Neuromuscular block by vecuronium: simulation with a flow-volume model

The time profile of the neuromuscular block produced by a single bolus administration of vecuronium was simulated by a new model for the access of the relaxant to the receptors on the motor end plates. The receptors were assumed to be kinetically a part of the interstitial space of the muscle. The time course of the neuromuscular block was defined by the time course of the vecuronium concentration in the interstitial space. The concentration there was derived from the plasma flow to muscle, the volume of the interstitial space in muscle, and the time profile of vecuronium concentrations in plasma. The model describes well the time lag needed to reach the peak submaximal block, its magnitude, as well as the time course of recovery from the maximal block. The limits of the model, evident in less than optimal simulation of the neuromuscular block by two doses of vecuronium in rapid succession, were attributed to the inadequate description of the vecuronium concentrations in plasma immediately after the bolus injection.