Intravenous magnesium re-establishes neuromuscular block after spontaneous recovery from an intubating dose of rocuronium: a randomised controlled trial

Context Intravenous magnesium deepens non-depolarising neuromuscular block. Objective To assess whether intravenous magnesium has the potential to re-establish paralysis in patients who have just recovered from a non-depolarising neuromuscular block. Design Prospective randomised double-blind controlled study. Patients Twenty non-obese patients ranging in age from 18 to 80 years were enrolled. Exclusion criteria were a history of liver, kidney or neuromuscular disease and intake of medications interacting with neuromuscular blocking agents. Intervention After spontaneous recovery from an intubating dose of rocuronium had been achieved (train-of-four ratio >= 0.9), patients were given either a bolus dose of magnesium 50 mg kg(-1) intravenously or an equivalent volume of isotonic saline over 5 min. Main outcome measures The train-of-four ratio was measured every minute until the end of surgery. The primary endpoint was the proportion of patients who experienced a decrease in train-of-four ratio following administration of magnesium or saline. Results Following infusion of the study solution, the train-of-four ratio decreased in all patients in the magnesium group in contrast to none in the saline group (P<0.001). On average, magnesium-induced train-of-four ratio depression reached a nadir of 0.49 after 10 min and lasted for 45 min. Conclusion A bolus dose of intravenous magnesium 50 mg kg(-1) re-establishes a clinically relevant degree of muscle paralysis in patients who have just recovered from a non-depolarising neuromuscular block.