Onset and duration of action of rocuronium - from tracheal intubation, through intense block to complete recovery

Background: The primary objective of this study was to establish the relation between the post tetanic count (PTC) and the time to reappearance of the first response (T-1) in train-of-four (TOF) nerve stimulation following rocuronium 0.6 mg/kg, 0.9 mg/kg, and 1.2 mg/kg. The secondary objective was to evaluate the intubation conditions after 1 min. Methods: One hundred and eight patients were randomised to one of three doses of rocuronium: 0.6, 0.9 or 1.2 mg/kg. Tracheal intubation was performed at 60 s by a blinded investigator During propofol, fentanyl, midazolam anaesthesia the neuromuscular block was monitored by mechanography using TOF stimulation every 12 s. At 6 min intervals, a tetanic stimulation (50 Hz) was applied for 5 s preceded and followed by a 30 s period of 1 Hz stimulation until the reappearance of T-1. Results: There was a significant difference in recovery following the high dose and the two lower doses. The relation between time (min) to reappearance of T-1 (t) and PTC can be expressed as follows: t((0.6 and 0.9 mg/kg)(min)) = 18.8-6.46 root PTC and t((1.2 mg/kg)(min)) = 26.1-9.12 root PCT. T-1 was seen at a mean PTC level of 8 or 9 in all three soups. The intubation conditions were graded as excellent or good in all patients except in two patients following the 0.6 mg/kg dose of rocuronium. Conclusion: The PTC method can be used to predict the time to first response to TOF nerve stimulation during intense rocuronium induced neuromuscular blockade. The relation between PTC and the time to T-1 was prolonged after 1.2 mg/kg compared with 0.6 mg/kg and 0.9 mg/kg. No further improvement in intubation conditions at 60 s was evident by increasing the rocuronium dose from 0.9 mg/kg to 1.2 mg/kg.