Estimation of the effect-site equilibration rate constant using the time-to-peak effect of muscle relaxants measured by train-of-four stimulation during general anesthesia induction

BACKGROUND: The concept of the effect-site concentration of anesthetic agents is important. The effect compartment model can be explained using the concepts of effect-site concentration and effect-site equilibration rate constant (k(e0)). This study confirms that the time-to-peak effect (t(pe)) can be measured easily in clinical practice by applying a priming dose and train-of-four (TOF) during general anesthesia induction, and k(e0) can be calculated from the t(pe) of the four muscle relaxants that are commonly used in general anesthesia. METHODS: Eighty patients who received general anesthesia were divided into the succinylcholine, rocuronium, atracurium, or vecuronium groups. Priming doses of muscle relaxants were administered. The effects of muscle relaxants were quantified by recording the twitch response of the adductor pollicis muscle after stimulating the ulnar nerve. The t(pe) was measured at the lowest TOF value. k(e0) was calculated from the measured t(pe). RESULTS: The k(e0) values of the succinylcholine, rocuronium, atracurium, and vecuronium groups were 0.076 (0.030)/min, 0.228 (0.122)/min, 0.062 (0.011)/min, and 0.077 (0.019)/min, respectively. CONCLUSIONS: It is possible to estimate k(e0) from the t(pe) of muscle relaxants using a priming dose and TOF during general anesthesia induction.