Figure 13-20 A computer simulation based on Sheiner and colleagues' model^[224] and data reported by Wierda et al.^[285] The ED₉₅ of rocuronium at the adductor pollicis from this model is 0.33 mg/kg. Rocuronium, 0.45 mg/kg, is given as a bolus at time zero. Muscle X represents a muscle (such as the diaphragm or the laryngeal adductors) that is less sensitive to the effects of nondepolarizing relaxants than the adductor pollicis is but has greater blood flow. In this example, the concentration of rocuronium producing a 50% block (EC₅₀ ) of muscle X is 2.5 times that of the adductor pollicis, but the half-life of transport between plasma and the effect compartment (t_½ k_e0 ) of muscle X is only half as long. The rapid equilibration between concentrations of rocuronium in plasma and muscle X results in a more rapid onset of blockade of muscle X than the adductor pollicis. The greater EC₅₀ at muscle X explains the faster recovery of this muscle from neuromuscular blockade than the adductor pollicis. Lower blood concentrations of rocuronium must be achieved at the adductor pollicis than at muscle X before recovery begins. (Redrawn from Naguib M, Kopman AF: Low dose rocuronium for tracheal intubation. Middle East J Anesthesiol 17:193–204, 2003.)