Altered plasma melatonin concentrations after administration of propofol in continuous infusion

OBJECTIVE: To determine possible variations in plasma levels of melatonin in patients sedated with propofol administered in continuous infusion. PATIENTS AND METHODS: Healthy patients receiving spinal anesthesia for lower limb orthopedic surgery were randomized to 2 groups in this prospective study: group A patients were sedated with intravenous propofol infused at a rate of 3 to 4 mg kg(-1) h(-1) and group B underwent surgery without sedation. Data from these groups were compared with data from 2 other groups. Group C data, from healthy volunteers who did not undergo surgery or sedation, were compared with baseline values. Group D data were theoretical reference values for plasma melatonin levels taken from the literature, for comparisons at baseline and in the range of hypnosis. Hormone levels were determined by enzyme-linked immunosorbent assay at baseline, at 10 and 60 minutes after the start of sedation, and 90 minutes after withdrawal of sedation. RESULTS: Twenty patients were enrolled. No significant between-group differences were detected at baseline (P>.269), 60 minutes after starting sedation or 90 minutes after withdrawing it (P>.347 and P>.057 respectively). Values were significantly different between group B and groups A and D 10 minutes after starting sedation with propofol (P<.001). CONCLUSIONS: Plasma levels of melatonin increased during administration of propofol in continuous perfusion.