onset of nocturnal melatonin secretion.