Estimating the Plasma Effect-Site Equilibrium Rate Constant (K_e0) of Propofol by Fitting Time of Loss and Recovery of Consciousness

抄録

The present paper proposes a new approach for fitting the plasma effect-site equilibrium rate constant (K_e0) of propofol to satisfy the condition that the effect-site concentration (C_e) is equal at the time of loss of consciousness (LOC) and recovery of consciousness (ROC). Forty patients receiving intravenous anesthesia were divided into 4 groups and injected propofol 1.4, 1.6, 1.8, or 2 mg/kg at 1200 mL/h. Durations from the start of injection to LOC and to ROC were recorded. LOC and ROC were defined as an observer’s assessment of alertness and sedation scale change from 3 to 2 and from 2 to 3, respectively. Software utilizing bisection method iteration algorithms was built. Then, K_e0 satisfying the C_eLOC=C_eROC condition was estimated. The accuracy of the K_e0 estimated by our method was compared with the Diprifusor TCI Pump built-in K_e0 (0.26 min⁻¹), and the Orchestra Workstation built-in K_e0 (1.21 min⁻¹) in another group of 21 patients who were injected propofol 1.4 to 2 mg/kg. Our results show that the population K_e0 of propofol was 0.53±0.18 min⁻¹. The regression equation for adjustment by dose (mg/kg) and age was K_e0=1.42–0.30×dose–0.0074×age. Only K_e0 adjusted by dose and age achieved the level of accuracy required for clinical applications. We conclude that the K_e0 estimated based on clinical signs and the two-point fitting method significantly improved the ability of C_eLOC to predict C_eROC. However, only the K_e0 adjusted by dose and age and not a fixed K_e0 value can meet clinical requirements of accuracy.