Background: We present a case in which a temporary decrease in train-of-four (TOF) response was observed after reversal of muscle relaxation with a small dose (0.5 mg/kg) of sugammadex administered 42 min after 0.9 mg/kg of rocuronium. At the end of the operation, the TOF ratio was >0.9, and the patient woke normally, without signs of muscle weakness. We describe this temporary decrease in muscle response during muscle relaxation reversal as muscle relaxation rebound and hypothesize that it occurs when the dose of sugammadex is sufficient for complex formation with rocuronium in the central compartment, but insufficient for redistribution of rocuronium from peripheral to central compartments.
Methods: To investigate our hypothesis, we developed and fit a simple pharmacokinetic- pharmacodynamic model of rocuronium, sugammadex, and their interaction to the patient TOF response data.
Results: Simulations using the fitted model indicate that muscle relaxation rebound can occur for doses of sugammadex in a limited critical range.
Conclusions: Sufficiently large doses of sugammadex eliminate the possibility for muscle relaxation rebound, which does not require dissociation of the sugammadex/ rocuronium complex.