The effects of circadian rhythms on the duration of neuromuscular blocking agents are under-investigated. Therefore, the aim of this prospective, observational study was to investigate whether the dosing-time of rocuronium would cause significant differences in the neuromuscular block duration during the four different period of a day in a diurnal based study design. Forty patients were allocated into one of the following four groups according to the surgery timing during a day. Patients undergoing surgery between 07:00 am and 01:00 pm were included in Group M (Group morning, n = 10), between 01:00 pm and 07:00 pm in Group AN (Group afternoon, n = 10), between 07:00 pm and 01:00 am in Group E (Group evening, n = 10), and between 01:00 am and 07:00 am in Group N (Group night, n = 10). All patients received rocuronium in a dose of 0.6 mg/kg. The time to T1 10% and clinical duration were significantly shorter in Group N [24.4 ± 8.0, 28.5 ± 9.0 min, mean ± standard deviation (SD)] when compared with Group AN (32.1 ± 8.6, 36.7 ± 9.1 min, mean ± SD) and Group E (32.5 ± 9.9, 37.0 ± 11.4 min, mean ± SD) (p < 0.05). T1 10% time and clinical duration of rocuronium were significantly shorter when used at nighttime compared to afternoon and evening part of the day. The increased hepatic blood flow and metabolism of rocuronium may be the responsible factors related to this shortening at night.
Key words: Rocuronium, chronobiology, circadian rhythm, neuromuscular non-depolarizing agents, anesthesia, intravenous.
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